Birch Leaf miner
Birch Leaf miners are small, black wasps (sawflies) that feed inside the leaves of many birch cultivars. Their feeding forms blotch type mines and partial or whole areasinside the leaves are consumed. Larvae can sometimes be seen easily when leaves are held up to the light. From adult leaf miner to egg, larvae, and pupae the entire lifecycle takes from 6-8 weeks. Homeowners don't often see the damage until the insect is gone and may think the birch has dried up because of heat or has a disease.
Despite their presence, Birch Leaf miner damage is usually superficial / aesthetic and natural controls play an important part in their management. Therefore there will not necessarily be damage the following year. If damage is extensive, the best time for control using insecticides is during egg hatch. The small larvae are the most susceptible stage for control as they have not entered deep into the leaf tissue where they are much less susceptible to the chemical. Systemic insecticides such as imidicloprid (Bayer Tree & Shrub Insect Control) would be the insecticide of choice during egg hatch. Always be careful to read labels especially since Birch trees have some sensitivity to the use of insecticides. It should be noted that there is no relationship between birch leaf miner damage and bronze birch borer attacks.
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Updated Tuesday, July 22, 2014