Insects feed on all parts of trees — roots, leaves, transport system, heartwood; each can be damaging in their own way. Keeping a handle on the most damaging of these is a key component of providing good tree care for your clients. A little research and a lot of effective communication goes a long way toward delivering a quality insect control program that does the job for the trees, puts money in your pocket and makes your customers happy.

Outcomes, results, consequences

Why focus attention on leaf feeders? In short, these critters are plant food-maker removers. They chew, extract and sponge up the very material that’s needed by trees to keep them vigorous and healthy. If not controlled, they’ll slowly cause a decline in a tree that, over time, can weaken it to the point that it may not recover.

The good news is that in most cases, an otherwise healthy tree can withstand one year’s worth of defoliation and still recover. Two years of defoliation… maybe, but maybe not. Beyond that, it gets pretty dicey.

How does this occur? Because leaves are the primary creator of necessary plant nutrition, removal of or damage to them brings about a need for the use of stored carbohydrates in the stems and branches to produce a new set of leaves. If the feeding occurs in spring, the usual result is the growth of new leaves to replace the ones lost earlier. If the damage is in summer or fall, the result is a prevention of the food that would have been made if the leaves had remained on the tree for the full season.

Another reason to focus attention on leaf feeders: they’re visual to the customer. Clients may not be able to see borer damage or stem girdling roots in the early stages, but they’ll surely see beetles and sawflies.

Scouting and monitoring

Perhaps the best place to start with managing leaf feeders is with scouting. Most arborists in the field know what the desired tree is supposed to look like, whether it’s a linden, crabapple, oak, hickory, spruce, Kentucky coffeetree, larch, pine, birch or persimmon. When a tree appears slightly different than what you’re used to seeing, a red flag should be raised. Keep in mind that this could be due to an actual disease, insect damage or any number of abiotic causes. For example, the culprit could be compacted soils, deep planting, overwatering, root damage from trenching, previous topping procedures, inadequate infiltration of water on a slope or a nutrient deficiency.

To get a good handle on the initial symptoms of tree insect problems, it’s wise to consult one of the many available references. For fear of leaving some of them out, the authors suggest typing “leaf-feeding insects on trees” into your favorite search engine (Yahoo Image Search, MSN Images and Google Images are examples).

Several good textbooks and mobile device apps are also available. It’s best to start with the ones in your state — or at least your region — as some insects can appear differently from place to place. The sources that include color pictures of early and fullblown signs and symptoms tend to be the most helpful.

Observation of the initial symptoms of a leaf feeders’ presence is of key importance to keeping them in check. When noticed early in the life cycle, before feeding damage is heavy, several options for control may be available. In some situations, the lower recommended rate of a control product can be utilized rather than the higher end of the range, which saves on money for materials as well as puts less insecticide or miticide into the environment and increases the chances for success.

Scouting involves observing differences in a tree’s appearance. You can also investigate by taking a closer look using a hand lens. Factors to consider include recent cultural practices, weather events that took place in the area recently and making comparisons from a tree species one location in the neighborhood to another.

The overall process of inspection is called monitoring, which essentially is a series of individual scouting events. Monitoring usually involves consulting customer records to look for notes on outbreaks of insect and mite problems, their extent, when they occurred and any control measures that were taken.

In terms of scouting frequency, at a minimum, it’s helpful to monitor before and after a pesticide application to confirm the presence of the feeder as well as to determine the effectiveness of the control attempt. Depending on weather conditions and product used, more frequent inspections can be necessary.

Treatment Methods

With relation to leaf feeders, each of the four treatment methods have positives and negatives:

Trunk injection

Pros: Direct product movement into the transport system of the tree and reduced potential for off target site movement of the active ingredients via slopes and drift.

Cons: Tree wounding and time for treatment depending on product choice.

Soil drench

Pros: Direct uptake, especially appropriate for smaller trees.

Cons: Potential for movement to water sources and damage to pets/children.

Basal spray

Pros: Translaminar movement into the xylem, good for smaller trees.

Cons: Certain products aren’t appropriate for this treatment method; drift may be consequential in some landscapes.

Foliar spray

Pros: Direct contact with pests in vulnerable life stage.

Cons: High potential for drift when wind speeds are greater than 5 to 8 mph.

Selling the program

In order to accomplish the true goals of scouting and monitoring, it’s necessary to sell a program of some type to your customers. After all, waiting for a call from a client to complain that their tree has been damaged allows for tree damage by its very nature. Again, this may be satisfactory for healthy, vigorous trees, but for those that are struggling or have a common number of flaws, it runs short of ideal.

A more proactive approach is to presell a bi-weekly or monthly or seasonally timed inspection program. What do you want to include in the program? Start with the following:

  • Documentation of the species;
  • Condition of the tree;
  • Any observed pests;
  • Previous pest damage evidence;
  • Previous treatments of property’s trees

These programs are commonly referred to as plant health care programs, which are designed to keep the tree healthy and provide for its needs, whatever they may be — soil improvements, pest control, fertilization, pruning, traffic avoidance, replacement, short-term cabling or bracing and tree risk assessment.

A key difference between the two approaches is that the react style of tree care usually involves getting paid for the volume of product that can be sprayed or injected into a tree. The plant health care option hangs its hat on obtaining compensation for an arborist’s training, experience and knowledge, as well as the control measures.

Some classic leaf feeders include:

An elm leaf beetle.

