Birch leafminer feeds in the leaves of most birches in Bucks and Montgomery County including river birch, paper birch, gray birch, and European white birch. Search for irregular blotches on the leaves throughout the canopy when looking for signs of this pest. Leaves may turn brown, paper-like, and eventually drop off. The entire tree can look scorched or blighted from a distance with foliage at the top turning brown first. The adult is a four winged black fly-like insect about 1/4” long. The larvae are flat, white, and 1/2” long at maturity and feed between the layers of the leaf. Mature larvae over-winter in debris in the soil. Adults emerge and mate as the leaves begin expansion in the spring. After mating, the female adults insert their eggs in soft, newly developing foliage. The eggs hatch 7-10 days later into larvae and feed for 2-3 weeks before dropping to the ground to enter the soil and pupate. A second generation of adults appears 15-20 days later to start the cycle over again. In our area we often see multiple generations per year.
Control of the birch miner may be provided by a soil or trunk injected insecticide. This can also protect the tree from the bronze birch borer, which causes additional stress by cutting off vascular flow of the tree. Foliar spray applications can be done, but repeated applications are necessary for proper efficacy. The size of the host, time of year and also proximity to water must be considered when choosing an appropriate treatment.
Contact Plant Health Solutions for proper diagnosis and to develop a treatment plan.