Spinach and Swiss chard leafminer flies are 1/2 inch long and gray with black bristles. This leaf miner lay eggs on the underside of the leaves side by side singly or in batches up to five. The damaged leaves are unmarketable. One larva may feed on more than one leaf. The larvae drop from the leaves after feeding for about two weeks onto the ground where it pupates and overwinters in the soil as pupae. In spring, they appear from mid April to May and they cause serious damage compared to the other generations that appear later. However, leafminer attack vegetables such as tomato, cucumber, and celery. Sometimes they also attack lettuce and parsley in the greenhouse but cause less damage to similar vegetables grown in the field.

Row covers, remove host weeds (chickweed, lambsquarter, nightshade), deep spring plowing or rototilling to bury overwintering pupae, remove attacked leaves, and apply insecticides (recommended in your state) on eggs before they hatch into larvae. Home gardeners should cut out the attacked area of leaf and use the rest of the leaf especially on Swiss chard.