Emerald Ash Borer
Agrilus planipennis
A metallic-green wood-boring beetle from Asia whose larvae tunnel beneath the bark of ash trees, cutting off the flow of water and nutrients and killing nearly every untreated ash within a few years of infestation. It is one of the most destructive forest and landscape pests in North America and has killed tens of millions of ash trees.
🔎 How to spot it
The adult is a slender beetle about three eighths to five eighths of an inch long with bright, shiny metallic-green wing covers and a coppery-red abdomen visible under the wings. The larva is a creamy-white, legless grub up to about an inch long with a flattened body made of bell-shaped segments. In practice the tree itself shows the clearest signs, described below.
🥀 Damage it causes
Larvae feed in winding, S-shaped tunnels packed with frass just under the bark, scoring the wood and girdling the tree. The classic signs are thinning and dieback that start at the top of the canopy, sprouts along the trunk, vertical splits in the bark, D-shaped exit holes about an eighth of an inch wide, and heavy woodpecker activity stripping the bark to reach the grubs. Most untreated trees die within two to four years.
🛡️ Prevent it
Do not move firewood, which is the main way the beetle is carried to new areas. Keep ash trees healthy and watch for early canopy thinning, especially once emerald ash borer has been found within fifteen to thirty miles. A high-value ash can be protected with preventive systemic insecticide treatments, but these must begin before serious decline and be repeated for the life of the tree.
🧯 If it is already here
There is no cure for a heavily infested tree; once a tree has lost more than a quarter to half its canopy it usually cannot be saved and should be removed before the brittle dead wood becomes a hazard. Trees still in good condition can be kept alive with trunk-injected or soil-applied systemic insecticides applied by a professional on a regular schedule. Replacing lost ash with a diversity of other species is the long-term answer.
💡 Good to know
Because the beetle kills almost all untreated ash, communities generally decide tree by tree whether to treat the best specimens or remove and replace them. Early detection matters enormously, since treatment only works while the canopy is still mostly intact. Quarantines and firewood rules exist specifically to slow its spread.
For educational and informational purposes only. Pest control advice is general guidance drawn from university cooperative extension sources; always identify a pest positively and read and follow the label on any product before use, especially around food crops, children, and pets.