Learning Objectives
From reading and studying this chapter, you should be able to:
- Describe insect structure and body parts
- Explain the various stages of growth and development of insects
- Discuss the four basic insect pest management tactics
- List and explain the 8 different ways that insects attack and damage plants
- Give specific examples of insects in each of the above damage categories
- Identify commonly encountered pest insects and the damage they cause
- Be familiar with terminology related to insects and entomology
Introductory comments
In this chapter you will learn the critical characteristics of insects and mites that can help you detect and identify a pest problem and decide on the appropriate management solution. After reviewing the general biology of insects and some general concepts of pest control, we review the common pest symptoms you encounter along with insects and mites that are their likely cause. This chapter is designed to provide you with information you will need to prepare for the Insect Management portion of the IAH certification test. Terms in bold type are explained in the Glossary of Terminology at the end of the chapter. You should know these for the examination. This chapter provides pictures of individual insects and the damage they cause. We suggest that you utilize the pictures as you go through the chapter. The IAH examination will require you to know both written material and the content from the pictures. For further preparation we also advise that you familiarize yourself with the PurduePlantDoctor.com web site so that you can take advantage of the hundreds of photos and descriptions to help you study.
WHAT ARE INSECTS AND MITES?
Insects and mites belong to group of animals called arthropods because their bodies share some common structures. The name arthropod, which means “jointed foot” was given to this group because the legs of all its species are jointed. Unlike people, who support their limbs with an internal skeleton, arthropods have an exterior support structure called and exoskeleton that also serves as their skin. Arthropods are direct descendants of earthworm-like ancestors and include the vast majority of species in the animal kingdom. These include lobsters, shrimp, crabs, pillbugs, millipedes, centipedes, scorpions, spiders, mites, and insects.
Insect Structure
Insects are segmented and have three basic body regions; head, thorax and abdomen (fig. 1). The head bears the eyes, antennae (feelers), and mouthparts and contains the brain.
Fig 1. Insect body
The thorax is directly behind the head. It has three segments that are usually firmly joined together, and each of these segments usually has one pair of jointed walking legs.
The wings, if present, are on the second and third thoracic segments. The pronotum is a distinctive piece of exoskeleton that lies between the head and the attachment of first pair of wings on the first segment of the thorax. In some insect groups, like grasshoppers, it can be greatly enlarged to cover wing attachments on the second and third thoracic segments.
The abdomen is usually as long or longer than, the head and thorax combined. It has a variable number of distinct segments that contain the gut and reproductive organs. Externally, it is usually softer than the head and thorax because it needs to be flexible enough to hold food, water, air, fat reserves and eggs.
Fig 2. Insect heads
The head of adult insects has various types of mouthparts (fig. 2). Beetles, bees, ants, grasshoppers, lacewings and dragonflies have chewing mouthparts. Insects with piercing and sucking mouthparts have a sharp, hollow beak-like structure used to penetrate plant or animal tissue and suck up fluid. Examples are aphids, scale insects, leafhoppers, plant bugs, mosquitoes, and all of the predatory true bugs. Lapping and sponging mouthparts are primarily found in certain flies, including the house flies. The siphoning mouths of butterflies and moths are coiled into a long tube that is used to suck liquids, such as nectar from flowers. Some adult insects, such as mayflies, or adult male scale insects, have nonfunctional mouthparts. Like adults, the mouthparts of immature insects can be shaped to chew or to suck fluids.
Insects have three pairs of true legs, one on each segment of the thorax. These legs are jointed and are shaped to serve specific functions. For example, the hind legs of grasshoppers are long and springy to help them jump. The front legs of Japanese beetles are modified for digging in the soil. The larval stages of some insects, (e.g. caterpillars and sawflies) can also walk with the fleshy, unjointed legs called prolegs. These appendages are not jointed and are attached to segments of the abdomen.
Most species of insects have two pairs of wings as adults. These wings can be clear, opaque, or covered with fine scales as in the case of moths and butterflies. Some insect groups such as grasshoppers and beetles, have a thickened front pair of wings. These protect the abdomen and wings when the insect is not flying. Flies have only one pair of fully developed wings. The hind pair of wings is greatly reduced. In yet other groups of insects the number of wings present can be quite variable.
Insect Growth and Development
Most insects start life in an egg stage. The process of egg laying is called oviposition. Adult females of many species lay their eggs in the area where their young feed. For example, hawthorn lacebugs lay eggs on the leaves where young nymphs feed. Lesser peach tree borer moths, lay eggs on the bark of flowering cherry where caterpillars can bore into the trunk. Insects use specialized organs called ovipositors to place their egg in the correct location (figs 3- 4). Some ovipositors are located internally except when extended from the abdomen during oviposition, (as with most flies); others are external and obvious (as with crickets, cicadas and sawflies). A few insects, such as aphids, give birth to live young.
The two ways that insects grow from an egg to adult are called simple and complete metamorphosis. Simple metamorphosis occurs with those insects in which the young look very similar to the adults, except that wings are not present and they are not reproductively mature. In the immature stage, these insects are called nymphs. Insects with simple metamorphosis that attack woody plants include aphids, cicadas, plant bugs, leaf hoppers, plant hoppers, tree hoppers, mealybugs, scales, thrips, crickets, and katydids.
Fig 5. Caterpillar vs. Sawfly
Insects with complete metamorphosis have a worm- like, maggot-like, or grub-like immature stage called the larva. At one extreme, the body plan of larval insects can be clearly recognizable as in the case of caterpillars, and sawflies (fig. 5). There, jointed walking legs are clearly visible on the thorax and fleshy unjointed walking appendages, called prolegs, are easily distinguished on the abdomen. At the other extreme, the body plan of larval insects is hard to distinguish, as in the case of fly maggots which change into an intermediate form called pupae before they become winged adults. Pupae are inactive and do not feed. They are usually found in a protected location, such as within a cocoon, under tree bark, or within the soil. Insects with complete metamorphosis include all beetles, butterflies, moths, bees, wasps, ants, flies, and lacewings. Important woody plant insect pests with complete metamorphosis include spongy moth, fall webworms, Japanese beetles, and European pine sawflies.
As both nymphs and larvae grow, they must shed their skins (or exoskeletons) through a process called molting. Most species of insects molt a set number of times before they become adults. The distinct immature stages between successive molts are called instars. The first instar is the form of the insect that hatches from the egg. The second instar is the form the insect takes after the first instar molts, and so on. For example, Japanese beetle grubs have five instars. Male spongy moth caterpillars have five instars and females six. Many insects are susceptible to management activities at certain instars. For example, applications of certain insecticides, like Bacillus thuringiensis, are most effective against early instars of pests. Some parasitic wasps attack early instars, and others later instars.
Adult insects are characterized by having wings and by being reproductively mature. (With insects, it seems that there are exceptions to every rule; many adult aphids and all adult fleas are wingless.) Once an insect reaches an adult stage, it never grows any further, and never molts again. Therefore, small beetles do not grow into large beetles, and small flies do not grow into large flies.
The rate of insect growth and development largely depends on temperature and the genetic traits of the species. Within limits, warmer temperatures speed development and shorten generation time. Time required for an insect to complete one generation varies considerably with the type of insect, the availability of food, and to some degree the geographical location and climate. Tuliptree aphids can complete a generation in about 10 days under ideal conditions and they have many generations a year on tuliptree (Liriodendron tulipifera). In comparison, the eastern tent caterpillar has only one generation per year. Euonymus scales have only two generations per year in northern Indiana and three generations per year in Louisiana! In summer, numbers of spider mites on honeylocust or burning bush increase more rapidly in a warmer southern exposure than in sites with a cooler northern exposure.
In climates with cold winters, insects either die or go into an overwintering protective state of arrested development called diapause. A given insect species diapauses in a specific state of development. For example, spongy moth caterpillars spend the winter as eggs, Zimmerman pine moths as larvae, and lacebugs as adults.
Importance of growth and development to pest management
For the most part, immatures and adults with simple metamorphosis feed and injure the same parts of a woody plant. These pests should be monitored by examining susceptible parts of the plant for both the pests and their natural enemies. Likewise, applications of insecticides can be effective against adults and larvae feeding on these plant parts. For example, both adult and immature lacebugs feed on leaves where they can be killed by topical insecticide applications.
Larvae and adults of most species with complete metamorphosis will often use different foods. In many cases only the larvae injure the plant when they feed. For example, adult moths, flies, and wasps of most woody plant pests feed on nectar and pollen, while their immature stages feed on plants. Applications of pesticides usually will only kill immature stages, not adults or pupae. These pests should be monitored by examining their feeding sites for eggs and early signs of damage by the immature stages. Specialized traps have been developed for some species of insects to monitor the flight of adults to help time management activities that target damaging immature stages. Pheromone traps, are baited with the scent of a female to track males that are attracted to the scent. These are commonly use to monitor traps of clearwing moth borers.
As a group, beetles are a notable exception with adults and immatures injuring plants. Still, pupae do not feed. In some cases as with the elm flea weevil, the adults and the larvae feed on leaves. In other cases like the Japanese beetles adults consume leaves, flowers and fruit and the immature grub stage feeds. on roots. Monitoring and management activities need to be directed to the susceptible part of the plant at the proper time of year.
Mites
Mites are not insects but are classified with the insects and several other groups in the phylum Arthropoda. Mites are in the class Arachnida, which also includes spiders and scorpions and the order Acari. Mites have two body regions and usually four pairs of legs. They lack wings.
Mites that are important to woody plants measure about 1/50″ or smaller in size (fig. 6) when fully grown. Spider mites are important pests of spruce, honeylocust, oaks, maples and crabapples. They discolor leaves by extracting leaf fluids. Other mites, in a group of closely related families are called the eriophyid mites. They are characterized by a cigar shaped body and 4 visible legs (fig.7). Some species, like the hemlock rust mite discolor leaves in the same way as spider mites. Other species cause the plant to produce galls, like the ash flower gall that will be discussed later (fig.30).
Not all mites are harmful to woody plants. Small, fast-moving, translucent, tear drop shaped mites in the family Phytoseiidae regularly feed on spider mites in the landscape.
HOW INSECTS AND MITES INJURE WOODY PLANTS
Most insects and mites injure woody plants when they feed on them. Insects can have either chewing or sucking mouth parts. Insects with chewing mouth parts injure plants by cutting into or removing whole parts of plant tissue. Examples include defoliation by eastern tent caterpillar (fig. 38), skeletonization of leaves by Japanese beetles (fig.49), boring into a tree trunk by a bronze birch borer (figs. 69- 70), and boring into a leaf by a birch leaf miner. Insects with sucking mouth parts injure plants when they pierce plant tissue and suck out its contents. Examples include the white spots on the surface of a cotoneaster, azalea or serviceberry where lacebugs have extracted the green contents of leaf cells (fig.11). Alternatively, insects such as the honeylocust plant bug can distort leaves by killing parts of the leaf as it unfolds from the leaf bud (fig.9). Similarly, leaves and stems may be curled when insects such as aphids pierce plant stems and suck fluids from developing leaves and shoots. In many cases, however, the damage is caused by the accumulation of honeydew and unsightly black sooty mold (fig.14).
Insects can also injure plants when they lay eggs or oviposit into plant tissue. For example when a cicada lays an egg into the stem of an oak tree it can kill the shoot that lies beyond the egg laying site. Gall making is another form of injury that occurs when plant tissue swells around the site where an insect is feeding. An example of this is when the horned oak gall maker lays an egg in the twig of a pin oak and a gall forms around the developing larvae (fig.31).
PEST MANAGEMENT TACTICS
When should you act to protect a plant from insect and mite injury?
When insects and mites feed on plants they injure them. When this injury harms plant health, or makes a client dissatisfied with plant appearance, the plant is damaged. This concept is critical to the successful management of client properties. Detection of a single insect does not, by itself justify treatment because it is not likely to cause enough injury to damage the tree. For example, consider a 40′ tall oak tree with approximately 100,000 leaves. Loss of 10 leaves to a single caterpillar is not likely to harm plant health. More importantly, your clients are not likely to notice it. Most people require about 10%, or 10,000 leaves to be missing for its appearance to be unacceptable. At this level, plant health is not likely to be affected. Other factors, such as whether the caterpillars are dropping their excrement on your client’s picnic table should also be part of the assessment process
Pest management tactics fall into four basic categories, cultural, mechanical, biological, and chemical control. The following is a review of each of these categories.
What tools can you use to protect plants from damage?
Cultural control
- Inspect plants for pests before they are lined out in the field or planted in the landscape. New plant material arriving into the nursery or landscape stock yard can be an important source of future problems.
- Place plants in their appropriate landscape environment. Consider light, drainage, and fertilization requirements.
- Plants should be planted to the proper depth to prevent injury that could make plants more attractive to pests.
- Do not over or under fertilize your plants.
- Mulch plants in landscapes to an appropriate depth (2-4″) to conserve soil moisture and to protect roots from extreme temperatures. Do not put mulch against the tree trunk above the root collar. Mulching helps prevent bark injury from lawn mowers or string trimmers by reducing the need to mow around tree trunks.
- Prune plants appropriately to promote good plant structure. Do not prune at a time that attracts pests to trees. In Indiana, this means that you should not prune birches in June and July, since this will attract bronze birch borers to the plant. Do not prune oaks during the growing season to avoid attracting the sap beetles that transmit a disease called oak wilt.
- Use plants resistant to pests when they are available. Many plant varieties are resistant to insect pests. For example “Prairie Fire” is a crabapple that is resistant to Japanese beetles and apple scab.
- Use a wide variety of plants in your landscape design. Increasing plant diversity will make it more difficult for pests to spread between plants. Further, adding flowers to the landscape can feed and attract insects who attack and help control insect pests.
Mechanical control
Physically remove and destroy pests to eliminate pest problems. Evergreen bagworms are a good example. This insect starts its life in a small group of eggs that spends the winter in the leaf covered body of their mother on a tree (fig.40). When you remove the bags prior to when eggs hatch in late May or early June, you can eliminate the source of damaging caterpillars.
Prune out limbs infested with a pest to avoid further damage. Oystershell scale (fig.17) can often be controlled on a dogwood in this manner. As an armored scale, this insect spends most of its life beneath a waxy cover on a twig. Infestations can only spread when the eggs hatch and the young scales crawl to find a new place to settle to feed. Simply pruning out infested shoots after scales have settled and can no longer walk removes scales that can spread to other parts of the plant.
