Plant Problem Diagnostic
Leafminers: Identification and Control
The short answer
Leafminers are the larvae of certain flies, moths, or beetles that tunnel between the upper and lower surfaces of a leaf, leaving winding trails or blotchy patches. On vegetables the adults are often small yellow-and-black flies; hosts include leafy greens, beet, pea, tomato, onion, and squash. On ornamental plants and trees the damage is almost always aesthetic and rarely harms the plant.
Because natural enemies usually keep leafminers in check, control is often unnecessary. When you do want to act, start with physical and cultural steps: remove and destroy affected leaves while damage is small, control host weeds like lambsquarters, till after harvest to destroy pupae, and use fine-mesh row covers to keep egg-laying adults off vulnerable crops. If you are unsure whether action is warranted, your local Extension office can help you decide.
How to recognize leafminer damage
Look for pale, winding tunnels or irregular blotches inside the leaf, sometimes with a darker trail of frass. The insect lives inside the leaf tissue, so surface sprays are largely ineffective against the larvae.
- Winding trails or blotchy mines between the leaf surfaces
- Common vegetable hosts: leafy greens, beet, pea, tomato, onion, squash
- On ornamentals and trees, damage is usually cosmetic only
Cultural and physical control
- Remove and destroy infested leaves while damage is limited
- Control host weeds such as lambsquarters to reduce food sources
- Till the garden after harvest to destroy pupae in the soil
- Use fine-mesh floating row covers to exclude egg-laying adults
- Conserve natural enemies, which often control populations on their own
When control is not needed
On most ornamental plants and trees, leafminer damage is an appearance issue and does not require treatment. Even in vegetables, action is usually only warranted on leafy crops you eat directly, like spinach, when damage is heavy.
✔ If natural enemies are keeping numbers low, doing nothing is often the best choice; broad-spectrum sprays can kill those helpers.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- UMN Extension — Leafminers in home gardens — Leafminers often controlled by natural enemies; remove/destroy leaves, control weeds, till after harvest, use row covers; leafy greens hosts.
- University of Maryland Extension — Leafminers on Ornamental Plants — On ornamentals, leafminer damage is aesthetic and control is usually not necessary.
- University of Maryland Extension — Leafminers on Vegetables — Small yellow-and-black flies; vegetable host plants; management with row covers and removing infested leaves.