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Tree and Shrub Insects

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Types of Tree and Shrub Insects


Aphids are small soft-bodied insects that suck plant juices. High aphid populations can cause leaves to yellow, curl, or drop early. The most bothersome aspect of aphids is the honeydew they produce. Honeydew is sugary water excreted by aphids. Sooty mold grows on the honeydew creating a sticky, unsightly mess on trees, sidewalks, and automobiles.

CONTROL: Insecticide applications will help control aphid populations.


Bagworms are caterpillars that make distinctive spindle shaped bags on a variety of trees and shrubs. They attack both deciduous trees and evergreens, but are especially damaging to juniper, arborvitae, spruce, pine, and cedar. Large infestations of bagworms can strip plants of their foliage and eventually cause them to die. Bagworms pass the winter as eggs inside the bag that contained the previous year’s female. An insecticide application will be needed to prevent serious damage.


Most woody landscape plants can be attacked by borers. There are many types of borers, the Emerald Ash borer being the most known. The larvae bore beneath the bark into the wood on tree limbs, trunks, and main roots. Damage can vary from foliage being discolored, wilt, limbs may die back, and branches or entire plants may die. Borers attack mostly damaged or dying plants. Healthy trees are rarely attacked. Pesticide applications to the bark have not been found effective. Injections of insecticide can provide control depending on the damage that is already done. The best prevention is to keep trees healthy.

Carpenter Ants

Carpenter ants nest underground or in wood. They do not eat wood, but their tunnels weaken limbs causing them to decline. Carpenter ants feed on insects, honeydew, and plant sap. Keeping plants properly pruned, preventing injuries, and controlling the insects will help prevent carpenter ants and termites from attacking the trees.

Fall Webworms

Webworms also feed on deciduous trees. Their webs are formed over the foliage toward the outer portions of the tree. Adult moths emerge in the late spring or early summer and are mostly white. In June or July, the females lay eggs beneath leaves. These eggs hatch in about 10 days and feed in the silken tents until late summer or early fall. The use of a high-pressure insecticide spray will penetrate the webbed foliage and control the worms.

Insect Gall

In the spring, before leaves are fully developed, insects lay eggs in the leaf or stem of a variety of plants. Galls are abnormal growths of plant cells that a formed around these eggs. After a brief period of cell growth, the gall stops developing. The insect becomes enclosed by the gall and feeds only on gall tissue during its development. Small holes on the outside of the gall indicate that the adult insects have emerged. Generally galls do not seriously harm the plant. If your tree or plant is already unhealthy or under stress, the damage that does occurs can be to a greater extent than that of a healthy plant. Keeping trees and shrubs fertilized, irrigated, and pruned properly will help keep plants healthy.

After the formation of galls it is impossible to eliminate the insects with insecticides because they are enclosed and protected inside the gall. Galls that occur on the leaves will drop off with the leaves but those on the trunk or stems may persist for several years. Controlling galls with insecticides is usually not practical because there is minimal timing to control the adult pest before the gall is formed.

Lace Bugs

Most adult lace bugs are about 1/8 inch long and flat. The body is concealed beneath lacelike forewings. The nymphs and adults live on the lower surface of the leaves and suck juices through slender, piercing mouth parts. This produces yellow or whitish spots on the upper surface of the leaf. Applications of insecticide to the lower leaf surfaces will limit their infestation.

Leaf Hoppers

There are several hundred species of leafhoppers. Most adult leafhoppers are ¼ inch or shorter. Some species are bright colored while others blend in with their surroundings. Leafhoppers suck the juice from various plants causing the leaves to appear stripped, pale, or brown. The best control is to have the landscape sprayed with the dormant oil to reduce any overwintering eggs.

Leaf Miners

The larvae of several different families of small moths are the most common foliage-mining pests in the landscape. These leaf miners feed inside the leaves, needles, shoots, or buds. Leaf miners cause off-color patches, trailing patterns, or holes in leaves. Severe infestations can slow plant growth, but established plants are rarely killed by these insects. Pruning out and disposing infested foliage along with insecticide applications will help keep these insects under control.


Scale insects feed by sucking plant juices, and some may inject toxic saliva into plants. Most scale species are one of two types, armored or soft. Armored scale is less than 1/8 inch long and has a plate like shell. Soft scale are 1/4 inch or smaller. Scale are also honeydew excreters. Soft scale have several annual generations which overlap so that multiple life stages are usually present at once. High infestations can kill a plant rather rapidly.


Spider mites suck fluid out of the plants cells killing tiny areas of leaf tissue. This causes leaves to appear flecked with pale dots. They also cover leaves, shoots, or flowers with large amounts of fine webbing. Heavy infestations can slow plant growth, cause leaves or fruit to drop prematurely. Applications of miticides will help control spider mite infestations.

Tent Caterpillars

Tent Caterpillars feed on deciduous trees throughout the U.S. Adults are hairy, medium-sized moths, usually dull brown, yellow, or gray in color. Tent caterpillars overwinter in eggs that are gray to brown in color. The eggs laid encircle small twigs or a flat mass on bark. The larvae hatch and begin feeding on the leaves. The silken webs are formed around the juncture of branches. Pruning out the infected branches and the use of high-pressure insecticide sprays will help with the control.

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