Biological control
Not all insects, mites, and diseases in a nursery or landscape are harmful to plants. Many of these are predators, parasites or pathogens that feed on the pests themselves. Predators attack, kill and eat multiple numbers of pests. Parasites lay an egg in or on a pest. After the egg hatches it consumes the pest, usually killing it as develops into an adult. Pathogens are free living microscopic organisms (bacteria, fungi, viruses, etc.) that invade a pest’s body and cause a disease that weakens or kills it. Some natural enemies are generalists and feed on many pest species. Others are specialists and feed on one or a few species. Biological control is the use of living organisms to reduce or prevent crop damage. There are three approaches to using these natural enemies to control pests; classical biological control, conservation, and augmentation.
Conservation is the adoption of practices that nurture native natural enemies that are already present in landscapes and nurseries. Practically speaking this means learning to distinguish between pests and natural enemies, avoiding the use of long-lasting broad-spectrum insecticides, and providing alternate food in the form of pollen and nectar as flowering plants. To get the most out of these flowering plants it is best to minimize applications of pesticides (see section on protecting pollinators).
Chemical control
Pesticides can be applied to plants by spraying leaves, drenching the soil, or by tree injection. Materials that are sprayed on to leaves can kill surface feeding insects on contact, or by forcing them to eat poisoned food. Many insects, however, are concealed within plant webs, or beneath leaf or trunk surfaces. Some foliar pesticides are systemic and can move through leaf and bud tissues allowing them to kill insects like leaf miners and aphids that are not completely exposed to the leaf surface. Other insecticides applied as soil drenches or as direct injections into the plant can move through the vascular system, killing borers, leaf miners, sucking and chewing insects.
According to the US Environmental Protection Agency, there are three kinds of pesticides, conventional, reduced risk and biopesticides. Conventional pesticides are typically synthetic materials that can kill many types of insects. Reduced Risk pesticides are those that meet the US EPA’s standard for posing less risk to the environment and humans. These tend to be less toxic and more selective in the insects that they kill. Biopesticides are a group of pesticides derived from natural materials, including animals, plants, and bacteria.
Conventional Pesticides
Conventional pesticides have a wide range of toxicity and residual activity against pests. Most control the target organism by disrupting its nervous system and can be categorized into groups by chemical structure. The following groups have seen numerous applications in the landscape industry.
- Organochlorines are very stable compounds and may persist in the environment for long periods. Examples include methoxyclor, and kelthane, two materials no longer labeled for landscape use.
- Organophosphates have replaced many of the uses of the organochlorines. Most organophosphates deteriorate rather rapidly in the environment. They do not tend to bioaccumulate. Examples include acephate, dimethoate, diazinon, and chlorpyrifos. Both diazinon and chlopyrifos are no longer registered for use in the urban landscape with the exception of some turf uses. Dicrotophos or Bidrin is labeled only for injection into trees.
- Carbamates resemble organophosphates in many ways. However, they tend to have even lower toxicity to mammals. Examples include carbaryl. Although fenoxacarb and indoxacarb are in this family, they act and are listed as insect growth regulators.
- Neonicotinoids (also called Chloronicotinyls) form a relatively new class of compounds with very low mammalian toxicity and long-lasting systemic activity in plants. Examples include acetamiprid, clothianidin, dinotefuran, imidacloprid and thiamethoxam.
- Pyrethroids are synthetic materials that imitate the activity of a naturally occurring botanical compound. They are relatively nontoxic to mammals and find a tremendous variety of uses in insect pest control. Examples include bifenthrin, cyfluthrin, deltamethrin, fluvalinate, lamda-cyahlothrin, and permethrin.
Reduced Risk Pesticides
This group includes chemical compounds and liquid formulations of biological organisms that kill pests that are considered to be reduced risk compounds due to their toxicological profile. These materials tend to be compatible with some natural enemies in the landscape because they are active for shorter periods of time and because they are specifically active against the target pest. The following types of materials are available:
- Insect growth regulators (IGRs) usually are synthetic chemicals that look and act like insect hormones. They either kill insects during the moulting process or make adults sterile. Generally, these materials are most active against immature insects that must still undergo several molts. They have little or no effect on the pupal stage of natural enemies growing inside host pests. Examples include, azadirachtin, cyromazine, diflubenzuron, fenoxycarb, indoxacarb, halofenozide, pyriproxifen, and tebufenozide.
- Horticultural oils are petroleum- or plant-based hydrocarbon chains with insecticidal activity. Toxicity to insects is due to suffocation or membrane disruption. Some formulations of horticultural oils are labeled for dormant applications. Dormant oil applications are made to plants in winter dormancy, and summer oil applications are made on actively growing plants during the summer.
- Insecticidal soaps are potassium or sodium salts of fatty acid chains. They tend to be very good at controlling soft bodied insects by smothering them or disrupting cell membranes.
- Ryanidine inhibitors are a novel class of compounds that attack insect muscle receptors. These tend not to cause outbreaks of spider mites, but are long lasting in their ability to kill pests. Examples include chlorantraniliprole and cyantraniliprole.
- Lipid biosynthesis inhibitors. These products interfere with the capacity of insects to digest fats. These systemic insecticides can be applied to the foliage to kill sucking insects including whiteflies, aphids, scales, mealybugs, thrips and mites. They are relatively selective with minimal impact on beneficial insects. Examples include spirotetramat and spiromesifin
- Microbial derived insecticide. These compounds, also known as macrocyclic lactones, have relatively low toxicities to humans. They vary in selectivity and tend to be systemic with abamectin being especially effective against mites and whiteflies and sawflies, spinosad being the standby for caterpillars and sawflies, and emamectin benzoate, being a long lasting product for beetle, sawfly, and caterpillar defoliators, as well as borers, including emerald ash borer.
Biopesticides
Insecticides most commonly encountered by the nursery industry include pesticides derived from plants, animals, bacteria, and minerals. Use of most other insecticides in this group, like genetically modified plants, and sex pheromones are not widely used in the industry. Like reduced risk pesticides, these organisms are less toxic and require understanding of pest biology for their effective use.
- Botanicals are plant extracts that have insecticidal properties. Examples include azadirachtin, pyrethrin, rotenone, neem oil, citrus oil, garlic oil, hot pepper wax and cinnacure. Note that while azadirachtin and neem oil come from the neem tree, azadirachtin works as an insect growth regulator and repellant, whereas neem oil may or may not contain azadirachtin and may only act to smother insects.
- Microbial pesticides. These insecticides are formulations of microorganisms that kill insects. Bacillus thuringiensis (BT) is the most effective and widespread example. Specific strains, like israeliensis, kurstaki, tenebrionis, target gnat-like flies, caterpillars and beetles respectively. Milky spore (Bacillus popilliea), however is an infamous example of commercially available microbial that does NOT control white grubs.
- Nematodes are formulations of living organisms that can be applied with conventional spray equipment. Examples include entomophagous nematodes. These animals swim into or near the insect when applied to the plant or soil and kill their target host. They must have adequate moisture and warm enough temperatures to kill their target pests. They can be quite effective for controlling black vine weevil grubs in container plants.
The following guidelines will increase the effectiveness of all chemical controls and decrease the possibility of insecticide resistance in the landscape:
- Spray only when pests are causing a problem.
- Restrict sprays to infested plants.
- Time pesticide applications to coincide with susceptible stages on insect pests.
- When applying conventional pesticides, change classes (eg. organophosphate to pyrethroid) at the beginning of every new pest generation.
Integrated Pest Management (IPM)
Integrated pest management is a systematic approach that helps you make decisions that manage the problem with a minimal impact on the environment. For example, once you have learned to distinguish between pests and natural enemies, it is possible to evaluate their potential for damage or control by regularly monitoring their progress as you inspect the landscape for pests. By inspecting a site on a regular basis you can delay applying controls until pests actually threaten plant appearance and give natural enemies more time to establish themselves so they can work to prevent plant damage. When possible, choose alternative pesticides that specifically target pests, or have short residual activities to conserve natural enemies that are already protecting plants in the landscape.
POLLINATOR SAFETY
Honeybees, bumble bees and their wild relatives provide vital services to the environment and are critical to safeguard our food supply. Any insecticide that can kill a wasp, will kill a bee. This includes a wide majority of the insecticides on the market today. A careful read of any insecticide label will include a warning that prohibits product use where bees are actively foraging. For most insecticides, this means flowers should not be sprayed with insecticides during the day when bees are actively foraging. But to be really safe, it is important NOT to apply foliar pesticides to any plant that is flowering, since residues can also be toxic. Soil applications of neonicotinoid pesticides can be long lasting. For this reason it is important to avoid using them on plants until after the plant has stopped flowering. If a neonicotinoid must be used on a flowering tree or shrub, it is best to use one that has a lower toxicity to bees like acetamiprid. For more tips on protecting pollinators in the landscape see this link https://extension.entm.purdue.edu/publications/POL-1/POL-1.html .
CATEGORIES OF INSECT AND MITE DAMAGE
Insects can attack and damage plants in 8 different ways. Learning how to recognize these categories will help you develop an effective management plan. Each of the categories has been described in general terms with representative pests indicated in bold type. Details on the biology and control of each of these pests will follow the general description. Please note that the time of insect activity will vary depending on temperature and your location. Times given in this chapter are most applicable to Indiana. Insect activity could occur several weeks later in more northern states and several weeks earlier in more southern states.
- Agents of leaf distortion and discoloration
- Producers of honeydew, spittle, unsightly wax, or insect remains.
- Bumps or swellings on leaves and twigs.
- Defoliators
- Leaf miners
- Borers
- Root feeders
- Agents of disease transmission and rapid decline
(Reader Note: Click on any figure from this chapter and use the right and left arrows to scroll through all figures. You can treat them like flash cards for memorization!)
1. Agents of leaf distortion and discoloration
This group of insects and mites injures plants by piercing leaves and ingesting leaf juices causing them to curl, or discolor. Pests in this category can be separated by how they discolor or distort leaves, the kind of excrement they leave on a plant, and whether or not they produce webs.
Leafhoppers can speckle the leaf surface with white flecks, or they can cause leaves to yellow, curl, or stunt. They feed on fluids in the vascular system of the plant. White flecks are caused by removal of green pigments when feeding on leaves. Yellowing, curling or stunting is caused when damage associated with insect feeding reduces the flow of nutrients and water in and out of leaves.
When plant bugs, like honeylocust plant bug suck juices from expanding young leaves they can kill portions of actively growing tissue and distort leaves. On expanded leaves plant bugs remove the green chlorophyll from leaves, causing them to appear stippled with white spots when the plant bug has removed sap from green leaf tissue that contains chlorophyll. Some species, like four lined plant bug, kill portions of leaf tissue as they feed and leave behind circular areas of brown dead tissue. The liquid excrement of most plant bugs is deposited as a black tar spot that is diagnostic for many pest species. Lacebugs are a distinctive group of plant bugs known for the flat laced wings held flat over their bodies.
Spider mites can cause leaves to become stippled or bronzed when their stylet mouthparts pierce leaf tissue. Most spider mites spin fine webs on the leaf surface where they lay their eggs. Rust mites, like hemlock rust mite, will cause bronzing discoloration without producing webs. Neither of these mites produce honeydew or black tar spots on leaf undersides.
Periodical cicadas and other insects that lay eggs into twigs can kill plant stems and cause leaves to turn brown. Scars formed by the egg laying insect can be used to identify the pest.
Related Pests:
Aphids can curl leaves, distort plant growth or even kill plants. Because they also produce liquid excrement called honeydew they are discussed in the next section. Leaf miners will produce brown areas but are discussed separately because of their unique way of feeding.
Host plants: Many. Primarily a problem on maples. Red maples are most susceptible. Freeman, silver, sugar, and Norway maples are less susceptible to injury.
Damage and Diagnosis: Shoots of trees become stunted, bearing leaves that are curled and brown at the margin (fig. 8). Small, wedge shaped, pale-green adults with white eyes, or spiny yellow eyed immature stages can be found on leaf undersides.
Biology: This pest winters along the Gulf of Mexico and is blown north to the Midwest in early spring when they colonize weeds in nursery rows and crops with green foliage like alfalfa. After these weeds or alfalfa are cut, leafhoppers migrate from dying foliage to maples and other deciduous trees.
Control: Excessive fertilization prolongs shoot growth and increases susceptibility to this pest. Apply a broad spectrum pesticide before leaves start to curl. Pyrethroid insecticides and some insect growth regulators have been particularly effective. Monitor maples for the presence of these lime green leafhoppers on leaves and spray an insecticide when you see an average of one hopper (adult or nymph) per shoot on a tree. Determine the density of hoppers by inspecting one shoot on 4 sides of each tree. Examine the last three leaves of each shoot by slowly turning leaves and looking for hoppers.
Fig 8. potlfeafhopper red maple close up damage
Host plant: Honey locust
Damage and Diagnosis: Leaves of infested trees become distorted, or covered with brown necrotic spots as insects feed on emerging leaflets (fig. 9). Green adults have wings held flat over their body with a head narrower than the first segment of the thorax. Nymphs are spiny. Extensive injury to trees in May or June can cause leaves to drop and may result in the production of a second flush of leaves in June. This puts tremendous stress on these trees, making them more susceptible to honeylocust borer and thyronectria canker.
Biology: With only one generation per year, the honeylocust plant bug spends the winter as an egg on plant twigs. Eggs hatch in spring as leaf buds swell and young nymphs then feed on plants. Nymphs can be found feeding on green buds before leaves have unfolded. Most of the injury is caused by developing nymphs that turn into adults by early to mid-June. Adults lay eggs in June.
Control: It is important to recognize that use of broad spectrum insecticides on honeylocust can kill spider mite predators and promote defoliation by honeylocust spider mites later in the year. To prevent these outbreaks, delay applications of pesticides until you are certain that honeylocust plant bug threatens plant appearance. This occurs only two out of every five years. Treat only when more than one bug is present per leaf when leaves are < 4″ long in the spring. Foliar applications of pyrethroids, can be effective. Soil applications of neonicotinoids are effective, but pollinator protection can be an issue.
Fig 9. honeylocust PBG injury
Fig 10a. Four lined plant bug on prive
Fig 10b. Four Lined Plant Bug Feeding
Fig 11. Lacebug amelanchier
Fig 12a. spider mite on columbine
Fig 12b. Spruce Spider Mite on Arborvitae
Host Plants: Baldcypress, crabapples, fir, hemlock, honeylocust, maples, privet, spruce, yew.
