The emerald ash borer (Agrilus planipennis, EAB) is a non-native forest pest known for its bright green color, devastating impacts on the environment, and massive economic cost.It was first officially detected near Detroit Michigan in 2002, though dying ash trees were observed as early as the late 1990s. Since then, federal and state agencies, non-profit groups, and a variety of other organizations have worked to stop the spread of this beetle. However, these efforts have been mostly unsuccessful, and the beetle continues to destroy ash trees throughout eastern North America. EAB was found in South Carolina in August 2017, and as of 2021, is present in Pickens, Oconee, Anderson, Greenville, Spartanburg, and York counties.
EAB is a type of jewel beetle (Family Buprestidae). Adults are bright metallic green, reminiscent of an emerald. Its abdomen can be purple or a reddish-brown, and its antennae, located below two giant eyes, are segmented in a way that makes them look serrated. The larvae are white or cream colored, with a body that is segmented into trapezoidal shapes. The larva’s bulbous head is slightly darker in color than the rest of the body, which is flattened. Both adults and larvae are relatively small, with adults about 0.3 to 0.5 inches long and the larvae about 1.0 to 1.3 inches in length.
EAB will attack and infest any species of ash (Fraxinus) tree. Common species of ash trees in South Carolina are green (Fraxinus pennsylvanica) and white (Fraxinus americana), with Carolina (Fraxinus caroliniana) and pumpkin (Fraxinus profunda) being less common. EAB has also infested white fringetree (Chionanthus virginicus), though this is uncommon.
The EAB life cycle in South Carolina takes one year, though it can last two years in more northern areas. Eggs are laid in bark crevices. After about 10 days, eggs hatch and larvae chew their way into the tree, where they feed on the phloem underneath the bark. Larvae go through five life stages, or instars, inside the tree. As the larvae eat, they create winding galleries in the phloem, and these galleries get wider as the larvae grow. Larvae construct chambers just inside the outer bark of the tree to pupate and emerge after one to two weeks. Adults chew their way out of the bark, creating a characteristic D-shaped hole. Adults feed on the foliage of the host tree, and mating begins after the meal.
Signs of Damage
There are several telltale signs of EAB damage on an ash tree. While adult feeding damage on foliage is very difficult to detect, the D-shaped exit holes made when adults leave the tree are much easier to see. Larval feeding creates vertical cracks in the bark, beneath which you can often see the winding larval galleries. Woodpeckers are a predator of the larvae and often increase in number if a tree is infested with EAB, and their feeding often results in strips of outer bark being flaked off. This causes the bark to appear lighter in color (this is known as “blonding”). Epicormic sprouts growing at the bottom of the ash tree are another indicator of EAB. These sprouts are a sign the tree is very stressed and an indicator that the tree likely doesn’t have long to live.
Economic and Ecological Importance
EAB has caused disastrous effects on our nation’s natural resources and economy, and costs associated with EAB are estimated at about $134 million dollars annually. Ash trees are commonly planted in urban and residential areas for their ornamental and street tree value. They are used for lumber and other wood products, including baseball bats, and ash is commonly used as a windbreak tree. The ash tree population in South Carolina is valued at around two million dollars, and the major cost associated with EAB is mostly tree removal, which is expensive and time consuming. Ash is a critical component of some riparian areas, and species that depend on ash as a resource are threatened as EAB eliminates ash across much of eastern North America.
Management in Natural Areas
There are two primary ways to combat the spread and destruction caused by EAB. Biological control is the use of other organisms, usually other insects or fungi, to control unwanted pests. Several species of tiny parasitic wasps are being used that attack EAB eggs and larvae, preventing them from becoming adult beetles. Biocontrol is never 100% effective but can provide some measure of EAB population control in areas otherwise difficult to reach. Removing the host trees is also an option, particularly if a landowner wants to obtain some value from their ash trees before they are killed.
Management in Urban and Residential Areas
Several insecticides are available and effective for controlling EAB on high-value trees or trees in urban or residential landscapes. Ideally, one should start applying insecticide treatment before the tree is infested. Once these treatments are initiated (usually applied yearly or every other year, depending on the specific treatment), they will likely be necessary for the remainder of the tree’s life. Insecticides (including dinotefuran, emamectin benzoate, azadirachtin, and imidacloprid) can be applied in different ways, including as a soil drench (applied at the base of the tree), trunk spray, or trunk injection. Affordability, environmental impact, and effectiveness of the application are all factors in deciding a treatment type. These treatments should be done by a licensed pesticide applicator. Remember, with all pesticides, the label is the law, and these chemicals must be applied in the manner that is specified on the label. Heavily infested trees likely cannot be saved and will need to be removed by a licensed professional.
Preventing the spread of EAB
While EAB can spread on its own (it can fly several miles at a time), one of the most common ways woodboring insects (including EAB) move is by humans – especially in firewood. If you are traveling more than a few miles, it is best to purchase or obtain your firewood locally. Moving firewood long distances can unknowingly spread wood-inhabiting insects and fungi.
- The National USDA APHIS EAB program homepage: https://www.aphis.usda.gov/aphis/ourfocus/planthealth/plant-pest-and-disease-programs/pests-and-diseases/emerald-ash-borer
- The Emerald Ash Borer Information Network: http://www.emeraldashborer.info/
- The South Carolina Forestry Commission Insects and Disease homepage: https://www.state.sc.us/forest/id.htm
- The Don’t Move Firewood homepage: https://www.dontmovefirewood.org/
- The Southern Regional Extension Forestry Forest Health and Invasive Species Program: http://southernforesthealth.net/insects/emerald-ash-borer