Bronze Birch Borer

Agrilus anxius

HOST Birch

DAMAGE/SYMPTOMS Girdling injuries cause dieback of limbs in the crown. D-shaped exit holes will be present on trunks and branches on parts of the tree that are unshaded. The infestations will also cause raised ridges in the bark. The galleries that are formed from boring underneath the bark make a zig-zag pattern and are packed with sawdust.

LIFE CYCLE Females lay eggs in bark crevices or in other protected sites. Egg laying begins in the upper crown of the tree or in branches (usually less than-half-inch thick) and then continues to thicker portions of the tree. The eggs will hatch after about two weeks. The larvae overwinter within the cambium and pupate in early spring. The adults exit the trees in late May or early June. There is one generation/year.

MANAGEMENT Birch are often stressed, making them more susceptible to the borer. Provide a large mulched area around the tree to conserve moisture and to protect the root system. Any limbs showing signs of infestation should be pruned out prior to beetle emergence in the spring. Preventive insecticides can be applied as trunk sprays (active ingredients include bifenthrin, permethrin, and carbaryl) and should be timed to coincide with egg laying in the summer. Systemic insecticides with the active ingredients imidacloprid, emamectin benzoate, azadirachtin, or dinotefuran can also be applied in the spring to prevent future infestations.

A Bronze birch borer adult. B Bronze birch borer damage on trunk.