Damage and Diagnosis: Free living rust mites cause green leaves to become finely stippled as they remove small bits of tissue from the leaves. Leaves of heavily infested plants appear faded green, and will drop prematurely. In the right light, the mites appear as white flecks on the surface of the leaf. On baldcypress, leaves will turn brown. Adults, barely visible to the naked eye, are cigar-shaped and resemble tiny light colored maggots, when viewed in the field with a 10 X hand lens. (fig. 7)
Biology: Rust mites are a group of free-living, microscopic, cigar-shaped, mites that feed on plant leaves. They generally winter on stems of woody plants and begin feeding on newly emerging leaves in the spring. Cool season rust mites do best in cool weather and can be problematic on plants such as privet, maples, honeylocust, crabapples, spruce and hemlock. Other species such as baldcypress rust mites thrive in warm weather and tend to be more of a problem in the summer months.
Control: Athough control is rarely needed, it can be achieved with selective products, such as oil, acequinocyl, chlorfenapyr, pyridaben, spiromesefin, or less selective products like abamectin or pyrethroids.
Host Plants: Many deciduous trees
Damage and Diagnosis: When adults lay enough eggs in twigs they can kill them. This is primarily a problem on new nursery stock, and when large numbers of periodical cicadas emerge. Damaged twigs and branches have a series of slits where females have laid their eggs (oviposition). Damage from the periodical cicada is most severe near mature stand of trees where cicadas can complete their long life cycle (fig. 13). Adult periodical cicadas have orange wings with black bodies and red legs. In contrast damage from the annual or dog day cicada is minimal.
Biology: Nymphs of all cicadas feed on roots of trees. Nymphs of annual cicadas feed on roots from 2-5 years and those of periodical cicadas feed on roots for 13 or 17 years before they become adults. Adult annual cicadas are present from mid-July to late summer. After adult periodical cicadas emerge in late May or early June, they fly for 6 weeks. Male cicadas produce a shrill call that is quite distinctive. When periodic cicadas emerge by the thousand, the shrill call of the males to their mates is both distinctive and overwhelming. During the adult flight period adults mate and females lay egg in twigs. Several weeks after eggs are laid a nymph hatches, feeds and drops to the ground to dig for tree roots where they suck on plant sap. Damage associated with root feeding has not been measured and is assumed to be minimal.
Control: Field trials with applications of broad spectrum insecticides show that among available insecticides, pyrethroids can reduce injury from the periodical cicada when applied just before adults emerge. Contact your local Extension service to find out when and if periodical is expected in your area. Discussing the issue with your clients before trees are covered with cicadas will help you better manage the situation.
Fig 13. Periodical cicada adulut oviposit
2. Producers of Honeydew, Spittle, Unsightly Wax, or Insect Remains
Pests in this group secrete substances that clients will readily see in the landscape. Generally speaking, only heavy infestations of these pests threaten plant health. They feed on fluids in the vascular system of plants. Because their food is liquid plant sap, their excrement is a sugary liquid called honeydew. Honeydew can be a problem when large amounts fall from trees down to cars, walks or picnic areas. Areas below trees become sticky, attracting stinging wasps, and ants that feed on the sweet honeydew. In time, honeydew will become food for a sooty mold fungus (fig. 14). This can make the surfaces of leaves, stems and trunk appear as if they have been covered with black soot. Plants in this condition grow more slowly because the mold shades leaves, reducing their ability to capture light used for photosynthesis.
Fig 14. sooty mold tulitpree scale
Scales Insects and Mealybugs
Damage and Diagnosis: Scale insects are small sucking insects that appear to resemble small bumps on leaves and stems. Bumps on twigs and leaves can be caused by either scale insects or gall makers. You can use a flip test to distinguish between galls and scale insects. If you flip over a bump with your thumbnail and tear plant tissue, the bump is a gall produced by the plant in response to a gall making organism. If you flip over the bump and see smooth plant tissue beneath the bump, you probably have a scale insect (fig.15). From the standpoint of control, there are really only 2 kinds of scales. Scales that produce and are covered with sticky excrement (honeydew) are called soft scales. Scales that are not covered with honeydew are called armored scales.
Fig 15. Flipped scales
Fig 16. tuliptree scale
Fig 17. oystershell scale
Fig 18. hawthorn mealybug
- Dormant season oil treatments: Application of 4% oil is most effective for armored scales and mealybugs that winter as immatures or as females that have not produced eggs. This strategy will not work on oystershell scale, or pine needle scales that winter in the egg stage. These treatments are generally NOT effective against soft scales.
- Mid spring treatment to target young adult female soft scales. Applications of bifenthrin during this time can be quite effective at killing soft scales as they lay eggs. It should be reserved for rescue treatment only, since it can flare problems with spider mites.
- Treatment of crawlers with reduced risk insecticides. Applications of 2% oil, insect growth regulators such as pyriproxifen, and spirosefin and spirotetramat can be very effective at this time when crawlers are walking or after they have recently settled. Each species has its own particular time when crawlers emerge. Most, but not all scales, have crawler periods in May. Look for crawlers by either examining twigs with a hand lens, or by tapping a branch over a white sheet of paper. Crawlers vary in color depending on species. They are usually the size of a spider mite. Apply at the tail end of crawler activity to stems and foliage.
- Treatment of crawlers with conventional pesticides. Foliar applications of products such as pyrethroids, acephate, and some neonicotinoids can be very effective at controlling scales. This is your treatment of last resort. It should be used to rescue severely injured trees, especially those with branches that have recently been killed by scales. Application of these materials early in the crawler period will kill crawlers and natural enemies for several weeks. Soil applications of pesticides with systemic activity, like the neonicotinoids can be very effective against honeydew producing scales and their relatives because they feed on liquids moving through the plant vascular system. In contrast systemic materials tend to be less effective against armored scales because they do not exclusively feed on these plant liquids. To protect pollinators, the use of neonicotinoids should be avoided on bee pollinated trees and shrubs, like crabapples, tuliptree, and cotoneaster.
Host Plants: C. heterophyllae is found on pines only. C. pinifolae is found on other pines, fir and spruce hosts.
Damage and Diagnosis: Needles of heavily infested plant are flecked white with scale covers (fig. 19). These two species of closely related scales are difficult to separate in the field. Both species are small elongated (1/8”) white scales attached to needles of evergreens. Scales beneath the covers are purple.
Biology: Individuals of both species winter as either eggs or mated adult females. Individuals that winter as eggs are more winter hardy, and tend to be in the northern part of the Indiana. Those that winter as eggs under scales produce crawlers in May and July.
Those that winter as mated females produce crawlers in June only.
Control Considerations: Several treatments may be needed to control this scale. Dormant oils are only partially effective because many scales winter in the egg stage. To time crawler sprays, inspect branches to determine when the crawler period is ending. Since bees do not forage on pine pollen, an application of dinotefuran can be quite effective.
Fig 19. pine needle scale
Fig 20. Cottony maple scale
Host Plants: Tuliptree, magnolia
Damage and Diagnosis: Orange brown females up to 1/2” in diameter (fig. 16). When females on twigs are swollen with eggs, these orange ridged scales are about the size of a plump currant. Branches of heavily infested trees are coated black with sooty mold. Honeydew begins to accumulate significantly after females mate with males in mid-June. Every few decades (most recently in 2012 in southern Indiana) large areas of the state are afflicted this problem.
Biology: Wintering as second instar on twigs, they resume feeding when the plant comes out of dormancy in the spring. One of the largest soft scales in North America. Females produce up to 3,000 eggs that hatch into black crawlers in late August and September. Crawlers migrate to stem.
Control Considerations: Many natural enemies present. Most susceptible to foliar insecticides during crawler periods in late August. Tuliptree is a favored plant of many pollinators, thus neonicotinoid applications should be avoided.
Host Plants: Hawthorn
Damage and Diagnosis: Tiny white nymphs line ridges in bark and twigs during fall making them appear as if covered with frost. Adults move to twigs and branches. Females swell with eggs (1/8″) and are covered with white wax (fig.18).
Biology: Winters as second instar nymphs on bark and twigs. They resume feeding when plant breaks dormancy in the spring. After eggs are produced, nymphs spend the summer feeding on leaves. Nymphs migrate to bark and twigs each fall.
Control considerations: Many natural enemies including a lady beetle whose larvae superficially resembles mealybugs, but are distinguished the by the presence of teeth. Hawthorn and many other trees and shrubs in the rose family are heavily utilized by pollinators.
Host Plants: Lilac, birch, dogwood, ash, elm, poplar, soft maple, privet, willow, walnut,
Damage and Diagnosis: Small gray or brown scales shaped like oyster shells are present on branches and twigs (fig. 17). Oystershell scale will readily kill branches and twigs that are encrusted with scales. Often, Oystershell scale populations will completely cover the bark of a branch or stem
Biology: Wintering as an egg beneath the scale cover of a female, eggs hatch into crawlers in May and July.
Control Considerations: Dormant period oil sprays are not effective. Summer treatments that target crawlers are a better option for this scale.
Host Plants: Euonymus, pachysandra, bittersweet
Damage and Diagnosis: Leaves of heavily infested plants are covered with the white flecks of elongated (1/16”) male scale covers (fig. 21). Females on stems are brown and resemble oystershell scales, but are half the size and more flattened. Females on leaves are surrounded by halos of yellow in spring.
Biology: Wintering as a mated female on stems, egg laying begins in late May and lasts through early June. Males produce white covers and tend to be more common on leaves than stems. Females tend to be more common on stems than leaves. A second generation of crawlers is produced from late July to early August. Partial third generations occur in some years.
Control considerations: Variegated varieties of euonymus are more susceptible than green. Dormant period oil sprays are quite effective if you can get adequate coverage, as are sprays of insecticides that target crawlers. However, the majority of the population resides on leaf undersides, which makes spray coverage difficult.
Fig 21. Euonymous scale
Aphids
Aphids are generally pear shaped insects, with two visible bumps on the hind end known as cornicles. When wings are present they are clear and roof-like over their body when at rest. Most species are polymorphic, meaning that they can assume a different form at different times of year, on different plants. In many cases this characteristic helps them to take advantage of a good habitat to produce the most offspring in the shortest amount of time. For example, when aphids establish on rapidly growing shoots, they produce wingless daughters who can spend all their time reproducing without mating and feeding without flying to new shoots. As food quality deteriorates, these aphids start producing winged offspring who can fly to better feeding sites. As a group, aphids feed on a wide range of woody plants and have a wide range of life cycles.
Damage potential: Aphids damage plants when they suck plant fluids, injure plant tissues and curl leaves. Most aphids cause only minor damage to the health of the tree and pose more of a nuisance from honeydew secretion. Other aphids like woolly elm aphid cause extensive curling early in the year. Other aphid species like honeysuckle witches broom aphid can distort shoot growth and kill branches (see below). Deposition of honeydew is more of a nuisance over cars and highly trafficked areas because of its ability to attract stinging wasps and coat surfaces with unsightly sooty mold.
Control:
Cultural – Trees such as crabapples, and tuliptree poplar are susceptible to aphids for most of the year. They should not be planted where honeydew is likely to be noticed or cause a problem. Avoid planting these trees near picnic and parking areas. Keep plants well watered and properly fertilized. Over fertilization can prolong aphid infestation by stimulating shoot growth.
Biological – Natural enemies of aphids are abundant in midwestern landscapes. These include predaceous insects such as lady beetles, flower flies, lacewings, small parasitic wasps, and several fungal diseases. Note that parasitized aphids are brownish and swollen, appearing much like a kernel of puffed grain. Conserve natural enemies by avoiding or delaying pesticide applications when possible to allow the number of beneficial insects on your plants to increase. When insecticides are needed, avoid using long lasting broad conventional pesticides when natural enemies have been detected. Application of reduced risk insecticides like insecticidal soaps or summer oils can kill large numbers of aphids while allowing natural enemies to re-colonize aphid infestations after these materials have dried.
Chemical – Dormant applications of oils can kill aphids that winter as eggs on trees. Applications of soaps and oils can also be effective in the summer months. Broad spectrum contact insecticides can kill more aphids than soaps or oils but may foster outbreaks of spider mites later in the season. Applications of pesticides are most effective before significant leaf distortion has taken place. Foliar applied systemic insecticides (e.g. spirotetramat, or acephate) are required after this time to allow the pesticide to reach and kill aphids hidden beneath curled foliage. Soil applications of neonicotinoids are effective, but pollinator protection can be an issue.
Host plants: Apple, crabapple, cotoneaster, hawthorn, mountain ash, pear, quince
Damage and Diagnosis: Curls actively growing shoots and creates a honeydew nuisance. Continues through late July when leaf growth stops. Winged females have a black head and thorax and a green body. Males are wingless. All wingless forms are light green (fig. 22).
Biology: Wintering as an egg on twigs this aphid hatches into inconspicuous nymphs that become noticeable in late May. Aphids remain on same host until populations build. Winged females will fly to find new woody hosts.
Fig 22. Apple aphid on crabapple
Host plants: Tuliptree
Damage and Diagnosis: Yellows leaves in summer and fall, causing premature leaf drop and honeydew nuisance. Feeds only on tuliptree (tulip poplar). Light green aphids and pink aphids are found on leaf undersides. Pink forms tend to be wingless.
Biology: Overwinters as eggs in bark crevices of tuliptree. Eggs hatch to inconspicuous first instars in spring. Winged and wingless forms start to appear in late June. Aphids are present through October.
Host plants: Spring: peach, almond, cherry, and plum. Summer: Over 200 species of herbaceous plants including many vegetables and bedding plants.
Damage and Diagnosis: Extensive curling of leaves on shoot tips during heavy infestations can make trees appear as if they delayed leafing out. Winged adults are light green with black tipped legs (fig.23). Wingless forms of adults and nymphs are pear shaped, straw colored to light green, with a dark stripe along each side and down the back of the abdomen.
Biology: Eggs that winter on the woody host plant hatch into females that produce male and female offspring. Aphids remain on trees for 2 to 3 generations until they fly to an herbaceous plant host where they have multiple generations during the summer. In the fall when the weather starts to cool males and females fly to woody plant hosts. After mating, females lay overwintering eggs on twigs.
Fig 23. Green Peach Aphid Adult
Hosts: American elm and serviceberry
Damage and Diagnosis: Leaves of American elms appear tightly curled, and contain waxy adelgids. Adults are somewhat purplish when wax is removed.
On serviceberry woolly aphids are found on stems in mid-summer (fig. 24).
