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. Various types of leafminers attack a wide-range of trees and plants, including, birch, boxwood, cypress, magnolia, oak, and many other types of trees. In order to live and eat within the small confines of a leaf, most leafminers are small flatworm-like insects. As the leafminer feeds on the interior of the leaf, the leaves become blistered and blotchy, and the outlines of tunnels can often be seen. As the infestations increases, the leaves yellow, brown, and die. Often, as the leafminers mature, they begin to consumer larger and larger parts of the leaf.
The most effective way to control leafminers is to apply Once-A-Year Insecticidal Drench w/Merit early in spring. This will provide protection against leafminors and most other insects during the full growing season, and will kill the juvenile miners inside the leaves.
Since leafminers are protected inside the leaf for most of their lives, sprays have only limited effectiveness. Borer-Miner Killer can be applied as soon as the juveniles or adults emerge from the leaves. The effectiveness of the Borer Miner Killer Spray is increased when it is used with Nature's Own Spray Helper, which helps increase the degree of penetration into the leaf.