Choose selective pesticides for treating other pests, if possible, to avoid this problem. Other parasites attack leafminers, but the leafminer feeding habit protects them from most predators. Where possible, avoid planting next to infested fields, especially those near harvest. Regularly check young seedlings for leafmines. Most mines occur on cotyledons and the first true leaves.
Some mines are most obvious from the underside of the leaf.
If leafminer populations build to high levels when seedlings have 4 to 5 leaves, a chemical treatment may be necessary. Treat if you find more than an average of one mine per leaf in your overall field sample. To be effective, sprays must be applied to the larval stage. For use on head lettuce only. Is effective at killing larvae in the mines.