Biology: This species overwinters as eggs on elm bark, each hatches into a female that produces up to 200 young females without mating. These females and their young produce a second generation that curls leaves and produces young that cause elm leaves to curl. Winged forms produced in this and the following generation during early summer will fly to serviceberry, where they lay eggs that hatch to nymphs that crawl down to feed on tree roots. After several summer generations, a winged generation returns to feed on elms.
Related pest species: Their are several species of woolly aphids in the genus Eriosoma that use Elm as their overwintering hosts. Most notable are the woolly apple aphid, Eriosoma lanigerum (Harris) that feeds on the roots of apples ,crabapples, and mountain ash and the leaf curl ash aphid, Prociphilus fraxinifolii (Riley) that feed on ash.
Fig 24. Wooly elm aphid
Host plants: Honeysuckle
Damage and Diagnosis: New growth of plants is stunted (fig. 25) and twigs become branched into clusters called witches’ brooms. These brooms are easily detected in winter or summer. Cream colored aphids are found between folded leaves in summer. Affected branches die in winter. Heavy infestations can kill plants. The spring generation is winged. The summer generation has winged and wingless forms.
Biology: Eggs that winter on branch tips hatch into wingless females in early May just before leaves unfurl. Once leaves are out, aphids start feeding on leaves. Females from overwintering eggs produce males and females that have multiple generations throughout the summer.
Resistant host varieties: Arnold’s Red, Clavey’s Dwarf and Emerald Mound.
Fig 25. honeysuckle witches broom aphid symptom
Adelgids
Most of the insect species in this group will produce a white wax at some point in their lives. Some species attack conifers an others attack deciduous trees. Some species will produce galls (see producers of bumps on twigs). The biology of adelgids and the general control strategy is similar to that described for aphids. Like with aphids, the principle control strategy for this pest is the conservation of the many natural enemies in the landscape. For the purposes of identification, it is important that unlike aphids, adelgids lack cornicles on their hind end. Many adelgids have complicated life cycles that require several different host species.
Host Plants: Primarily white pine, and to a lesser extent Austrian and Scotch pine.
Damage and Diagnosis: White cottony masses are present on the trunk and under main branches of infested trees (fig. 26). Does not cause significant harm to tree health, but is unsightly.
Biology: This insect has three to four generations a year on white pine. It winters as an immature under white cottony mass. Eggs are laid in early spring and hatch in late April. Some confusion exists about the biology of this pest. There have been reports that this species requires spruce as an alternate host.
Control: Because of the many natural enemies of this pest and its inability to greatly harm tree health, it is best to rely on methods that conserve natural enemies. These include using insecticidal soaps, or oil, insect growth regulators as well as knocking off these adelgids with a high pressure jet of water. Soil applied systemic insecticides, like imidacloprid and dinotefuran are also effective. Dinotefuran may be applied as a trunk spray.
Fig 26. Pine Bark Adelgid Trunk Banding
Spittlebugs
Spittlebugs are closely related to the plant hoppers discussed previously. As such, they have sucking mouth parts that allow them to penetrate plant tissue and feed on plant phloem. They are easily detected by the frothy spittle produced by nymphs (fig. 27). Spittle keeps nymphs in a moist environment and hides them from some natural enemies. Infested shoots appear as if someone had spit on a branch. Spitlebugs are commonly found in many perennial beds. Some spittlebugs, such as the Saratoga spittle bug, Aphrophora saratogensis (Say), are important pests for Christmas tree producers, but are not likely to be encountered in the ornamental landscape. For the nursery and landscape industry, spittlebugs are a nuisance problem because spittle is usually noticed by clients well before enough spittlebugs can be present to affect tree health. Treatments are often applied to trees owned by clients who are repulsed by the appearance of spit on their trees.
Fig 27. Spittlebug Scotch pine
Host plants: Pines, spruce, balsam fir, and hemlock.
Damage and Diagnosis: White globs of spittle hiding black headed nymphs on twigs in spring (fig. 27). Twig and branch dieback can occur when high densities of this pest are present.
Biology: This pest spends the winter as an egg deposited in branches and twigs. In spring eggs hatch to nymphs that begin feeding on shoots. Only adults are present in mid-summer.
Control: This pest has a wide variety of natural enemies including several parasitic wasps and some fungal diseases. It is important to conserve natural enemies when selecting a control option. Use of chlorantraniliprole, can be effective. Applications of insecticidal soap or horticultural oil require thorough coverage. Soil applied systemic insecticides, like neonicotinoids are also effective.
Host plants: Black walnut, Grapes, River Birch, Rose, Sumac, Silver and Red Maple, Tree of Heaven, Willow
Damage and Diagnosis: Infested trees are coated with liquid insect excrement called honeydew that accumulates on the trunk and tree base. This liquid turns black as it becomes infested with a sooty mold. Removal of large amounts of plant sap by these insects rob the tree of sugars and dramatically change normal growth processes. Some trees become less able to withstand winter, and fruit quality and flavor can be changed. Liquid excrement attracts stinging wasps that can be a nuisance. Wax covered egg masses can be laid on trunks, fence posts, stone or brick near infested trees (fig 28).
Biology: This insect winters in the egg stage, covered in a faded tan wax that appears cracked by spring. Black spotted nymphs will hatch from eggs and begin feeding and producing honeydew in May. Nymphs grow and molt into two more stages of white spotted black insects. In July after the fourth molt these wingless nymphs are bright red with white spots. Adults are almost an inch long, have grey wings and appear moth-like to the untrained eye. Adults emerge late July who expose brilliant red hind wings while flying short distances on or between trees. Adults will readily attack and feed on a wide variety of plants on the way to trees where they will lay eggs and reproduce. Although current literature suggests that adult females must feed on tree of heaven (Ailanthus altissima) to be able to reproduce, researchers suspect the list of acceptable trees is much broader. Rows of eggs laid in summer are coated with white wax that fades to a muddy gray color in the fall. Eventually the wax cracks by March as the grey color fades.
Control: The spotted lanternfly is a regulated pest that has been detected in Connecticut, Delaware, Indiana, Iowa, Maryland, Massachusetts, New Jersey, New York, Ohio, Pennsylvania, Virginia, and West Virginia. If you purchase or receive any nursery stock, Christmas trees, stone or landscaping material from the infested part of the country, be sure to inspect them carefully for egg masses. Inspect stands of tree of heaven in the summer months for unusually heavy accumulations of honeydew or the presence of the distinctive immature and adult stages of this pest. Ultimately, repeated applications of systemic insecticide will kill adults and nymphal stages of this pest. Scraping egg masses or spraying them with Golden Natural Spray oil can also be helpful.
Fig 28. SLF Adult and Egg Mass
3. Bumps or swellings on leaves and twigs.
This group of insects and mites can cause plants to produce bumps on a tree. Gall makers cause leaves, stems or twigs to swell into characteristic structures called galls. You can distinguish between galls and scales on a plant surface by trying to flip over the bump with your thumbnail. When you flip over scales the plant tissue is undisturbed (fig. 15). In contrast, flipping over a gall will rip plant tissue.
Gall Makers
Damage and Diagnosis: Galls are abnormal growths on plants caused by living organisms, including bacteria, fungi, nematodes, mites and insects. There are hundreds of kinds of galls, each characteristic of the organism that stimulates its growth. These organisms use the galls for food and protection. Plants produce galls to restrict injury caused by the pest placing a barrier between the pest and the rest of the plant. Because galls stay put they are highly visible to other organisms. Some insects colonize galls to share the home made by the gall maker. Other insects penetrate galls to feed on the gall maker itself.
Management considerations: Galls on trees above the ground seldom, if ever, kill a tree. Nevertheless, they are unsightly and can distort plant growth. Two exceptions are the horned oak gall which may cause considerable damage to shade trees, and the Cooley spruce gall that distort spruce. Conservation of natural enemies and a little bit of patience are the most reliable options for long term management.
Cultural control: No one can reliably predict the time it will take to get natural enemies of a gall problem to bring it under control. Physical removal of galls from trees by pruning does get the gall problem out of the trees and may console a client who is having a hard time waiting for the problem to take care of itself. Pruning, however, can be impractical on heavily infested trees. Removal of galls that fall to the ground and those that are in the trees at the right time of year can give you the added advantage of lowering the numbers of gall making pests in the area.
Chemical control: Insects and mites that cause galls are well protected beneath the swollen plant tissue for most of their lives. Because of this, it is very difficult to time insecticide applications to coincide with the brief periods when they could kill susceptible stages of these pests. Solving the problem is further complicated by difficulties in getting adequate coverage for tall trees. This is especially true when applying dormant oil to kill gall forming insects that overwinter outside of their protective gall on twigs and branches. For most galls, except for Cooley and eastern spruce gall, chemical control is ineffective.
Host plants: Silver and red maples
Damage and Diagnosis: Small, wart-like growths on the foliage are red in spring, then turn green and finally black in summer (fig. 29). They occur singly or in clusters and may be so abundant that the leaves become crinkled, deformed and drop early. These galls never cause permanent injury and actually have little effect on tree health and vigor. They do, however, detract from the normal beauty of the foliage.
Biology: Small cigar-shaped mites overwinter in cracks and crevices of the bark as inactive adults. As the buds swell in the early spring, they migrate out to the bud scales.
When the buds open, mite feeding causes the newly developing leaves to form galls. Mites live, feed, and mate inside galls all summer. In the fall, mites move back to the bark before leaves drop.
Control: Since this gall maker spends the winter as an adult on the tree, keeping old galls around will not contribute to future gall problems and may conserve natural enemies.
Fig 29. Maple bladder gall
Host Plants: Ash
Damage and Diagnosis: Groups of brown, dried galls are seen on trees in summer and winter (fig. 30). Galls deform male flowers, surrounded by a fringe of disfigured green leaves in spring and early summer.
Biology: Green ash is commonly attacked by this small cigar shaped mite that spends the winter as an inactive adult in the bud scales. Adult mites feed on flower buds as they begin to emerge in spring. This feeding causes the formation of groups of galls surrounded by a fringe of disfigured flowers. As galls dry mites migrate to new flower buds.
Control. Adult mites are most susceptible to dormant applications of oil, carbaryl, or a pyrethroid when they become active in spring prior to bud break. In areas where emerald ash borer is present you should shift your focus to protecting ash trees from EAB to keep trees alive.
Fig 30. ash flower gall
Host Plants: Oaks, especially pin oak
Damage and Diagnosis: This tiny wasp gall maker causes trees to produce large numbers of woody galls up to 2 inches in diameter around the stems of pin and willow oak trees (fig. 31). These galls will girdle and cause significant branch dieback.
Biology: Female wasps emerge from woody galls in early spring (April) and lay eggs into the swelling leaf buds. Eggs hatch into larvae that cause a blister like gall along the veins superficially resembling the vein pocket gall of pin oak. In summer (June) adults fly from leaf galls and lay eggs into twigs. The resulting galls become visible the following spring and finish development in about 3 years. Dogwood borers may also feed in young woody galls.
Control. Remove young expanding twig galls as soon as they are visible in the spring. Cutting off old dried galls is not necessary. Applications of insecticides can kill leaf galls, but do not reduce the number of new stem galls produced. Prospects for effective control are difficult, at best.
Fig 31. horned oak gall
Host Plant where galls produced: Spruce
Alternate Host Plant with no galls produced: Douglas-fir
Damage and Diagnosis: This cone-like gall is produced on the tips of new growth of Colorado blue, Sitka and Engelmann spruces (fig. 32a). The gall is green or purplish in color, 1 to 2 inches long, 1/2 to 3/4 inches in diameter and resembles a small pineapple in an early stage of development. Galls turn brown and are easily visible in winter. On Douglas-fir, needles become twisted and yellowed (fig. 32b).
Biology: This insect takes two years to complete its life cycle on Douglas-fir and spruce. Winged adults fly from Douglas-fir to spruce in late July. Adults lay eggs on spruce that hatch into nymphs that spend the winter on spruce twigs. Nymphs become active on spruce in early spring just before the buds break. They develop into adults in May that lay eggs on twigs. When these eggs hatch, nymphs crawl to the base of spruce needles and cause them to produce the characteristic galls. In mid-summer, galls on spruce open to release winged adults that fly to Douglas-fir to lay eggs. These eggs hatch into nymphs that overwinter on Douglas-fir. After bud break, nymphs become active and start to distort leaves. They develop into wingless adults in May. These adults produce offspring that become winged, and wingless adults in July. Wingless adults remain on Douglas fir and winged adults fly to spruce to complete the cycle.
Control on Spruce: The presence of old galls on spruce in the winter suggests that infested Douglas-fir are near enough for adelgids to have laid eggs on spruce the previous summer. Scout spruce to target trees that need treatment. Apply conventional insecticides to the plant just prior to budbreak to kill nymphs that wintered on the plant as eggs. By killing these nymphs you prevent adults from laying the new generation of eggs on young needles, where galls are formed in late May. Conventional foliar applied insecticides, or soil applications of neonicotinoids applied in the fall are effective in preventing galls during the spring.
Control on Douglas-fir: Look for signs and symptoms that nymphs are present on twigs. Early signs include the production of waxy fibers by young nymphs. Later in spring needles begin to twist and yellow. Applications of insecticidal soap or oil, or conventional foliar applied insecticides can effectively control the nymphs and prevent further twisting. Conventional foliar applied insecticides, or soil applications of imidacloprid or dinotefuran in early spring are also effective. Neonicotinoid accumulation in the leaves allows may allow effective control for multiple years.
General control comments: Do not interplant spruce and Douglas fir, since they are alternate hosts of the Cooley spruce gall adelgid.
Fig 32a. Cooly Spruce Gall on Spruce
Fig 32b. Coole Spruce Gall on DougFir
Host Plants: Norway, white, black and red spruce
Damage and Diagnosis: A pineapple-shaped gall (1/2 to 1 inch long) is produced at the base of the new shoot growth (fig. 33). Heavy infestations can distort shoot appearance.
Biology: Like Cooley spruce galls, these also open in mid-summer to release the adelgids inside. However, the adelgids remain on the spruce. Greenish, immature females overwinter in cracks and crevices at the base of the buds. In the spring, the eastern spruce gall adelgids mature and deposit eggs under a mass of cottony threads. These eggs hatch about when the buds open and the new needles are exposed. When nymphs begin feeding, plants produce bulbous galls containing many cells filled with the immature adelgids.
Control of eastern spruce gall makers: Scout for last year’s galls in the dormant season to target plants that need treatment in the spring. Apply broad spectrum insecticides to plants just after bud-break to kill nymphs that hatch from cottony egg masses at the base of needles. Soil applications of imidacloprid or dinotefuran applied in the fall or spring are effective in preventing galls during the spring.
