Use transplants. Older plants may outgrow moderate cabbage maggot populations if well irrigated. Cabbage maggots do not develop at temperatures below 43° F. Plant before or after peak adult maggot flight in the spring (300 degree days at base 43° F. after soils thaw). A floating row cover or cheesecloth tent, which has no gaps through which flies can enter, may be placed over the seed furrow or transplants at planting time. The tent base should extend at least 6 inches on each side of the stems. Standard "backdoor" screening constructed with scrap wood framing has also shown excellent results as a fly barrier in WSU experiments. Washington State University scientists tested other non-chemical techniques on experimental plots. Two popular treatments, use of garlic sprays or wood ashes, had little value.

Do not add uncomposted manure or plant residues, such as fresh grass clippings, to soils. Root maggot adults are attracted to raw organic matter to lay their eggs. There is some indication that well-composted materials may reduce maggot problems. Till under infested plants immediately after harvest. 

Numerous parasites and predators attack cabbage maggots, but usually do not reduce populations quickly enough to avoid damage in the short run. Among these parasites are the Rove beetle (Aleochara spp.), an 1/8 inch, black to reddish-brown beetle, and wasps in the Braconidae, Ichneumonidae, also the wasp, Trybiographa rapae. Among the predators are a number of the ground beetles.