Leafminers are the larvae of several species of flies, moths, beetles and sawflies. Adults lay eggs on or inside leaves, and after hatching the larvae burrow between the leaf surfaces, feeding as they travel. This creates the distinctive pale, twisting trails or larger blotchy mines visible from the outside. The larva is protected inside the leaf while feeding. Damage is usually cosmetic, but heavy infestations can reduce photosynthesis and weaken young plants.

How to Fix It
Remove mined leaves: Pick off badly affected leaves before the larvae mature and dispose of them.
Squish the larvae: On small infestations, follow the mine to the larva and crush it through the leaf.
Use insect netting: Fine insect netting can prevent adult insects from reaching susceptible plants to lay eggs.
Clean up debris: Remove infested leaves and crop residue where some species may pupate or overwinter.
Encourage beneficial insects: Tiny parasitic wasps are important natural enemies of many leafminers.
Avoid unnecessary insecticides: Broad-spectrum insecticides can kill leafminer parasitoids and sometimes make infestations worse.