Fig 33. Eastern Spruce Gall Adelgid Spruce
4. Defoliators
Insects in this group consume entire leaves or leaf parts. Patterns of defoliation can help to identify the pest. Some insects like eastern tent caterpillar, spongy moth or yellow neck caterpillar consume the entire leaf with the possible exception of the midrib. Other insects skeletonize leaves by feeding only on tissues between leaf veins (fig. 34). This is characteristic of insects with small mouth parts including many young caterpillars, sawflies, and beetles that feed on older leaves where eggs have hatched. Black vine weevil adults and their relatives leave angular notches on the leaf margin (figs.71,72). Circular scars are cut along leaf edges by leaf cutter bees (fig. 50).
Fig 34. Defoliation
In addition to the pattern of defoliation, the presence and location of webs are useful diagnostic tools to distinguish between some caterpillar defoliators. For example, eastern tent caterpillar produces dense webs where branches join the center of a tree, while fall webworm produces large loose webs on the ends of branches. In contrast, webs produced on the ends of honeylocust branches by the mimosa webworm fold leaves together. The bagworm caterpillar simply covers itself with a small silken web and cut leaves.
Effects of defoliation on plant health
In addition to the effects of defoliation on plant appearance, clients are often concerned about the effects of defoliation on plant health. Complete defoliation during a single season is not likely to kill a tree unless it was severely weakened by some other set of factors prior to defoliation. Many trees defoliated by early season pests (before July 1) will produce a new set of leaves. In the process trees consume an enormous amount of energy that they would normally store in stems and roots for later use. After defoliation, plants are usually less vigorous and more susceptible to diseases and boring insects that thrive on weakened trees. Repeated and consecutive defoliation further weakens trees, killing them outright, or causing them to be too weak to withstand the attack by other insects and diseases. Research on the spongy moth indicates that healthy trees can survive 2-4 consecutive years of losing more than half of their leaves.
As with most insect pests, insecticides are more effective against defoliators when they are immature and small. This is even more important for insects whose webs can hide them from pesticide sprays. To emphasize the difference between management strategies for these two groups of pests, defoliators are divided in two groups, exposed and concealed.
Caterpillars
Caterpillars are the worm-like immature stages of butterflies and moths. This is the stage of moth that will defoliate trees, mine leaves (see leaf miners), or bore beneath tree bark (see borers). Adults feed on nectar of flowers. This stage is most susceptible to control with insecticide.
From a control perspective, it is important to try to kill caterpillars when they are still small. To prevent late season outbreaks of spider mites, early season caterpillars should be controlled with reduced risk or biopesticide like Bacillus thuringiensis, ‘Kurstaki’ (BT), spinosad (Conserve), or chlorantraniliprole (Acelepryn), or any of a number of insect growth regulators diflubenzuraon, or tebufenozide. If you choose to use BT, it is critical be sure that your worm-like specimen is a caterpillar and not a sawfly. Caterpillars are distinguished from sawflies by having 2-5 pairs of prolegs capped with small barbs, called crochets (figs. 5, 46). Sawflies have 6 or more pair of prolegs.
Concealed Caterpillars
Many moth caterpillars attempt to hide from bird predators and other natural enemies by covering themselves with a combination of webbing, excrement, and leaves. This covering can simplify mechanical control of this pest. When isolated webs or overwintering forms of these defoliators are detected you can prune them out of the tree and reduce the need for spraying insecticides. Unfortunately, these webs can greatly complicate control of these pests with pesticides. If you choose to control the young caterpillars with BT, you must apply materials before they are deeply embedded in their web and leaf covering. Other products described to control exposed caterpillars, and pyrethroids are still effective after some webbing has been produced. Note that pyrethroids can cause spider mite outbreaks when applied early in the year.
Host Plants: Honeylocust, Mimosa
Damage and Diagnosis: Leaves on ends of branches become webbed together and turn brown as lime-green caterpillars skeletonize leaf tissue (fig. 35). Heavily infested trees appear frosted brown. Larvae drop to the ground from the trees on silken strands just prior to pupation and can annoy pedestrians. Each silk covered pupa superficially resembles kernel of puffed rice. Masses of pupae can be found in bark crevices as well as glued onto structures under shingles, windows, and door frames in from October through May.
Biology: Pupae winter in sheltered areas. In early June, adults emerge and lay eggs on trees. First webs can be seen on ends of branches in mid-June. Larvae take three weeks to turn into pupae. The second generation of adults fly and lay eggs from late July. Caterpillars are out in early August and start dropping from trees to pupate at the end of the month.
Control: The main goal is to control the problem without killing the predators of honeylocust spider mite that can cause a different problem. Target the first generation of caterpillars to prevent serious defoliation by the second generation. Second generation caterpillars are more numerous and hatch over a longer period of time than the first generation. This makes it more difficult to effectively time pesticide applications.
Look for early signs of webbing before leaves turn brown. These webs are first found in tree tops. Take advantage of urban structures such as parking garages to get a good look at the tops of these trees when you inspect.
Fig 35 Mimosa WWdmg Locust Leaves
Fig 36. Fall Webworm forest edge
Fig 37. Fall webworm adult and eggs
Host Plants: Flowering fruit trees
Damage and Diagnosis: Caterpillars form webs or nests in central crotches of trees (fig. 38). Caterpillars are dark in color with a white stripe on their backs. They defoliate trees in April and May. This early season defoliation is not likely to kill the tree. In early May, large (up to 2″) caterpillars wander from trees to look for a site to pupate (fig. 39). The sight of caterpillars roaming across pavement, patios, or back yard lawns can upset clients. Egg masses wrapped around twigs are easily found in winter when leaves are not on trees.
Biology: Egg masses winter on twigs. Eggs hatch when cherry leaves unfold. Caterpillars crawl to a tree crotch and start to form webs. Caterpillars remain in webs during the day to avoid predation from birds. At night, caterpillars crawl from the mass of webs to feed on leaves.
Control: When possible, mechanical control is preferred. Look for egg masses in the winter and remove them. In the spring, you can easily remove the tents containing caterpillars during the day with a gloved hand. Kill the caterpillars by dropping them in a bucket of soapy water. When many nests are present, or hard to reach, insecticides listed above will provide better control. Avoid the use of pyrethroids on this early season defoliator. Burning nests will cook plant tissue and kill large parts of the tree.
Fig 38. eastern tent caterpillar crabapple webs
Fig 39. Eastern tent caterpillar
Hosts: Many evergreen and deciduous trees. Commonly arborvitae, juniper, false cypress, spruce, fir, pine. Occasionally honeylocust, and Japanese maple.
Damage and Diagnosis: Caterpillars live in silken “bags” covered with leaves of the host plant (fig. 40). Young caterpillars (1/4″) are difficult to see because the leaves that cover them are fresh and resemble the rest of the foliage (fig.41). In early stages of infestations leaves appear to be walking. As infestation progresses, defoliation becomes more apparent. Entire trees can be stripped of foliage. Large bags (up to 2.5″) are easily visible in winter, and superficially resemble Douglas fir cones.
Biology: Early in June, when northern catalpa begin to bloom, the insects hatch from eggs which spent the winter in the old bags attached to tree branches. Caterpillars crawl out of the bag hanging from silken threads until they either reach a leaf or are blown to another tree by the wind. They start to spin their bags that they cover with leaves as soon as they begin feeding. The caterpillars poke their heads out of the bag to feed on leaves. Bags are enlarged as caterpillars grow. If disturbed, they retreat safely inside, and it is almost impossible to pull them out. Each female bag can produce up to 1,000 bagworms. Winged males emerge in August to mate with females that never leave their bag. Eggs are laid in the bag in the fall.
Control: Look for overwintering bags on plants. Physically remove them before egg hatch and drop them in to a bucket of soapy water to kill them. When bags are too numerous or too high in the tree to remove insecticidal control is preferred. Avoid the use of pyrethroids to prevent outbreaks of spider mites. Insecticidal control is most effective during the growing season on small bags (<1″). Cool weather in late May and June can stretch out the period of egg hatch to a month or more. Be sure to check infested sites for bagworms again in July when this weather pattern is present.
Fig 40. bagworm on arborvitae
Fig 41. Bagworm young
Exposed Caterpillars
Host Plants: Many trees and shrubs, especially oaks, apples, birch, mountain ash, willow, and quaking aspen. Lists of resistant species are available.
Damage and Diagnosis: Infested trees can be completely defoliated by hairy caterpillars growing up to 2 ” long. Although many deciduous tree species will leaf out again, complete defoliation two to three years in a row can kill a tree. During heavy infestations, the accumulation of caterpillar excrement below trees can become a nuisance.
Mature caterpillars, present in June are dark with 6 pair of red and 5 pair of blue spots along their backs (fig.42). Occasionally, outbreaks of spongy moth can coincide with forest or eastern tent caterpillars. Forest tent caterpillars can be easily distinguished by white “key-hole” markings along the top of their backs. Eastern tent caterpillars have a white stripe along the top of their backs and produce conspicuous webbing. Proper identification of spongy moth is critical for planning management strategies. Spongy moth pupae can be found on trunks or on other structures in late June to July. White adult females can be found laying light brown egg masses from mid to late July through early August.
Biology: Egg masses containing from 50 to 1500 eggs (fig. 43) can be found on tree trunks and nearby sheltered areas including door jams, picnic benches, firewood, under vehicles, and at the bottom of nursery containers. Eggs hatch in late April into black caterpillars that climb to the top of a tree or structure so they can be blown by the wind to a new tree. When the caterpillars land on a tree they begin feeding on leaves. As caterpillars become large, they feed only at night. When full grown in late June, caterpillars will wander to sheltered areas to construct pupae. In mid July, white female and brown male moths emerge. Adult female spongy moths do not fly. They sit on trees and release a scent that attracts males. After mating, females will walk to find a sheltered place to lay eggs.
Control: These exposed caterpillars are easily killed by reduced risk products mentioned above. Most conventional insecticides can readily kill caterpillars while they are feeding. Spongy moth can often be an emotional issue for a community because the infestation can be widespread. When found outside the generally infested part of Indiana, the Indiana DNR Coordinates control efforts that can include the use of sex pheromones to disrupt mating, or applications of Bacillus thuringiensis. Please see the Spongy Moth in Indiana Home Page for details http://extension.entm.purdue.edu/GM/.
Fig 42. Spongy moth caterpillar
Fig 43. Spongy moth adult laying eggs
Order and Family: Lepidoptera: Notodontidae
Host Plants: Most deciduous trees.
Damage and Diagnosis: White egg masses, each with up to 100 eggs are easily visible on leaf undersides. Young caterpillars will first skeletonize leaves, and then strip them of foliage as they mature. Younger larvae are brick-brown with yellow stripes along the body. Older larvae (fig. 44) are black with yellow stripes and up to 2 ” long. Late season defoliation does not significantly harm tree health, but can be unsightly.
Biology: After spending the winter as pupae, adults emerge in June and July and to lay egg masses on leaf undersides. Eggs hatch in late July into caterpillars that feed in groups through August. Large caterpillars pupate in the soil where they spend the winter.
Control. Look for young caterpillars in July and treat before caterpillars become large and cause major damage. Though late season defoliation is unsightly, it does minimal harm to tree health because it occurs close to the time of normal leaf drop.
Fig 44. Yellownecked catepillar
Sawflies
Damage and Diagnosis: Sawflies are thick-waisted wasps. They are called sawflies because adults have a “saw-like” ovipositor that they use to insert eggs into plant tissue.
Their immatures are worm-like and resemble caterpillars. They have six or more pair of prolegs that lack basal hooks called crochets. On some sawflies, like pear slug described below, the prolegs may be difficult to distinguish.
Some sawflies like European pine sawfly and mountain-ash sawflies will feed in groups that can be particularly destructive. These have the distinctive behaviors of moving in groups and regurgitating when disturbed. Spinosad, (Conserve) kills sawfly larvae, but Bacillus thuringiensis does not.
Order and Family: Hymenoptera: Diprionidae
Hosts: Scotch, Austrian, and Mugho pine.
Damage and Diagnosis: Damaged branches have old needles removed. New growth on old branches resembles a mule’s tale. In early spring you can see scars where eggs were laid on needles during the previous fall (fig.45). Young larvae are dark green and difficult to see. Needles consumed by young larvae resemble slender brown straw. As damage accumulates, more straws become visible on branches. Late instar larvae grow to one inch and are dark green with a black head and black longitudinal stripes (fig.46).
Biology: After larvae become about 1″ long, larvae pupate in brown pupal cells (1/2″ long) that can be found along the trunk or on the ground. Adults emerge in the fall and lay eggs in needles (fig.4). First chewed needles are visible in mid- to late April.
Control: Sawfly larvae are easily killed by most broad spectrum insecticides, spinosad (Conserve), insect growth regulators, botanicals, or insecticidal soap or oil. Most effective control is achieved when pesticide is applied early in the season when sawflies are young. After sawflies are one inch long they stop feeding and construct pupae. Applications of insecticide at this time are no longer needed.
Sawflies regularly suffer from a lethal virus-like disease that greatly reduces their number. If you notice larvae that are hanging limp from pine needles there is no need to apply an insecticide. This virus-like disease is not likely to be commercially available in the near future.
Fig 45. Young European pine sawfly egg and neonate
Fig 46. Old European pine sawfly
Fig 47. Pear slug sawfly
Beetles
Beetles are a very diverse group of insects that share the common characteristic of having hard or leathery forewings. These forewings, known as elytra, can be brightly colored or plain. Although lady beetles eat insects and not plants, their orange or redspotted forewings are a good example of brightly colored elytra. Immature beetles are called grubs. They lack prolegs and do not resemble caterpillars or sawflies. The grubs of some beetles (e.g. weevils, longhorned beetles and metallic woodborering beetles) have no legs. Unlike caterpillars and sawflies, both adults and immatures, can damage plants.
Fig 48. Japanese beetle skeletonization
Beetles can skeletonize (fig. 48) leaves or consume entire leaf portions. Leaf notching (figs. 71,72) is a distinctive type of defoliation caused by black vine weevils and their relatives. These beetles remove tissue from the leaf edge and leave a characteristic notch. Controls for beetles can be directed against adults, grubs or both stages.
Order and Family: Coleoptera: Scarabeidae
Host Plants: Many deciduous trees and shrubs especially linden, birch, sassafras, sycamore, Norway maple, birch, elm and flowering fruit trees.
