Aphids are small, fuzzy, white, green, winged or wingless insects. These insects can cause discolored foliage throughout a tree or shrub. On conifers, needles may turn yellow or red in summer and drop in fall. On deciduous trees, leaves appear stippled. Many aphids secrete large amounts of honeydew (partly digested sweet and sticky plant juices,) which causes foliage to glisten and results in abundant bee and ant populations.

Aphids have mouth-parts that pierce and then suck the sap from foliage and plant stems, which stresses trees and shrubs due to a depletion of plant nutrients. Honeydew droplets on cars, decks, and walkways can be dangerous and troublesome as the sap causes surfaces to be slippery.

Adult Black Vine Weevils leave C-shaped notches in leaves when they feed, however it is difficult to spot adults as they hide in ground litter and tend to become active at night. Leaves and whole branches of affected plants may become yellow.

The grub (or larva) stage is very destructive as it feeds on plant roots, which causes overall decline or death of the tree or shrub.

These borers leave D-shaped exit holes in the trunks and limbs of trees they have infested. Their flat, irregular, winding galleries beneath the bark of the main trunk are sometimes visible. Chlorotic leaves and sparse foliage are early symptoms of borer presence (particularly in the upper crown). As the infestation increases, symptoms include complete branch or trunk dieback.

Injury is caused by larval feeding galleries that girdle the trunk or branch, resulting in trunk or branch dieback.

At maturity, this caterpillar is about 2" long, black with white lines down its back, and has yellow hairs. The pest creates white, silken nests in branch crotches and can cause defoliation.

When caterpillar populations are large, trees become covered with webbing and the majority of their leaves are devoured. This damage can be displeasing and can potentially lead to tree death.

Symptoms of EAB are similar to the Bronze Birch Borer. New, vigorous sprouts form at the base and/or along the limbs of infested trees, and crown dieback is typical. D-shaped exit holes show up where the borer emerges and heavy woodpecker activity results in limbs that look stripped.

Larvae feed on the inner bark and phloem, creating winding galleries as they feed. This tunneling cuts off the flow of water and nutrients in the tree and ultimately leads to dieback and death.

When fully grown, this caterpillar is around 2" long with a yellow body and either a black or red head. Symptoms of this pest include small, white, silken nests out on the tips of branches and overall defoliation in those areas.

The insect is detrimental to the beauty of its host but is more a nuisance than a threat to the overall health of the tree.

Adult beetles are 3/8" long with a metallic green-bronze exterior. They often feed in groups causing the skeletonization of leaves. At a distance, infested trees can have a scorched, lacy appearance.

Adult beetles feed on leaves; larvae feed on the roots of grasses. Trees that consistently lose their leaves may have their energy reserves deplete, which can reduce their ability to withstand other potentially harmful pests.

Leaf miners cause unsightly, light-green to brown blotches or serpentine mines in the leaves of infested plants. Heavy feeding can cause the entire leaf to die, and a heavy infestation can damage a tree or shrub. Affected areas can eventually die, which results in irregular holes in the canopy.

Injury caused by leaf miners spoils the appearance of ornamental trees and reduces the tree's vigor and growth.

Sawflies look like small caterpillars but are actually more closely related to wasps and bees. Damage results in sparse or missing needles or foliage anywhere on the tree or shrub. Conifer needles sometimes look curly and straw-like.

Insects cut or saw into plant tissue when laying eggs. Minor infestation on larger trees is usually not problematic, but damage caused on smaller trees and shrubs can be significant and result in complete defoliation.

Insects assemble in large numbers and attack leaves, stems, flowers, and twigs and produce lots of honeydew. Honeydew then promotes the growth of sooty mold fungi, which turns the affected area black.

This insect sucks the phloem sap out of the infected tree. Injury appears as foliar discoloration, deformation, wilt, and eventual death of affected plant parts caused by loss of sap.

Mites are microscopic spiders. Their feeding results in stippled, grayish-green foliage. When large spider mite populations are present, large portions of the leaves or needles can turn blotchy or pale-yellow. Some mites produce fine webbing over the surface of the infested foliage.

The mouthparts of this pest penetrate leaf or needle cells and extract the sap, destroying the chlorophyll-containing cells and causing stress to infested plants.

Adelgid galls are found mainly on new shoots and/or at dense needle clusters. Galls appear to be ¾ to 1" long and are green or brown and pineapple-shaped. Infested shoots become brown, stunted, and deformed.

