The Emerald Ash Borer (EAB) is an invasive insect posing a significant threat to ash trees across North America. This small, metallic-green beetle, originating from Asia, has caused widespread devastation since its accidental introduction. Understanding EAB’s biology and impact is important for safeguarding ash tree populations, helping property owners and communities identify infestations and implement management strategies.
The Emerald Ash Borer: An Overview
The Emerald Ash Borer ( Agrilus planipennis) is a beetle native to northeastern Asia. Adult EAB beetles are metallic emerald green and typically measure around 0.33 to 0.5 inches long. While adults feed on ash leaves, causing minimal damage, the larval stage is responsible for the destruction.
Female EABs lay their eggs in bark crevices on ash trees. Upon hatching, the larvae burrow into the tree, feeding on the inner phloem, cambium, and outer xylem. This feeding creates long, winding, S-shaped galleries under the bark, which disrupt the tree’s vascular system. This disruption prevents the tree from transporting water and nutrients effectively, leading to the tree’s death, often within two to four years of infestation. The EAB life cycle can take one to two years, with larvae overwintering inside the tree before pupating and emerging as adults the following spring.
Identifying EAB Infestation
Recognizing EAB infestation signs is important. A primary indicator is the presence of D-shaped exit holes, approximately 1/8 inch in diameter, left by emerging adult beetles. Beneath the bark, infested trees exhibit characteristic S-shaped feeding galleries packed with a sawdust-like material called frass.
Other visual symptoms include vertical bark splitting, which occurs as the tree attempts to grow over the larval galleries. The tree’s canopy may also show signs of thinning and dieback, typically starting from the top. Stressed ash trees often produce epicormic sprouts, which are new shoots growing from the trunk or roots. An increase in woodpecker activity, often resulting in “blonding” of the bark where woodpeckers have stripped away outer layers, can also signal an infestation as they forage for larvae.
Strategies for EAB Management
Managing Emerald Ash Borer infestations includes preventative measures and treatment options. Maintaining tree vigor through proper watering, fertilization, and pruning helps ash trees resist pests. Preventing the movement of infested firewood is a significant preventative step, as EAB often spreads long distances through human transport of wood.
Chemical treatment options use systemic insecticides that the tree absorbs. These include soil drenches, trunk injections, and basal bark sprays. Systemic insecticides are effective and can protect trees for two to three years per application, typically administered by a licensed professional. Applications usually occur in mid-to-late spring or early summer to ensure the insecticide is present when larvae begin feeding. Biological control, involving the release of specific parasitoid wasps that prey on EAB eggs or larvae, is another long-term strategy to regulate EAB populations. If an infestation is severe, tree removal may be the most appropriate action to prevent further spread.
Post-Infestation Considerations
After an ash tree has been infested or removed, proper wood disposal is important to prevent further pest spread. Infested wood should be chipped or burned according to local regulations to destroy any remaining EAB larvae.
When selecting replacement trees, choose species not susceptible to EAB. Diversifying tree species in a landscape helps mitigate the impact of future pest outbreaks. Suitable alternatives to ash trees include various oak species, hackberry, silver maple, river birch, Kentucky coffeetree, lindens, and ginkgo. These contribute to ecosystem recovery and maintaining urban canopy.