Damage and Diagnosis: Leaves become skeletonized, with all tissue removed between leaf veins (fig. 48, 49). Adults have copper colored wings and a green pronotum. Adults can be found during the day feeding in large groups on leaves or fruit.
Biology: Winters as late instar grubs in soil, where they feed on plant roots. This stage is more commonly known as one of the many white grubs that attack turf. Adults pupate in late May or early June. Adults emerge to feed on trees in late June, with peak densities occurring around July 1. Adults can be seen flying until early August. Eggs, laid underground, hatch into the larval stage during the first week of August. Grubs feed on roots until weather cools in October when they move down into the soil.
Control: When infestations are low, applications of azadirachtin can repel adults. Apply a broad spectrum insecticide, such as carbaryl to leaves when beetles are seen feeding on trees. These beetles will be around for about six weeks. Most materials will only kill beetles for 4 to 5 days. Pyrethroids like deltamethrin provide longer control up to 10 days. Repeat insecticide applications when needed to reduce further injury. Do not use Japanese beetle traps to control these beetles. Traps bring more beetles and damage to the area. Resistant varieties of crabapples are available.
Fig 49. Japanese beetle adult
Bees
Host plants: Removes foliage from a wide range of trees and shrubs early in the season. Redbud is commonly attacked.
Damage and Diagnosis: Circular scars are present along the leaf margin (fig. 50). Do not confuse with the irregular leaf notches caused by black vine weevil (below). Adults are about the size of a honeybee, but dark with rows of white hairs on the abdomen.
Biology: Adult females stand on the edge of leaves and cut a circular scar as they remove a leaf disc. These discs are used to construct nests. Typically, an adult female will pack a tunnel with cells containing eggs and regurgitated pollen and nectar as food for her young. Each cell is separated by plug made of leaf discs that the female removes from plants.
Control: Injury from these bees is more a curiosity that a problem. Although circular scars detract from plant appearance, the injury is not likely to affect plant health. Advise your clients that these bees are beneficial because of their ability to pollinate plants. If your client is persistent you can prevent further injury to plants with a broad spectrum insecticide at the first sign of scarring in the spring.
Fig 50. Leaf cutter bee
5. Leaf miners
Damage and Diagnosis:
Insects in this group feed between the upper and lower surface of a leaf as immature larvae. This process, known as leaf mining, discolors leaves in a characteristic pattern. Serpentine leaf mines are shaped like a snake. Blotch mines form an irregular blotch with no particular shape at all. Mines can be caused by the immature stages of beetles, flies, wasps, and butterflies. Mines can be distinguished from leaf scorch by holding a leaf up to the light and looking for the silhouette of the larva and the black excrement (fig. 51).
Fig 51. Leaf miner visible through light
Control:
Biological – Like galls and scales already described, insects that cause these mines are easily found by natural enemies that feed on them. For a variety of reasons, including weather, host plant variety, and pesticide use, leaf miners often outstrip the potential of natural enemies to keep them under control.
Chemical – Systemic insecticides provide the most reliable control of leaf miners because they are able to deliver the pesticide directly to the insects beneath the surface. Applications must be timed so that the insecticide gets to the larva when the larvae are still small and before extensive mining disrupts the movement of systemic material within the leaf.
Learn the life cycle of the leaf miner you want to control so you can properly time insecticide applications. Success with some of the soil applied systemic insecticides like neonicotinoids, and chlorantraniliprole, requires applications at least 4 weeks before adults lay eggs. If you choose to use neonicotinoids be sure to take steps to protect pollinators on wind pollinated trees such as hawthorn, American holly and boxwood. Foliar applications of systemic materials like acephate, chlorantraniliprole, or spinosad, should be applied soon after egg laying scars are visible. Controls for some leaf miners, such as those attacking birch and hawthorn are only effective if applied before the first generation mines in the spring. In this case you will have to tell your client there is nothing you can do until the following year. Clients seeking revenge against these leaf miners must be advised that late season controls will not solve the problem.
Order and Family: Hymenoptera: Tenthredinidae
Host plants: Birches, especially gray, Betula populafolia , paper, B. papyrifera., and European white, Betula pendula.
Damage and Diagnosis: Infested leaves have one or more brown irregular shaped blotch mines (fig. 52). Heavily infested trees with most of the leaves infested appear scorched brown. Young mines produce round circular halos of discoloration that are especially visible when leaves are held into the light. Larvae are orange. Egg laying produces smaller but still visible halos when looking at leaves in the light. Adults are small (1/4″) black sawflies.
Biology: Pupae spend the winter in soil at the base of infested trees. Adult sawflies fly to leaves in early May about one week after leaves unfold. Eggs are laid into young leaves. Larvae mine leaves for 2-3 weeks until they chew a hole in the leaf and drop to the ground to pupate. There are 3 to 4 generations a year.
Control: Look for adult activity and egg laying scars on trees soon after leaves have unfolded to time foliar systemic spray. Soil applied systemic insecticides should be applied in the fall to kill leaf miners during the following spring. Birches are wind pollinated, so insecticide treatments will not harm pollinators.
Fig 52. birch leafminer dmg
Order and Family: Coleoptera: Curculionidae
Host plants: Elms.
Damage and Diagnosis Infested leaves have either one or more brown areas produced by leaf mines feeding inside the leaves. Leaves may also be peppered with holes in early spring and in late summer (fig. 53). From a distance, the accumulation of holes can give a tree a faded appearance.
Biology: Adult beetles overwinter in the leaf litter and begin flying in search of elm leaves that have just emerged from their buds. Eggs laid in leaves produce the grubs which make June mines. Adults emerge from leaves and feed on leaves until they overwinter. There is one generation per year. This insect is more of a problem on newly planted trees where foliage is low enough to the ground for injury to be noticed. As trees get older and larger the small holes in the leaves and leaf mines are difficult to detect in the vigorously growing trees. This pest is unlikely to harm the health of larger trees.
Control: Soil applied systemic insecticides (imidacloprid) should be applied in the fall to kill leaf miners during the following spring. Spring applications of imidacloprid or dinotefuran reduce, but do not eliminate injury, when they kill leaf miner grubs and adults. Foliar sprays of broad spectrum insecticides like a bifenthrin or carbaryl directed against adults in spring can reduce mine formation. Elms are pollinated by wind, not bees.
Common leaf miners not mentioned include, hawthorn leaf miner, native holly leaf miner, locust leaf miner, and boxwood leaf miner. Each miner feeds on plants associated with its name.
Fig 53. Elm Flea Weevil
6. Borers
All pests in this category feed beneath the bark of a tree as larvae. Some of these pests feed as larvae and adults. Although there is some overlap, these pests are divided into 4 categories based on how they feed as an adult or on the part of the tree where they feed. Twig chewers scar or girdle a twig when adults feed on the twig surface. Twig or leader borers kill twigs and leaders when adults feed, or when eggs laid on this part of the tree hatch into larvae that bore into the stem until they develop into adults. Large limb and trunk borers lay eggs on the limb or in crevices of the trunk surface that hatch into larvae that feed beneath the bark surface until they develop into adults. Bark beetles, mate at or near the bark surface, and adults lay eggs in tunnels beneath the bark.
Management Considerations:
Cultural control: When these insects chew on or inside twigs, trunks and limbs, they separate all or part of infested trees from their supply of water and nutrients, killing all or part of these plants. Pests in this group thrive when the tree is under stress. Proper watering, fertilization, and mulching are critical to a good control program. Some pests in this group breed on dead or dying trees. For these pests, sanitation, or the destruction of the dead and dying trees and limbs, is an important tactic for killing borers before they emerge from these plants to attack remaining healthy trees
Chemical control:
Trunk Sprays – Coating the bark and twigs of trees with a long-lasting contact insecticide is an effective way to kill insects that must chew through the bark. Pyrethroids, like bifenthrin and permethrin are quite effective against all borers. Chlorantraniliprole (Acelepryn) is a new insecticide that works particularly well against moth borers and does not cause outbreaks of spider mites and scales. Timing is critical to assure that the pesticide is still active when the insect chews through the bark surface on the way into or out of the tree. Traps are available to help you monitor the life cycle of many of these pests and improve your timing of pesticide applications.
Soil applied systemics – Applications of systemic insecticides to the soil are a common way to kill insects that bore beneath the plant surface. These products should be placed within a foot of the trunk. Please see this YouTube video for a demonstration.
https://www.youtube.com/watch?v=ub5_jzrWVug
Here the strategy is much like that already described for leaf miners. You want the young larvae to feed on poison cambium before extensive damage occurs to the vascular system that blocks the flow of toxicant through the plant. Imidacloprid and dinotefuran, and other neonicotinoids are long-lasting insecticides that are particularly well suited for this type of application. These products are most effective against beetle borers and not moth borers.
Tree injections – Insecticides can be injected into the functional xylem of trees using a variety of techniques that include drilling a hole into the tree trunk. When sufficient product is delivered into the tree these products can be quite effective on borers of deciduous trees. This method of insecticide delivery is best reserved for emergency situations like emerald ash borer, when the life of a tree is at stake. Emamectin benzoate and azadirachtin kills both beetle and moth borers. Please see this YouTube video for a demonstration: how to inject a tree.
https://www.youtube.com/watch?v=U6HL3MJ8JkM
Biological Control: Some pests in this group have been successfully controlled with entomophagous nematodes. Trunks and limbs must be drenched with a nematode solution to allow the nematode to swim through borer holes to the pest below. This method has been most effective against clearwing borers, and root collar weevils whose larvae attack live trees.
Twig Chewers
These insects scar or girdle a twig when adults feed on the twig surface. On conifers, twigs will brown several weeks after adults have fed (fig. 54). On deciduous trees, symptoms appear sooner. Eventually injured twigs fall and clients become concerned. For the most part this injury is unsightly and does not harm tree health. Injury is more damaging to newly planted trees, or when the leader is attacked. Sanitation or coating twigs with insecticide when insects are feeding will prevent damage.
Fig 54. twig chewing weevil injury
Host Plants : Pines, spruce, fir, hemlock, larch, and cedar.
Damage and Diagnosis: Adults chew the twig surface in the fall and spring, causing twigs to ooze sap and turn brown in early summer. Adults are black snout-weevils, larvae are white and legless. Can be a problem in sites where pines line a drive and some trees have been removed and stumps remain. Severe problems occur in Christmas tree plantations and tree nurseries when the leaders of young plants are killed.
Biology: Adults are attracted to cut pine and mate on pine stumps when the weather warms in spring. Females burrow to roots of cut stumps to lay eggs. Larvae feed on these roots until they pupate in chip bark cocoons and emerge as adults in September.
During the summer, adults spend days in leaf litter and nights feeding on the twigs. Adults live for two years and lay eggs during both summers.
Control: Removal of breeding sites (stumps of host plants), or spraying with residual insecticide can reduce the chances for tree injury. Improve timing of sprays by monitoring for the emergence of adults in spring. Place freshly cut disks of pine (2″ thick) on the soil surface in a discrete area near an infested site and check upper and lower surfaces for adults. When adults are found in early spring or fall, apply a broad spectrum insecticide to stumps to kill mating weevils and on live trees to kill adults attempting to feed on twigs. Alternatively, soil applications of neonicotinods in the spring or fall can be quite effective.
RELATED PEST:
This weevil causes similar injury, has a similar life cycle, and control (to Pales weevil Hylobius pales). It is smaller than Pales weevil and has two white marks on its elytra.
Host Plants: Many deciduous trees but not maple. Particularly a problem on oaks and hickory in the Midwest.
Damage and Diagnosis: The adult female girdler chews a ring around the outside of a twig (fig. 55). Leaves on twigs wilt and turn brown after adult female girdled it. Twigs dry and fall to ground in late summer.
Biology: Larvae winter in twigs that have fallen to the ground. In the spring and summer, larvae develop to pupae that emerge as adults in late summer. A mated adult female will lay eggs on the part of twig beyond the ring that she has girdled. The twig that dries and falls to the ground contains the larvae inside that develops to an adult.
Control: Collect and destroy branches that have fallen to the ground. Removal of and destruction of shoots on the tree is not likely to be an effective control, since adults can continue to lay eggs until the weather cools. No insecticides are labeled for this pest.
Fig 55. Twig Girdler
Other twig girdlers:
Other girdlers common on oaks in the midwest include several species of Agrilus spp. whose larvae mine around the twig just beneath the bark surface. Adults of these beetles are metallic wood boring beetles (Family: Buprestidae), and are related to bronze birch borer.
RELATED PEST: Twig pruner
In contrast to girdlers, twig pruners sever the twig when tunneling larvae chewing from the twig center (fig. 56). Symptoms, host range, and controls of twig pruners are similar to girdlers. It is important to note that the biology of twig pruners is not clear, but adults are believed to be active in the spring.
Fig 56. Twig Pruner
Twig or Leader Borers
Host Plants: Pines, especially Austrian, and Mugho
Order and Family: Lepidoptera: Tortricidae
Damage and Diagnosis: Look for dead and “U” shaped terminals present from last years feeding, or hardened globs of pitch at the base of a large bud (fig.57). After bud break, look for fresh sawdust like excrement in infested shoots. Infested shoots should fail to elongate and have short needles. In late summer you should see a few red needles mixed with green needles on a terminal.
Biology: Caterpillars winter in needles near shoot tips that have been mined during the previous summer. In April, caterpillars crawl to shoots and bore through the base of buds into shoots before bud break. There, caterpillars continue to feed and develop into pupae. Adults emerge in late May, and egg hatch on needles is in early June.
Control: Small infestations can be controlled by pruning out shoots. A sex pheromone trap is available to time the flight of adult moths. Target caterpillars entering shoots in the May or eggs hatching in early June with either a pyrethroid spray, chlorantraniliprole spinosad, or Bacillus thuringiensis to kill larvae hatching from eggs. Applications of chlorantraniliprole or spinosad have the added advantage of being systemic and able to penetrate needles and kill young larvae.
Fig 57. European pine shoot moth
This pest causes the same kind of injury as the closely related European pine shoot moth. One generation a year occurs in the northern part of its range and four generations a year in the south. A sex pheromone trap is available to help time insecticide sprays.
Hosts: Pines, especially white pine, Norway, and Colorado blue spruce.
Damage and Diagnosis: Infested trees have the leader curled into a shape that resembles a shepherd’s crook (fig. 58). Lateral branches from the infested tree’s first whorl may also be curled. The top 2 to 3years of growth can be affected. In early summer, legless (1/4″) white c-shaped grubs can be found in stems, beneath the bark surface. In late summer, chip-bark cocoons are formed by larvae at the base of injured stems.
