Borers

Click on the thumbnail image for the larger photo.

Back to Insect Pests of Ornamental Plants

With their striking color patterns and exceptionally long antennae, long-horned beetles are a handsome lot. Their larvae are white, legless, and worm-like with somewhat swollen heads. Luckily, most species in this group infest only dead or dying trees. There are, however, a few important pests which will attack healthy trees and shrubs.

This is the adult locust borer, a serious pest of black locust.

Their larvae bore through the bark and tunnel extensively in the wood. Heavily infested trees may be so weakened that they break off in high winds.

The redheaded ash borer is a pest of ash, elm, hickory, oak, and linden. Females lay their eggs on weakened or newly transplanted trees. After hatching, the larvae feed in the inner bark and sapwood, sometimes completely cutting off the flow of sap.

Roundheaded borers attack twigs and small branches as well as the trunk.

Larvae of the dogwood twig borer tunnel down the center of dogwood twigs. Frequent holes to the outside allow them to expel their frass. Several other trees also serve as host for this insect, but the damage it causes is rarely noticed.

The second group of borers are the flatheaded wood borers. The adult beetles have hard shells with a metallic lustre. The heads of the larvae are expanded and flattened.

Like the roundheaded borers, these insects are found most commonly in unhealthy trees previously weakened by some other factor. This insect, the bronze birch borer, seeks out birch trees already in poor condition, then lays its eggs in bark crevices or near recent wounds.

Spiral swellings hide their winding feeding tunnels under the bark. Infested trees have sparse foliage and eventually suffer dieback in the upper crown.

Wood-chewing caterpillars make up the third and most important group of borers. When mature, these borers become clear-winged moths which often resemble wasps.

Early external symptoms of attack by the peach tree borer are a mass of gum and brown frass at the base of the trunk. A few strokes with an axe will expose the white caterpillars chewing away at the inner bark and sapwood. Peach, plum, and cherry are also attacked at the larger branch forks by a second moth borer, the lesser peach tree borer.

The dogwood borer is a close relative. All of these pests are difficult to control. Repeated applications of an insecticide with a long residual life will prevent additional egg laying by the adults, but borers already in the trees will not be affected.

Though the majority of wood chewing caterpillars belong to the clear-wing moth group, there are a few which are unrelated. The American plum borer, which attacks maple, sycamore, apple, peach, and other shade and fruit trees, is related to the meal moths which are pests of stored products.

A second example is the tulip poplar crown borer. No matter which group they come from, borers are dangerous pests. Once they are established, control is very difficult. Valuable trees and shrubs can be protected by keeping them in good, healthy condition and by taking prompt action if the symptoms of borer attack appear. When necessary, your local extension office can recommend an insecticide and the proper time to apply it.

Follow VCE

Social Media Directory

Contact Virginia Tech
Privacy
Acceptable Use

Virginia Cooperative Extension programs and employment are open to all, regardless of age, color, disability, gender, gender identity, gender expression, national origin, political affiliation, race, religion, sexual orientation, genetic information, veteran status, or any other basis protected by law. An equal opportunity/affirmative action employer. Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg, VA, United States; M. Ray McKinnie, Administrator, 1890 Extension Program, Virginia State University, Petersburg, VA, United States.