As a general rule, the most damaging tree insects are the ones that bore into the sapwood. Borers cause significant interruption in the conductive vessels of the tree, the plant world’s equivalent to ripping veins and arteries out of a person’s arm. On the other hand, that’s not a good reason to ignore the leaf feeders. In fact, these chewers can do quite a bit of damage, especially if they go unnoticed for a year or two before the customer brings you into the picture.

Regular inspection

Regular inspection is crucial for many reasons, one of which is the need to identify current problems before they turn into major outbreaks. While leaf feeders are normally considered less damaging, they can be nearly invisible, especially on taller trees where they are not easily observed by clients. While unusual patterns or occurrences such as sawdust and holes in the bark caused by borers are fairly noticeable, leaf feeder damage can be hidden in the foliage. Leaves serve a very important function for trees — they photosynthesize, producing sugars and carbohydrates essential for the overall health of the tree. If leaves are lost due to insect-induced defoliation, this critical function is greatly diminished. To prevent injury from leaf loss, implement regular inspection regimes for your customers or the properties you manage. Don’t do it for free.

Foliage inspection on a regular basis is critical. Photo: John Fech

Foliage inspection on a regular basis is critical. Photo: John Fech

There are several forms of invoicing for services rendered in today’s business world. Whichever you choose, make sure to charge your clients a reasonable rate for your inspection and diagnostic services. As a professional arborist, your years of experience and training have a certain value and your clients should recognize this. Charging for diagnosis and regular inspection is a great way to distinguish yourself and your business from the “mow, blow and go” outfits, many of which were in another line of work last year. The cost should be based on several factors including the region of the country you provide services in, the level of training and experience you have, and the competition from other arborists.


Aphids occur on nearly 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 their color can vary from bright red to yellow to black. Aphids possess piercing-sucking mouthparts that they use to withdraw plant sap.

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, larger ones. Second, as aphid colonies develop leaves often curl around the aphids, protecting them from predators and shielding them from insecticide applications. Finally, aphids excrete a sticky substance called honeydew that collects on lower leaves and branches and creates fertile growing areas for sooty mold. The end result is not only unsightly, but also reduces the photosynthetic surface of the tree leaves.

For maximum effectiveness, insecticidal sprays should be directed toward the underside of leaves. Because aphids have a relatively short life cycle and can rapidly recolonize an area, multiple treatments may be necessary for acceptable control.

 European pine sawfly larvae Photo: John Fech

European pine sawfly larvae Photo: John Fech

Leafhoppers and treehoppers

Leafhoppers are easily identified by their characteristic wing pattern, size, shape and color. About 1/5 to .25 inch in length, leafhoppers hold their wings at a sharp angle, similar to a small camping tent. They often match the color of the plant tissue upon which they are feeding, most commonly green, yellow or gray. Treehoppers often have extraordinary pronotum patterns that can resemble spines, horns or keels. Some species are thorn-like in appearance.

Unlike many of the other sap-sucking insects, leafhoppers are reasonably good fliers and easily move from tree to tree to escape predators and arborists. These insects inhabit most broadleaf trees, but seem to prefer honey locust, ash and oak.

Because of their ability to fly, insecticidal soaps and horticultural oils are not always effective. Residual insecticides, including the synthetic pyrethroids, as well as systemic treatments are preferred. Fortunately, damage from leafhoppers is usually not severe enough to require treatment.

Spider mites

Although not technically insects, (insects have six legs and three body parts, while adult mites have eight legs and two body parts) spider mites are the quintessential sap suckers. Under cool, moist springtime conditions, spruce spider mites can rapidly multiply on conifers including spruce, juniper and others. Damage is not usually noticed until the weather turns 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 10x 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 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 sharply with a small stick. If mites are present, they will fall onto the paper where they can be seen easily.

If one or two mites are found on a leaf, immediate treatment is usually not necessary. However, 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.

Twomarked treehoppers Photo courtesy of James Kalisch, UNL.

Twomarked treehoppers Photo courtesy of James Kalisch, UNL.


Sawfly larvae resemble caterpillars, but are actually the immatures of primitive stingless wasps. Sawflies feed on a wide variety of evergreens and broadleaf trees, and therefore are quite variable as a group in terms of their behavior, feeding habits and life cycles.

Pine sawfly larvae vary in color from grayish to yellowish green. Some species of pine sawflies have one or more lengthwise stripes. Larvae typically reach .75 to 1 inch in length and rear up in a characteristic defensive “S” shape when disturbed. Most species overwinter as pupae in the soil beneath trees, but a few spend the winter as eggs inserted in the needles. In the spring, sawfly larvae feed in clusters on needles, starting at the needle tip. Feeding habits among species vary, but those that feed only on old or young needles weaken trees or slow their growth, while species that feed on both young and old needles may kill or cause severe injury to trees. After feeding for several weeks, the larvae of most species drop to the ground, spin cocoons and pupate in the soil.

Cankerworms feed on most species of deciduous trees and some shrubs, but elm and hackberry are their favorites. Spring cankerworms overwinter in the soil. Wingless adults emerge in the spring, mate, and then climb a nearby tree to deposit eggs under flakes of bark on the trunk and branches. Adults may emerge as early as late February and early March during warm periods. Upon hatching, the caterpillars, or “measuring worms,” feed voraciously on the leaves, at times completely stripping the tree. Severe defoliation over a number of consecutive years may weaken but is unlikely to kill the tree. After feeding is completed, larvae enter the soil near infested trees to overwinter. There is only one generation per year.

Spring cankerworm. Photo courtesy of James Kalisch, UNL.

Spring cankerworm. Photo courtesy of James Kalisch, UNL.

Leaf miners

Leaf miners can be deceiving from a diagnosis standpoint in that the larval stages feed on the inside of the leaf, mainly parenchyma tissues, before obvious symptoms are visible on the outside. A good example is the hawthorn leaf miner, which causes damage in early summer. Leaf miner feeding disrupts important physiological function of the leaf, and blighting causes a significant reduction in the aesthetic value of the tree visually. Leaf miners can be controlled through properly timed foliar treatments as well as trunk injection.

Controlling leaf feeders

Applying a foliar insecticide to mature, fully grown leaf feeders can be problematic on two fronts: First, lack of effectiveness. Large insects are generally more resistant to insecticide applications than newly hatched ones. Second, the opportunity to prevent damage has been lost. Chances are they’ve already done most of their feeding for the year and an insecticide application does little more than provide revenge for the property owner. Applying residual insecticides such as the synthetic pyrethroids (e.g., bifenthrin, cyfluthrin, cypermethrin, deltamethrin, lambda-cyhalothrin and permethrin) or systemic treatments (chlorantraniliprole, clothianidin, Di-Syston, imidacloprid and thiamethoxam) while infestations are just beginning to develop and insects are still small is a much better option.

Injections also offer the potential for “rescue” treatments. However, because of the potential for injury to the tree cambium, it’s best to consider this option only when spray applications would cause injury to surrounding elements such as cars, buildings and other personal property items.