Description
Leafminers are insect larvae that feed inside a leaf, between the upper and lower surfaces. They may be the larvae of flies, moths, sawflies, or beetles. Females lay their eggs on or in the leaves, and the larvae that hatch from these eggs burrow into the leaves. Leafminers must be able to survive in a small living space, so they are tiny and somewhat flattened. The thinner the leaf the flatter and smaller the leafminer. As the larvae mine the leaf tissue, there is more room for them to expand, but their heads always remain somewhat flattened. Leafminer feeding produces blisters, blotches, or tunnels in the leaf, which turns yellow or brown as the tissue dies. If more than one larva is mining the tissue, the tunnels often run together, forming large blotches that cover much of the leaf. Infested plants may have a scorched appearance. Many adult leafminers continue to feed on leaves, using their ovipositop to puncture the leaf and suck up the plant sap.
Control
Leafminers are protected inside leaves for most of their lives, which makes control difficult. If the spray used for control is not a systemic insecticide, then sprays must be applied when the adults emerge to lay their eggs. Most ornamentals can be sprayed with the systemic insecticides acephate or disulfoton. Food crops can also be treated with an insecticide containing diazinon or carbaryl if the spray is carefully timed. Check with your local County Extension Agent (see County Extension Agents) for the best time to spray for the insect in your area. Make sure your plant is listed on the spray label.