Biology: Adults winter in leaf litter and fly to tree tops to mate when the weather warms in the spring. Females lay many eggs in terminals that hatch into grubs that bore into shoots. Legless larvae continue to feed until July when they pupate in chip bark cocoons. Adults emerge in August and chew on twigs.
Control: Applications of broad spectrum insecticide to tree tops should be timed to kill adults gathering on twigs in early spring (April), or adults feeding on twigs in August. Mid fall (October) or early spring application (March) of imidacloprid has also been shown to be effective Prune and destroy damaged leaders that contain larvae or chip bark cocoons before adults emerge in August. Mixed species plantings of pines are less likely to build damaging numbers of this pest than pure stands of susceptible species.
Fig 58. white pine weevil shepcrook
Large Limb and Trunk Borers
Hosts: Pines, primarily Austrian, and Scotch, and occasionally Douglas fir
Damage and Diagnosis: In the spring, leaders of infested trees wilt and curve downward to resemble a shepherd’s crook or fish hook, much like the white pine weevil (fig. 58). At the base of the leader, however, you may find a greasy looking grayish caterpillar feeding in the whorl. In older trees, wounds caused by these caterpillars are found all along the trunk where branches are joined. Wounds are gummy and covered with white crumbs of caterpillar excrement. Growth above infested terminals is often poor in comparison to healthy trees. Branches joined to the main trunk at infested whorls, or tree tops can be girdled and killed (fig. 59).
Biology: Young, first instar caterpillars winter in a shallow pit that they dig in the bark, the previous fall. When the weather warms in early April, caterpillars crawl out of their resting place along the exposed bark surface to either the tip of the leader, or to where the branches join the central trunk. When it bores into the bud of the leader it chews its way down to the whorl causing the shepherd’s crook. When it bores to where branches join the central trunk it produces the gummy wounds, sometimes girdling or killing limbs or tree tops. Once in the tree, it feeds until it pupates in July. In August, moths emerge and lay eggs on the tree trunk. Young caterpillars feed in bits of bark until they dig their shallow pit where they spend the winter.
Control: Sanitation, or the removal of heavily infested trees can greatly improve your ability to manage this pest. Adult moths will often lay eggs on old wound sites, or nearby trees. Reducing tree stress will also help trees resist attack. Chemical controls with a pyrethroid, or chlorantraniliprole are most successful when applied in early April before the weather warms. This kills the young caterpillar as it crawls from its overwintering sites to bore beneath the bark.
Fig 59. Zimmerman pine moth
Bark beetles on Pines
Order and Family: Coleoptera: Scolytidae
Hosts: Pines and spruce.
Damage and Diagnosis: Limbs and entire trees turn brown (fig. 60a). Large numbers of small holes (> 100 sq ft) and about as thick as a pencil lead are found along the main trunk and major limbs. Peal back bark to reveal engraved areas where larvae tunneled through cambium (fig.60b). Small black beetles and white, legless larvae may be present.
Biology: Beetles winter as larvae in limbs. Adults emerge in late April and attack nearby trees. Many adults carry a blue staining fungus that attacks the plant vascular system. This fungus can be passed to new trees when attacked by the adult bark beetles. In Indiana bark beetles are active from April through September, with adults flying through September.
Control: Sanitation, or the removal of heavily infested trees can greatly improve your ability to manage this pest. Be sure to destroy all wood prior to April 15 to reduce the number of beetles that may be available to attack nearby trees. Apply a pyrethroid insecticide in mid-April to kill beetles attempting to enter or leave remaining trees. Soil applied systemic insecticides (imidacloprid) have been shown to reduce injury from this pest.
Fig 60a. pine engraver beetles
Fig 60b. Pine barkbeetle exit holes
Clearwing borer moths
Clearwing borers are a group of closely related moths that superficially resemble wasps and bore into trees or stems. Key aspects of their biology are summarized below.
Hosts: The common name of pests in this group usually includes that name of the host plant that these borers attack. Common examples include:
| Borer | Hosts attacked |
| Banded Ash Clearwing | Ash |
| Dogwood borer | Dogwood, apple, pear |
| Lesser peach tree borer | Peach, cherry, plum, Prunus |
| Lilac borer | Ash, lilac, privet, fringe tree |
| Oak borer | Oak |
| Peach tree borer | Peach, cherry, Prunus spp. |
Damage and Diagnosis: Injured trunks or branches have loose or pealing bark. Sawdust-like excrement can be seen from holes where borers have attacked portions of the tree that are above ground (fig. 61). Caterpillars beneath the bark are usually creamy white in color. When adults emerge, a brown straw-colored pupal skin is left hanging out of the trunk, or branch (fig. 62). Borers that attack at the tree base or just below the soil line may have excrement pellets and pupal skins hidden from view. Infested trees have dead limbs or twigs (fig. 63). The clear wings, slender bodies and flight habits of adult moths in this group cause them to superficially resemble wasps (fig. 64). Unlike wasps, adult moths lack chewing mouth parts and have bodies that are covered with scales. Adult moths have straw like mouth parts that are used for sucking nectar.
Biology: Late instar caterpillars spend the winter beneath the bark of infested trees. Larvae turn into pupae in the tree bark. Just prior to emergence, the pupae pushes its way out of the bark. When the adult emerges from the pupae it leaves the pupal skin in the branch or trunk. Soon after females emerge, they crawl a short distance on the bark, arch their abdomen and release a scent into the wind. This scent, called a sex pheromone, helps the female find a mate by attracting males who are down wind. After mating, eggs are laid on the bark. Eggs hatch into caterpillars that chew a hole in the bark.
Depending on species moths can have 1-2 generations a year. Oak borers take 2 years to develop into an adult.
Control:
Chemical – Use traps, baited with the sex pheromone of the clearwing moth to time the application of a long lasting broad spectrum insecticide on the trunk and limbs of infested trees. Suggestions include chlorantraniliprole (Acelepryn) and the synthetic pyrethroids, like resmethrin and bifenthrin. Apply the insecticide 14 days after the first male is found in a trap. This coincides with the beginning of the time when most eggs will be hatching and chewing their way into the bark. Traps and baits are commercially available, and usually come with picture identification sheets.
Biological – When using entomophagous nematodes, be sure to apply them with plenty of water when the insect is in the caterpillar stage and the temperature is between 55º and 85º F. In a given generation, most individual clearwing moths should be caterpillars from the last week in August through the first week of May. Moths with a May flight period should be caterpillars only through the first week of April. Moths with two generations a year should be in the caterpillar stage 3 weeks after the peak of the pheromone trap catch.
Cultural – Improper use of plastic trunk wraps can make trees more susceptible to clearwing borers that attack tree trunks. Tightly coiled wraps keep bark moist, and can protect borers from parasitic wasps that normally attack them through the bark surface. Loosely coiled plastic wraps with at least 1/4 inch of air space do not cause this problem.
ROUND HEADED BORERS
Borers in this group are beetles whose round headed larvae produce round tunnels as they feed in the wood (fig. 65). Adults also have long antennae and are commonly called long horned beetles. Tunnels are usually kept clean. Fine wood shavings thrown form tunnels are commonly found on or just beneath the bark surface.
Fig 65. round headed borer hole
Damage is caused by the larval stage of the beetle that consumes the heartwood and weakens limbs until limbs break. Symptoms are hard to see from a distance. Trees need to be inspected up close in order to find symptoms. The larvae, which can reach an inch and half in length, bore underneath the bark and cut off nutrient flow from the tree. Actively infested trees have visible black or brown pits where adults have laid their eggs (fig. 66). Larval feeding beneath the bark can cause areas of the trunk to appear black and weeping with liquid. Adults chew through the bark and emerge from dime sized holes. Adults are distinctly large (1-2 inches long) with a black body, light spots and have long antennae (fig. 67). Look for sawdust-like excrement around large holes to help distinguish from woodpecker holes.
Biology: Adults emerge in the spring and mate after a couple days of feeding on the bark of young twigs and on the tissue around the main veins of leaves. Adults lay eggs in small depressions they make by chewing on the bark. Eggs hatch within two weeks and begin feeding on tree vascular tissue. After a few weeks, the small larvae bore into the heartwood to feed until they reach nearly 1.5 inches in length. There is one generation per year.
Management: Currently ALB is a regulated pest. The current policy of the USDA Animal Plant Health Inspection Service is to eradicate this pest. For this reason, it is possible for your tree to be destroyed by this agency even after you have treated your tree. Therefore, we do not recommend treatment of your trees at this time.
If you find this pest, please report it to local authorities via the beetlebusters homepage (http://beetlebusters.info/) or call 1-866-NO-EXOTIC.
Fig 66. Asian longhorned beetle egg laying scars
Fig 67. Asian Longhorned beetle and holes
Fig 68. black locust borer
Flatheaded borers
The greatly expanded second thoracic segments of their larvae make them appear as if they have a flattened head. These borers produce an oval tunnel when they dig into the wood. Unlike the larvae of clearwing borers, and round headed borers, these insects will pack their excrement in the borer hole. Adults are metallic and are called metallic wood boring beetles. Be aware that Emerald ash borer (fig. 69) is an exotic species that was first reported in North America in Detroit feeding on green ash in 2002.
Fig 69. Emerald ash borer adult
Hosts: True ash trees (Fraxinus spp), White fringe tree (Chionanthus virginica)
Damage and Diagnosis: Early symptoms are present on the upper third of the tree. This included a thinned canopy, the presence of woodpecker holes, and splits in the bark that reveal curvy zig-zag galleries beneath (fig. 70). As tree health declines, trees will also sprout shoots from the sides of branches and trunks. Adult beetles are bright metallic green and difficult to see when they are in the tree canopy feeding on leaves. Adults have rounded bellies and flat backs and are small enough to fit on a penny. Their peculiar shape accounts for the distinctive “D”-shaped exit holes from which they emerge from trees. The bark of heavily infested trees can come off in sheets, revealing the distinctive galleries left by the white larvae that feed beneath the surface. Larvae are recognized by their bell shaped segments and their flattened shape.
Biology: Adults emerge when black locust bloom to feed on leaves and lay eggs on bark. Larvae do the damage by feeding underneath the bark. They will consume every last square inch of available tissue beneath the bark. Trees can be killed in 1-3 years. In late summer, each larva digs about 1/2 inch below the bark surface to turn into a pupa, the transition phase between larvae and adult beetle. Larvae and pupae stay in the trunk all winter until the weather warms in spring. There is only one generation per year.
Control: Canopy decline is the best way to gauge the tree’s health. If at least half the canopy is gone, the tree is not worth treating as its likelihood of survival is very low. Systemic insecticides should be used to treat emerald ash borer via soil applications or trunk injection. Imidacloprid has shown success in saving ash trees up to 20″ in diameter at chest height (DBH). This product is available for purchase in most home garden centers. Professionals can use other products. Dinotefuran can be sprayed to the trunk of trees up to 20 inch DBH. Emamectin benzoate can be injected into the tree and lasts for up to 3 years depending on tree size. It can protect trees in excess of 48” DBH. Applications of each pesticide are most effective in the spring. Azadiractin (Azasol) can be used successfully if injected before symptoms appear. Ash trees are wind pollinated and flower just before leaves open in spring.
Resistant Varieties: Asian Ash species (Manchurian Ash) are resistant. Blue Ash Fraxinus quandrangulata is one North American species that can survive infestation in the forest.
Fig 70. EAB larval galleries
Order and Family: Coleoptera: Buprestidae
Hosts: Frequent: European white birch, Less often: Gray birch,paper birch ,yellow birch. Rarely if ever: River birch, Heritage birch
Damage and Diagnosis: Infested trees have the general symptoms of borer injury, dead limbs, yellowed branches, eventual tree death. Infested trees have a ridged bark, where borers have made their zig-zag pattern under the surface (fig. 71, 72). Holes where adults emerged are “D- shaped”. Adults are coppery brown, with a keel shaped abdomen, and are one of the many species of metallic wood boring beetles.
Biology: Wintering as a late instar larvae in the tree trunk, adults emerge from late May to early June from exit holes and have only one generation a year. Adults fly to the tree canopy and chew small notches on leaves as they feed. Eggs are laid in cracks and crevices, under loose bark on the sunny side of trees, or areas where a tree has been mechanically injured. Adult flight lasts about 6 weeks. Two weeks after they are laid, eggs hatch into larvae that chew into the wood. When you peel off the bark of an infested tree you can easily see the dark brown mounds that zig-zag along the wood where larvae have been boring.
Control: Like most other borers, these insects thrive on stressed trees. Healthy, well fertilized trees are less susceptible to borers. Mulch trees to prevent mower injury and moderate soil temperatures and moisture. Apply a residual insecticide in mid-May to kill beetles attempting to enter or leave remaining trees. Soil applied systemic insecticides (imidacloprid and dinotefuran) have been shown to reduce injury from this pest.
Fig 71. Bronze Birch Borer Bumpy Bark
Fig 72. Bronze Birch Borer Pealed
Order and Family: Coleoptera: Buprestidae
Host Plants: Most deciduous trees. Notably maple, flowering fruit trees, poplar and linden.
Damage and Diagnosis: Flatheaded apple tree borer is a common problem for trees subject to the stress of transplanting. Infested trees can be killed outright by the girdling grubs, or be snapped in half during a wind storm after the late stage weakens branches by feeding in the heartwood of limbs. Beetles will often attack south sides of the trunk causing splits and cracks (fig 73). Mature white, larvae are up to 1″ long. Adults emerging from “D” shaped exit holes are 1/2″ long and metallic. Mature white, larvae are up to 1″ long.
Biology: Wintering as a pupae or late stage larvae, most adults emerge in May and fly through summer. Adult females lay single eggs on the bark surface in cracks and crevices that hatch into larvae that bore through the bark to feed on the vascular tissue beneath. Later stage grubs bore into the heartwood and weaken limbs. Just prior to pupation, the larvae bores toward the center of the trunk to pupate. Adults take 1 to 3 years to complete their life cycle.
Control: Minimize plant stress during the first three years after transplanting. Apply a preventative bark spray (pyrethroid) to the trunk in May and wrap the trees to prevent frost cracking. Although neonicotinoid applications to the soil can reduce problems with this pest, precautions must be taken to protect pollinators that visit flowering trees.
Fig 73. Splits and ooze caused by flat headed borer
7. Root Feeders
Pests in this category feed on plant tissue below the surface. Although few insects fall into this category those that do can cause significant damage. The black vine weevil is common in the Midwest and a good example of an insect whose primary damage occurs underground.
