Arborcare-Arborscape, Inc. 2018
Birch Leaf Miners
Birch leaf miners are small, black sawflies that attack some species of birches including river, water, and European white birches. Infection from birch leaf miners can be first detected by grayish areas on the leaf surrounding the eggs. Adults emerge around May and lay eggs in slits in the leaf surface. These hatch within 1-2 weeks and the larvae burrow into the leaf forming greenish blotches. The larvae feed between the upper and lower surfaces of the leaf (called mining), beginning at the midrib and continuing outward. The eaten areas die quickly, turning brown. If enough of the tissue is mined out of the leaf it may eventually kill the entire leaf.
Birch leaf miners produce 3-4 generations per year. After the eggs hatch, the larvae feed for about 8-13 days. They then travel down to the soil where they form cocoons and pupate. Adults emerge in about 17 days. The fourth generation normally does not develop during the current year. Instead, the larvae travel to the soil to overwinter in their cocoons. This generation will mature the following spring.
Unfortunately there are no cultural controls that will help control birch leaf miners. There are a few natural predators, however, that could give some control. There are also some chemicals that will help. Systemic chemicals give better control than contact materials as the larvae are under the leaf’s surface. One thing to note is that birch leaf miners will not kill your tree. If the infestation is bad enough, however, it can weaken the tree and make it more susceptible to other insects and diseases, as well as make the tree unattractive from the visible leaf damage.
We offer both soil systemic and foliar applications for birch leaf miners. The soil treatment is done in the early spring and will control the leaf miners all season. If sprays are needed we recommend 2 foliar applications. The first spray is done in the late spring when the adults are emerging, with the second following a few weeks later.
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