Leaf Miners
Pest · Commonly affects: Spinach, Swiss chard, Beets, Tomatoes, Peppers, Lettuce
Leaf miners are the larvae of several insects, most commonly small flies in the family Agromyzidae, though some moths, sawflies, and beetles also mine leaves. They matter to gardeners because the larvae feed hidden inside leaf tissue, where they are protected from contact controls and can quickly disfigure leafy crops and ornamentals.
How to identify it
Look for winding, pale or tan serpentine tunnels, or irregular blotchy patches, that appear just under the leaf surface and often widen as they go. Holding a leaf up to the light may reveal the tiny larva or dark specks of frass inside the mine. The adults are small dark or yellow-marked flies, and you may notice rows of light stippling on leaves where females punctured the tissue to lay eggs or feed.
Damage
The larvae eat the green tissue between the upper and lower leaf surfaces, destroying chlorophyll and reducing the leaf's ability to photosynthesize. Light mining is mostly cosmetic, but heavy infestations can brown and collapse leaves, stunt young plants, and make leafy greens like spinach and chard unmarketable or unappetizing.
Prevention
Rotate leafy and susceptible crops to a new bed each year so overwintering pupae in the soil do not emerge into a fresh planting, and clean up and remove crop debris at the end of the season. Give plants adequate spacing and keep them vigorous with healthy, well-drained soil and steady watering, since strong plants tolerate light mining better. Time plantings to avoid peak adult flights when possible, and control nearby weeds such as lambsquarters and nightshades that host the same leaf miners.
How to manage it
Pinch off and destroy individual mined leaves as soon as you spot them to kill the larva inside before it matures and drops to pupate. Cover susceptible crops with floating row covers right after planting so egg-laying adults cannot reach the leaves, using this only on crops that do not need insect pollination. Encourage and protect natural enemies, especially tiny parasitic wasps that attack the larvae inside the mines, by keeping flowering plants nearby and avoiding broad-spectrum sprays, and set out yellow sticky traps to monitor adult flies.
General guidance for US home gardens, focused on prevention and non-chemical control. For a confirmed diagnosis and options specific to your area, contact your local Cooperative Extension office. Page updated Aug 4, 2026.