BIRCH LEAFMINER AND
BIRCH BORER

Birch leafminer is a very common pest of all birch species in the urban landscape.  In Calgary, it is particularly common in neighborhoods of the deep southeast, such as Mackenzie Towne, Cranston, and Mahogony, but the problem is city-wide.

Leafminers are tiny sawflies, jet-black, wasp-like insects. They overwinter as larvae in the soil and pupate in the spring. Adults mate and begin egg-laying, in the leaves, in mid-late May. The caterpillars feed on the inside of the leaf tissue, leaving the characteristic skeletonized, brown, patchy leaf. There are several different species of birch leafminer and a potential for several generations per year.

While leafminers generally do not kill the tree, they weaken it, leaving it stressed and open to attack by other insects, notably the bronze birch borer, a much more serious pest that ultimately kills the tree, usually over the course of several years.

Control is either by direct trunk injection or by systemic spraying, in mid to late May. Early June treatments can also be effective.  Annual treatment is necessary to provide the best control.