Tree Insects & Diseases

Plant pathology is the scientific study of diseases in plants. The interaction between trees and insects is varied. These range from symbiotic relationships, like pollination, to diseases that can kill trees. A number of insects infect trees and, acting as parasites, cause disease in them. The diseases may cause hindered growth, defoliation or even mortality in some cases.

Asian Longhorned Beetles

The Asian longhorned beetle, or ALB, was first found in Brooklyn, New York, in 1996, the University of Minnesota states. Adult beetles are tree insects that lay eggs in an opening they find in the bark. The larvae then bore large grooves deep into the wood. These grooves, which are actually created for feeding, interfere with the vascular transfer of nutrition in the plant. This makes the tree so weak that it practically falls to pieces and is dead within a short span of time. Trees favored by the Asian longhorned beetle are predominantly maple trees, although horse chestnuts, willows and elms are also possible targets. ALB is considered an extremely dangerous insect, as there is no known way to prevent or control this disease. An infected tree is generally cut down to arrest the spread of these beetles.

Eastern Tent Caterpillar

Cherry trees may be affected by the presence of the Eastern tent caterpillar. These tree insects lead to defoliation in early spring. Infestation is prevented by removing cylindrical egg masses around small twigs. Presence of these caterpillars may be detected by silk webs in branch crotches, or if the larvae are seen by the naked eye. The caterpillars strip extensive stands of trees of all leaves, leading to slow growth rate in the trees, apart from affecting limb and bud formation.

Elm Bark Beetle

The elm tree is affected by the presence of leaf beetles, which are tree pests. They are primarily responsible for the overland spread of Dutch elm disease (DED).This disease mainly affects urban trees. According to University of Minnesota, DED is a major problem for elms in the United States. DED can be transmitted to healthy trees in two ways: when bark beetles directly infest the tree or in cases of root grafting. This also leads to defoliation, sometimes at a very heavy rate in elm trees. The larvae that are born on the tree stunt its growth. The leaf beetles infect almost all kinds of elm trees.

Zimmerman Pine Moth

The presence of the Zimmerman pine moth may indicate disease in pine trees. Scotch, Ponderosa and Austrian pines are also susceptible. The Zimmerman pine moth, considered a tree pest, has a one-year life cycle. In this case, the affected parts break off from the points where they are attached to the main trunk. Generally when a tree is infected, dead and dying branches begin to appear in the upper half of the shoot. Infestation is detected by the appearance of popcorn-like pitch masses on the tree. These irregular growths may attain the size of golf balls, or may appear like a cluster of grapes. To prevent this disease, drenching trunk spray should be applied in August or mid-April to kill the larvae before they enter the tree trunk. Zimmerman pine moth can be controlled only when larvae are active, which is when they are exposed on the bark in spring and late summer.

Keywords: tree insects, tree pests, tree disease

About this Author

Based in Northern California, Devin Dupre-Neary has a bachelor's degree in nursing from UC Davis. Rather than move towards a master's or work in a hospital, he chose a different route. In 2009, he wrote professionally, part-time, writing articles on a host of subjects from health issues to gardening.