Host Plants: Many trees and shrubs, especially, Yews, azaleas, rhododendrons, English ivy, euonymus and many perennials.
Damage and Diagnosis: Adults chew distinctive notches into the margins of leaves (fig. 74, 75). Note, that these notches are distinct from those caused by leaf cutter bees. Legless grubs feed on roots, and can girdle the plant in the spring by feeding on the root crown.
Biology: Early and late stage grubs winter in soil and resume feeding in spring. In early June adults begin to emerge from the soil and continue to emerge for several weeks. After 2 or 3 weeks of feeding, adults begin to lay eggs on the soil surface. Adults lay up to 500 eggs over the course of a month. They winter in all but the egg stage.
Control: Foliar applications of pyrethoids or acephate applied in mid July will kill beetles before they lay the bulk of their eggs. Soil drenches of a systemic neonicotinoid insecticide (imidacloprid) in June will kill adults and later grubs before they feed on roots, but be aware of pollinator protection on flowering plants. Applications of chlorantraniliprole (Acelepryn) in late August will kill grubs. Entomophagous nematodes can readily kill pupae and larvae in the soil. Nematodes must be kept moist for them to be effective. Applying them at night and irrigating is necessary. Since the nematodes are not effective against eggs, apply them during the spring and fall when larvae and pupae are present. Effective strains of Steinernema carposcapsae are commercially available.
Regulatory Issue: Nursery stock containing leaf notching weevils cannot be sold. Several products that contain a mixture of a pyrethroid and a neonicotinoid (eg Discus) can be applied to plants to remedy the situation.
Related Pests: Several other closely related root weevils (e.g. strawberry root weevil) cause very similar injury to trees and shrubs. Control methods are similar.
Fig 74. Black Vine Weevil damage
Fig 75. Black Vine Weevil
8. Agents of Disease Transmission and Rapid Decline
Many insects move between plants and pass on disease. A good example of this is fire blight, a bacterial disease that rapidly kills branches of plants in the rose family. It is passed on by bees as they move between flowers in tree. Because there are many good reasons not to kill bees, this disease is managed by planting resistant varieties of plants, pruning and in some cases applications of antibiotics. Sucking insects, like some aphids, leafhoppers, and whiteflies, or rasping insects like western flower thrips pass on diseases that cause tremendous problems for greenhouse growers and vegetable producers. Boring insects that pass on disease are a serious concern in the landscape, because they thrive on diseased and declining trees. When these insects spread the disease to healthy trees, those trees decline and provide more high quality food for these insects. This increases the number of insects feeding on diseased trees that can spread even more disease to healthy trees. Managing these insects requires breaking the cycle of positive feedback between the insect and the disease. The relation between Dutch elm disease and elm bark beetles provides a good example of the how this cycle can be broken. Similar disease insect relationships encountered in the landscape are as follows:| Insect | Host | Disease |
| Pine sawyer beetle Monochamous spp. | Scotch Pine | Pine wilt (nematode) Bursaphelenchus xylophilus |
| Sap beetles Nitidulidae | Oak | Oak wilt (fungus) Ceratocystus fagacearum |
| Engraver beetles Ips spp. | Pine | Blue stain fungus |
Smaller European elm bark beetle – Scolytis multistriatus (Marsham)
Native elm bark beetle – Hylurgopinus rufipes (Eichoff)
Banded elm bark beetle – Scolytus schevyrewi (Semenov)
Host Plants: Elms
Damage and Diagnosis: These bark beetles are important because they carry and spread Dutch elm disease, a lethal disease of American Elm. Beetles infested with this fungus pass on the disease when they feed on the twigs and shoots in the canopy of elm trees. Infested branches have twigs with yellow leaves (fig.76). The disease spreads rapidly down the branch, eventually killing the tree.
Biology: Breeding in the trunks and limbs of dead and dying elms, this beetle winters as a late instar larvae beneath the bark. In the spring, adults are attracted to the scent of recently pruned trees. They fly to the shoots of healthy elms and feed on the crotches of twigs and young bark. Dutch elm disease is spread to these limbs by adults carrying spores of Ceratocystus ulmi from diseased logs. When there is an epidemic of Dutch elm disease, most of the beetles are breeding in diseased wood and carrying the spores. After feeding on shoots adults fly to a dying elm to mate and breed in a limb or trunk. After the first beetles come to the breeding site, beetles of either sex emit a scent that attracts large groups of beetles to attack the tree. This mass attack helps to weaken the tree and makes it more suitable to the bark beetle grubs. These attractive scents are common among species of bark beetles and are called aggregation pheromones.
The smaller European elm bark beetle (SEEBB) has two generations a year and the native elm bark beetle (NEB) has only one generation a year. Banded elm bark beetle (BEBB) may have up to 3 generations a year. All three species of insects are found in Indiana.
Control: Management of these pests are most effective when elms in a community are managed in a coordinated plan that includes inspecting for trees with yellowing branches, and dead and dying trees. Beetles are controlled by managing the places where they breed. Trees recently killed or dying (>30% yellowed canopy) from Dutch Elm disease must be removed and destroyed by chipping or burning prior to April 15. This kills beetles developing in breeding logs before they fly to spread the disease.
Systemic insecticide injections are not likely to reduce the spread of the disease because the beetles must chew into the twigs or bark to reach the part of the tree that has the insecticide. In the process, infested beetles can transmit disease. Good sanitation, particularly the quick removal of dead limbs or dying trees is much more effective than insecticidal applications. To prevent spread of the disease by beetles, avoid routine pruning during the summer months. Healthy elms that are pruned during the flight season attract both species of bark beetles.
Fig 76. Dutch Elm Disease
Walnut twig beetle – Pityophtorus juglandi
Pathogenic fungus – Geosmithia morbidi
Damage: The most obvious symptoms of this disease are rapid wilting and browning of leaves on a central limb, with wilted foliage clinging to the dead branches (fig 77). Symptoms tend to develop with the onset of summer stresses. Beetle exit holes are extremely tiny and difficult to see. Small, dark stained cankers lie just under the bark and may be visible when a thin layer of bark is removed (fig 78). The bark does not slough off the trunks of walnuts killed by TCD, and mortality may occur in groups. Conclusive diagnosis of TCD requires laboratory testing. Trees are likely infested for up to ten years before showing initial symptoms, but once symptoms appear, decline and death are rapid (usually within 3-4 years).
Biology: The flying adult walnut twig beetle carries a canker-causing fungus from infected to healthy trees. Large groups of adult beetles attack stressed trees. These beetles dig tunnels just beneath the bark surface where they mate and reproduce. Each beetle attack produces a separate darkly stained fungal canker. The fungus cuts off the tree’s circulatory system and the beetle feeds on the fungus. Eventually cankers grow together and cut off nutrient flow
Control: As of this writing, only the fungus has been reported in the state. If you suspect a walnut is suffering from TCD, please send a sample to the Purdue Plant and Pest Diagnostic Lab and Call 1-866-NO-EXOTIC. There are no known chemical controls for the beetle or fungus, and it remains unclear if walnuts can be effectively protected from the fungus carrying beetle with systemic insecticides.
Fig 77. Thousand Cankers Disease dying trees
Fig 78. Thousand Cankers Disease, multi cank bark
Glossary of Terminology
- abdomen – The hind portion of the insect where digestion and reproduction take place.
- adult – An insect or mite with functional reproductive organs.
- aggregation pheromone – A pheromone that attracts insects and causes them to form large groupings. Used by bark beetles to promote mass attack. Multilure is a commercial formulation used for monitoring elm bark beetle activity.
- Bacillus thuringiensis – A bacterial disease that produces a poison which kills certain insects. Commercial formulations of this poison are available.
- boring – The act of drilling through plant tissue, especially stems, twigs, trunks, and roots.
- bronze – Brown discoloration resulting from many small light or tan spots caused by spider mite feeding.
- c-shaped scar – A pattern of feeding that results when some small weevils feed in the center of a leaf or on a fruit surface.
- caterpillar – A butterfly or moth larva.
- chewing – Refers to ability of insect mouth parts to chew food. Insects with chewing mouth parts can tear and crush food.
- circular scars – Feeding injury associated with leaf cutter bees.
- complete metamorphosis – The pattern of development from egg to adult where immatures are worm-like.
- conspicuous white wax – Waxy excretion that covers insects. A diagnostic feature of many insects.
- cornicles – Bumps on the hind end of an aphid.
- crawler – The immature nymph of a scale or a mealybug after egg hatch. It is the only stage of many scales that are able to walk.
- crochet – Hook like processes on the base of and insect proleg. Common on caterpillars.
- curl – A leaf or shoot distortion associated with lack of water or sucking injury.
- damage – Injury that is extensive enough to cause economic loss.
- diagnosis – The process of determining the identity of an insect.
- dieback – When limb and shoot extremities are killed leaving behind the dead limb or limb portion.
- elytra – The hardened forewing of a beetle.
- eriophyoid mites – A group of three closely related mite families characterized by a cigar shaped body and 4 visible legs.
- exoskeleton – The hardened exterior shell of an insect that gives structural support to the insect body.
- flagging – The rapid yellowing or discoloration of a branch due lack of water caused by pest injury.
- frass – Insect excrement.
- gall – The swelling of plant tissue around an insect or mite feeding on the plant.
- gall making – The inducement of gall production by an insect or mite.
- girdler – Insects that sever a twig or leaf by feeding on the outside.
- grub – A beetle larva.
- head – The front part section of the insect responsible for ingesting food, seeing, and in part, tasting. Eyes and antennae are attached here.
- honeydew – The sugary liquid excrement of sucking insects.
- injury – Physical removal, discoloration or distortion of a plant part.
- instar – The stage of an insect between successive molts.
- larva – An immature insect with complete metamorphosis.
- leaf mining – The act of feeding between leaf surfaces.
- leaf scorch – Leaf browning associated with rapid water loss.
- maggot – A fly larva.
- metamorphosis – The series of changes an insect passes through in its growth from egg to adult.
- molt – The process of shedding the skin between developmental stages.
- necrotic – Often used to describe brown leaf spots caused by insects that kill leaf tissue as they feed on a leaf.
- notches – Areas on a leaf edge where leaf tissue has been removed. A characteristic of feeding by some weevil adults.
- nymph – An immature insect with incomplete metamorphosis.
- oviposition – The act of depositing an egg.
- ovipositors – Specialized structures on the abdomen of an adult female that is used for depositing eggs. Some ovipositors responsible for gluing eggs to plant are relatively inconspicuous. Other ovipositors responsible for drilling into wood, or cutting into leaf tissues are more obvious. Ovipositors, as in the case of adult sawflies, can be good diagnostic characteristics.
- pheromone – A chemical secreted by an organisms for the purpose of communication with other individuals of the same species.
- photosynthesis – The process of capturing of light with chlorophyll pigment and using its energy to convert carbon dioxide and water into sugar.
- positive feedback – When one event is stimulates a second event that in turn stimulates the first event ( e.g. Dutch Elm Disease and elm bark beetles).
- prolegs – Fleshy, unsegmented legs on the body of an immature insect used for walking. Number and position of as well as presence of crochets are used to distinguish between sawflies and caterpillars.
- pronotum – A distinctive piece exoskelton that lies between the head and the attachment of first pair of wings on the first segment of the thorax.
- pruner – Insects that sever a twig or leaf by feeding from the inside.
- pupa – The intermediate stage between a larva and an adult with complete metamorphosis. Does not feed.
- residual toxicity – The amount of time after insecticide application when the material is toxic to insects.
- serpentine – Snake like form used to describe leaf mines.
- sex pheromone – A pheromone released by a female that is carried down wind to attract males. Commercially available formulations are used to trap and time insect activity.
- simple metamorphosis – The pattern of development from egg to adult where young superficially resemble adults with the exception of the size of wings.
- skeletonization – When insects remove tissue between leaf veins.
- sooty mold – One of several species of fungi with black fruiting bodies that grows on the sugary liquid excrement of sucking insects. In the family Capnodiaceace.
- stipple – White flecks on green leaves caused when chlorophyll is removed by a sucking insect. Common for lacebugs.
- sucking – Refer to the ability of insect mouth parts to remove food from a plant or insect by piercing tissue and ingesting food as if through a straw.
- tar spot – Black spots of plant bug excrement found on leaf undersides.
- test – The waxy shell produced by an armored scale. Made of wax and waste products.
- thorax – The middle part of the insect responsible for locomotion. Wings and legs are attached here.
- true leg – A jointed appendage attached to the insect thorax that is used for walking.
- vascular system – The circulatory system of a plants. Consists of xylem and phloem that conducts water and nutrients.
- web – Structure formed from silk excretion of insects.
- witches’ brooms – Cluster of stunted twigs. Associated with some forms of injury such as that caused by the honeysuckle witches broom aphid.
- yellow – A leaf discoloration that occurs when the green chlorophyll pigment degrades. Associated with sucking insect injury, or leaf aging.
- (True/False) Insects have four pairs of true legs.
- (True/False) One cultural control strategy to reduce the number of plants damaged by insects is to use a wide variety of plants in your landscape design.
- (True/False) Insecticides that are toxic to bees have a label that includes a warning that prohibits product use where bees are actively foraging. (applicable only to those that are toxic to bees)
- (True/False) Because there are many good reasons not to kill bees and because it is passed by bees from flower to flower, fireblight (a bacterial disease afflicting members of the rose family) is managed by planting resistant varieties of plants, pruning and in some cases applications of antibiotics, but not the use of insecticides.
- What insect damage category includes insects that consume entire leaves or leaf parts?
- Leaf miners
- Gall makers
- Borers
- Honeydew producers
- Defoliators
- Predatory insects is an example of which category of tactics used to prevent damage to plants from insects?
- cultural
- mechanical
- biological
- chemical
- Which type of insects are insecticidal soaps useful in controlling?
- sucking insects
- immature insects that must still undergo several molts
- soft bodied insects
- Mimosa Webworm, Bagworm, and Eastern Tent Caterpillar are examples of which category of caterpillars?
- Concealed
- Diurnal
- Abysmal
- Exposed
- Which of these are examples of how insects injure woody plants?
- Chewing
- Skeletonizing
- Sucking
- Ovipositing
- All of the above.
- (True/False) Applying pesticides only when enough pests are present to threaten the appearance of a plant is environmentally superior to spraying by the calendar, because pests are not always present in the landscape.
- False
- True
- True
- True
- E
- C
- C
- A
- E
- True