The SLM miner can cause extensive damage to crops in local areas. Beets, spinach, Swiss chard, and related plants and the weed, lamb's-quarters, are damaged by the larvae of this small fly, mining between the upper and the lower leaf surfaces. The maggots mine in a blotch fashion causing extensive damage to the leaves.
Infested leaves are unfit for food, and the plant's photosynthetic ability is impaired.
As much as 75 percent of the foliage can be destroyed by SLM maggots. The SLM adult is an inconspicuous, olive-gray fly. The adult flies come out in the spring and lay eggs on the leaves of the host plants. In 3 or 4 days, tiny maggots hatch from the eggs, burrow into the leaves, and begin mining. When fully grown, the maggot drops from the leaf, enters the soil, and forms a puparia out of its last larval skin.