Leaf miners are small insect larvae that feed inside the leaves of the plant. Eventually the whole leaf may be destroyed. The damage done by these garden pests to our plants is easy to spot because of the “mines” created as the bugs chews inside the leaf. Most leaf miners are moths and flying insects that evolved and survived through this protection against predators.
In some instances the leafminer will cause a light colored blotch on the leaf, in really bad cases the plant will look discolored and/or drop leaves. It is rare that leafminers do enough damage to kill a plant, what they destroy mostly is the aesthetic value of your ornamentals for a short period of time.
Control: Most of the time there are enough natural predators, like parasitic wasps, that keep these pests under control. If you have to use an insecticide that is systematically carried throughout the plant. That means that you have to use an insecticide that is absorbed by the plant and carried to the leafs where it will come in contact with the larvae or be eaten by it.
Pick off infected leaves or spray with a pesticide as soon as the demage appears. Spraying may have to be repeated at fortnightly intervals in cases of bad infestation.
Leaf miner infection can be reduced or prevented by planting trap crops near the plants to be protected. For example, lambsquarter, columbine, and velvetleaf will distract leaf miners, drawing them to those plants and therefore reducing the incidence of attack on nearby crops.