Image Courtesy Of James Kalisch, UNL

Elm leaf beetles

  • They feed on the foliage of European, American and Siberian elms.
  • As an adult, they measure about 0.25 inches long and are yellowish-green with a black stripe on the outside of each wing cover.
  • Larvae reach about 0.375 inches in length and are yellow with black spots and stripes.
  • Overwinters as an adult, hiding in and around buildings or in leaf litter and bark crevices. As new spring foliage begins to expand, these overwintered adults will emerge and begin feeding. After this they mate and lay clusters of yellow eggs on the undersides of leaves.
  • The eggs usually hatch in springs and the emerging larvae will feed and go through three larval stages of growth. The larval stage feeds by skeletonizing the underside of the leaf surface, creating a window pane effect at first and then a lacy leaf later. After feeding for a few weeks, the larvae pupate on the tree trunk and emerge as adults.
  • Adult beetles may also feed on leaves, leaving behind characteristic shot-hole type damage. Heavily infested trees often prematurely lose their leaves.

Spring cankerworm larvae.

Cankerworms and other caterpillars

  • They feed on most species of deciduous trees and some shrubs, but elm and hackberry are their favorites.
  • There are both spring and fall cankerworms and the difference lies in how they spend the winter. Fall cankerworms emerge as adults in fall (October typically), mate and lay eggs that overwinter. Spring cankerworms overwinter in the soil as a pupae and emerge as adults in the spring. Both species’ eggs hatch in the spring and cause damage at the same time of year.
  • It can be hard to tell the species apart, as both are grayish-brown and about 0.312 inches long. Females are wingless while males have greyish-brown wings, with an average wingspan of 1.125 inches.
  • Wingless adults emerge in the spring, when they mate and climb a nearby tree to deposit eggs under flakes of bark on the trunk and branches.
  • The larvae also look very similar, about 1 inch in length and yellowgreen to brownish to blackish.
  • You can distinguish the two species by counting the number of prolegs on the back half of the abdomen; fall cankerworms have three pairs, spring cankerworms only two.
  • Upon hatching, the caterpillars or “measuring worms” feed voraciously on the leaves, at times completely stripping the tree. Severe defoliation over a few consecutive years may weaken, but is unlikely to kill, the tree.
  • After feeding, larvae enter the soil near infested trees to overwinter. There’s only one generation per year.

Spider mites in various life stages

Aphids

  • These occur on almost all species of woody ornamentals. They feed predominately on the undersides of leaves, but also are found on the tender shoots of plants.
  • Most are green, but they can vary in color from pink to black.
  • Aphids have needle-like mouthparts that help them to feed on plant sap. As they feed, they cause plant leaves to curl and their defecation is known as honeydew, a sticky liquid that can coat leaves, branches and even objects under the tree. Honeydew can also serve as a breeding ground for black sooty mold.
  • The best time to control aphids is early in their life cycle, for three reasons. First, smaller aphids succumb to treatments more readily than older and larger ones. For greatest effectiveness, insecticidal sprays should be directed toward the undersides of the leaves.
  • There are several options for aphid control, ranging from organic products like neem, insecticidal soaps, horticultural oils and synthetic insecticides such as permethrin, lambda-cyhalothrin or cyfluthrin.
  • Because aphids have a relatively short life cycle and can regenerate quickly, multiple treatments may be necessary for acceptable control.

Spider mites

  • Although not technically an insect, (insects have six legs and three body parts, while adult mites have eight legs and two body parts) they’re the prototypical sap suckers.
  • Under cool and moist springtime conditions, Spruce spider mites multiply rapidly on conifers such as spruce, juniper and others. Damage isn’t usually noticed until the weather becomes hot and dry later in the summer. As the summer progresses, two-spotted spider mites can become a problem on essentially all landscape ornamentals.
  • Mites can be detected in two ways: First, use a 10-times hand lens to look for moving critters on the underside of a broadleaf tree leaf or on the new growth of a conifer. The body and legs of motionless mites should be clearly visible, while moving mites in motion may simply appear as moving dots. Second, place a white sheet of notebook paper under a branch or group of leaves and rap them with a small stick. If mites are present, they’ll fall onto the paper where they can be easily seen.
  • If one or two mites are found on a leaf, immediate treatment is usually not necessary. But continue to monitor the tree for any changes in the mite population. If more than six to 10 mites appear on the sheet of paper, consider a treatment with a miticide such as bifenthrin (Talstar).
  • While sap-sucking insects may have a common method of feeding, keep in mind that each should be considered individually when it comes to selecting the most appropriate control strategies.

An adult Japanese beetle.

Japanese beetles

  • These are invasive scarab beetles that, as adults, feed on over 400 different kinds of plants. Preferred hosts include lindens, birches, roses and grapes.
  • They’re found in most of the Eastern and Midwestern states.
  • Adults have sharp, chewing mouthparts that skeletonize leaves, eating the green tissue and leaving behind only the veins of the leaf, shred flowers and can hollow out fruit.
  • Control of adults that feed on trees begins before you see the first beetle. Most adults emerge between June and August — if a tree is to be preventatively protected, a systemic application of imidacloprid should be applied to the soil at the base of the tree in April or May to allow the tree to absorb the treatment. (You can’t treat linden trees with any neonicotinoid insecticide.)
  • If you’re treating for already-present adults, bifenthrin, carbaryl and cyfluthrin all provide two to four weeks of residual protection. Chlorantraniliprole also offers four weeks of protection, with minimal effects on nontarget organisms such as pollinators.
  • Organic products like neem and pyola protect leaves and need to be reapplied every three to seven days, depending on the weather and pest pressure.

Bagworm.

Bagworms

  • These are common pests of evergreens, junipers and occasionally deciduous trees and shrubs.
  • The case or bag that provides a home for the bagworm caterpillar — which gives the insect its name — is constructed of silk and fragments of leaves or needles.
  • Bagworms overwinter as eggs within the bags. In the spring, during the first or second week of June, tiny larvae hatch from eggs and immediately begin construction of small protective bags.
  • Caterpillars feed from within their bags and move along the branch in search of food. Applying Bt in June, when the larvae are small, is the best control strategy.