The Invasive Pest That's Attacking Trees In South Carolina

When you've visited a park or campground you may have noticed warnings telling you to only use firewood you've purchased at the site, or wood for sale that displays the seal of the Department of Agriculture Animal and Plant Health Inspection Service. This regulation is meant to help suppress the spread of invasive pests like the emerald ash borer (Agrilus planipennis), an insect first seen in South Carolina in 2017 that can travel via infected wood. These green beetles cause about $134 million in damage annually by killing landscaped trees and forests, affecting furniture and woodworking projects, and even destroying the timber used in baseball bats. Without the use of pesticides or biological control, it's almost certain the trees, once infested, will die. Even worse, it only takes three years for EABs to kill even the largest trees.

EABs almost exclusively attacks species of ash (Fraxinus spp.) such as the Carolina ash, white ash, and green ash. Luckily, Mountain ash (Sorbus americana) is not really an ash, and is therefore not susceptible to the insects. However, EABs also attack white fringetree (Chionanthus virginicus), but not to the extent they affect ash trees. In South Carolina, the life cycle of an EAB is one year. Eggs are laid in the bark, become larvae that eat the material under the bark, and eventually mature into beetles that chew their way out of the tree, causing significant damage during the process. Depending on the weather, the insects emerge in early spring to mid-summer.

Detecting the presence of EABs is very difficult before trees show signs of infection — though there are some ways to identify a diseased tree in your yard. The top of a tree may thin and then die back, and small branches may grow just below the dead part of the trunk, but trees with these symptoms have probably already been infected for a few years. The adult insects themselves are metallic green, hence the emerald name, and roughly half an inch long. If you pull back the bark of a tree that you think is infected, you'll likely see 1.25-inch-long, creamy larva if EABs are present. Other signs of infestation are D-shaped holes created when adult beetles emerge, channels burrowing into the layer of wood under the bark, or an unusual number of woodpeckers coming to the tree to feed on the larva.

Controlling EABs has been difficult in South Carolina, partly because of the ease of spread. Adult beetles can only fly a few miles, but don't mind hitching a ride with humans who unwittingly transport them in infected wood. In natural areas like forests, two methods are used to control the invasive pest: Tiny parasitic wasps that eat the eggs and larva are introduced to kill the beetles, or the trees that are infected are removed. A simpler solution is not to plant ash trees. River birch (Betula nigra), silver maple (Acer saccharinum), and hackberry (Celtis occidentalis) can be solid alternatives.