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, consuming partial or whole areas inside the leaves. Larvae can sometimes be seen easily when leaves are held up to the light. The entire lifecycle, from adult leaf miner to egg, larvae, and pupae, takes from 6-8 weeks. Homeowners don't often see the damage until the insect is gone and may think the birch leaf has dried up because of heat or has a disease.
Birch Leaf miner damage is usually superficial and aesthetic so natural controls generally supply sufficient 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 because they have not yet 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 read labels carefully, especially since Birch trees have some sensitivity to the use of insecticides. Note that there is no relationship between Birch Leaf miner damage and bronze birch borer attacks.
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Updated Wednesday, October 12, 2016