Individual cone-shaped screen covers, made from standard window screen fixed to a wooden frame, can be useful in the home garden. They are easily constructed and can be used year after year. Covers can be removed when plants grow big enough to tolerate damage.
A barrier that can be used to protect transplants, but is not as effective as the screen cone, is a 3-inch-diameter disk of tarred paper, foam rubber, or other sturdy material placed flat around the base of each plant as it is transplanted. Each disk has a hole in the center for the stem to go through. The disk will prevent flies from laying eggs near the plant stems and may provide places for the aggregation of predatory ground beetles that eat the maggot's eggs and larvae.
Be sure transplants are maggot-free before planting them. Once maggots are infesting a crop, there is no reliable way to control them.
