Leaf miners are the larvae of several insects, including moths, beetles and flies. They hatch on leaves, then bore inside the epidermal layers and begin to feed on the tissue inside, forming tunnels. Often classified by the mine patterns they create, leaf miners can be described as serpentine, blotch or tentiform. The aspen leaf miner is one of the most prosperous leaf miners, with more than 659,000 acres of Alaskan forest being infested with them in 2006.
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Leaves that are host to leaf miners will dry out, die and drop from the tree. In most cases this is a superficial problem that, while appearing unattractive, does not affect the tree's overall health. Leaf miner damage resembles the effects of abiotic leaf problems, although the latter will cause the leaves to collapse inside with no hollow areas.
The yield of mature trees has not been shown to be affected by leaf miner infestation. Younger trees and saplings, however, may suffer poorer fruit harvests as more frequent leaf flushes make them more susceptible to severe infestation. Leaf miners can inhibit photosynthesis by up to 75 percent, reducing growth and preventing the tree from setting as much fruit.
Although the main effect that leaf miners have on a tree is cosmetic, a severe infestation can cause greater damage. The reduction in photosynthetic ability due to defoliation can result in branch dieback and stunted growth. Infected trees may also be more vulnerable to other insects and disease.
Severe damage caused by leaf miners is rare, as they have natural enemies that keep their population in check. Watch for signs of infestation such as leaf curling and silver-colored tunnels on leaves. Outbreaks do not last long, but they can be treated with parasitic wasps, persistent contact insecticides or systemic neonicotinoid insecticides. Promote good health in your trees by watering, pruning and fertilizing appropriately to avoid pests.