The galls cause the infected shoots to grow improperly, resulting in occasional twig death.

Trees infested with white pine weevils typically present a dead or dying terminal leader. Occasionally, the top whorl of branches will die as well. When infested, the terminal leader will have the look of a shepherd's hook.

The larvae feed on the inner bark and the sapwood of the top portions of susceptible trees. This damage can be aesthetically unpleasing and detrimental to the development of proper form.

Larvae are white, reddish-yellow, or green and approximately ¾" long. The adult moth is reddish gray in color and has wingspan of 1 to 1 ½". Symptoms of this pest include pitch masses located at branch whorls on the trunk and a discolored or broken leader directly above the coagulated pitch mass.

Feeding may result in a dead lateral limb or main leader and can cause stress to infested trees.

Signs can vary between hosts, ranging from leaf spots and blights of leaves and shoots to cankers and dieback of twigs and branches.

In severe cases, infected leaves and leaflets may drop from the tree, causing defoliation and reducing the appearance and vigor of the host plant.

Olive-green spots appear on the leaves of trees infected with scab. Leaves may turn yellow and drop prematurely, and the fruits are disfigured. The disease is most severe when humidity is high and temperature is moderate in spring and summer.

Premature leaf drop is common for infected trees. Repeated defoliation stresses trees and leads to decline and poor flowering.

This canker shows up as yellow or orange-brown to black discolored areas on the bark of the trunk and branches of infected trees. On spruce trees, the disease has more of a gall-like appearance and black fruiting bodies may occur on the canker.

Cankers occurring on large branches, in the main crotches, or on the tree trunk enlarge, causing death of the affected part by cutting off the flow of nutrients and water.

The first visible symptom of this disease is usually the wilting and yellowing of leaves in the upper portions of the tree's crown. Branches die very quickly (4-6 weeks). Cross sections of infected wood reveal black staining in the cambium area of the sample.

Dutch Elm Disease eventually leads to the decline and death of infected trees.

Symptoms of needle cast usually first appear as light green and yellow spots and then turn orange or purple-red in color. This disease causes the needles to die and fall prematurely.

The damage caused by the disease varies between species. Early damage can reduce vigor and compromise aesthetics. If the tree remains untreated, needle loss can result in branch death, overall thinning of the foliage, and, in severe cases, death of the entire tree.

Symptoms of this disease vary between oak species. Leaves may curl, droop, or wilt when trees are infected. Noticeable brown streaks in the sapwood are another symptom of oak wilt.

Death in red oaks and decline in white oaks.

The tips of infected branches turn brown in early summer. A gray band will appear at the base of the affected branch or shoot. In some cases, the branch will develop a small canker, girdling the branch and causing dieback.

Progressive dieback until the entire branch is killed. On some occasions, an entire young tree can die from this disease.

The leaves and twigs of deciduous trees with this disease are covered with a grayish-white, dusty mildew.

Severe infections may cause leaves to turn yellow, dry up, and fall prematurely. The disease also can detract from the visual appearance of plants.

Early symptoms appear as pale spots on the upper surface of the leaf. As the disease progresses, the underside of leaves will contain brightly-colored blisters. These blisters break open to expose yellow, orange, or rusty brown spores. Galls also sometimes form depending on the host and strand of disease.

The damage caused depends on the type of host, but most rusts detract from the appearance of foliage and reduce the host’s vigor. Severe infections cause leaves or needles to fall prematurely in mid-summer.

Tar Spots show up on maples in late spring to mid-summer. These spots start off as light green in color and then turn black during mid to late summer.

Leaves with multiple black spots will sometimes fall prematurely, but this disease rarely causes trees much trouble. Tar spot is one of the most noticeable yet least damaging of the foliar diseases.

Tip blight results in the stunting of new growth and browning of infected needles. The disease often starts in the lower branches of trees, but branches throughout the tree can be affected on a particularly wet spring.

This disease causes the slow decline and eventual death of needles as new growth continues to be infected by older growth.

A sudden wilting of the leaves on one limb, multiple limbs, or even the entire tree. These symptoms vary per tree. Dark sapwood discoloration may be noticeable from pruning cuts, but vary between tree species.

These fungi invade the xylem and cause death or disfigurement of plants. Damage caused includes curling, drying, or abnormal red or yellow color of the leaves or areas between leaf veins, as well as defoliation, wilting, dieback, and death.