Spinach leafminer

The spinach leafminer attacks spinach, beet, sugar beet, perpetual spinach and many weeds including lamb's-quarters, chickweed and nightshade. The insect's mines make the vegetables unsightly and unappetizing as well as destroying part of the crop.

Symptoms
The maggots feed between the upper and lower leaf surfaces of the host plants mining out the tissue in between. As the maggot grows, the mines coalesce with others and blotches are seen on the affected leaves.

Crop rotation
Because this insect overwinters as a puparium in the soil near where the crop was infested the previous year, crop rotation should be practiced especially if one tries to mechanically protect plants from this insect.

Netting
Cover plants with fine netting or cheesecloth or floating row covers to protect them from adult egg-laying flies. Netting will not keep out insects that are already in the soil. Be sure that the edges of the row cover are well anchored so insects cannot get under them. The protective covering should be placed over the crop at planting time and, with spinach, might be left on until ready to harvest.

Culling
Hand pick and destroy infested mined leaves when first seen before the larvae drop to the soil will help control the leafminers. If leaves are just placed on a compost pile, fly larvae might continue to develop and emerge as adults to reinfest crops.