Pest description, crop damage and life history
Pest monitoring Once the crop emerges, watch for wilting, lighter green or purpled plants, or reduced growth that may indicate a maggot infestation. Pull up affected plants, and check roots and soil to confirm the presence of maggots. If several rows of seedling plants are infested, plants may be removed and rows replanted. Drenching with insecticide is also an option, but such treatments are difficult, costly, and may not be adequate. If roots are tunneled but no maggots are present, maggots have left the roots to pupate, and insecticide treatments would be of little value. Sticky traps, bucket traps, and sweep nets also can be used to monitor the adult fly.
Rove beetles prey on eggs and young maggots. Rove larvae parasitize the pupa stage of the maggot. The parasitic wasp Trybliographa rapae lays its eggs in the maggot larvae if the larvae are close enough to the soil surface. Biological controls cannot be counted on to provide adequate control.
Where maggots are a perennial problem, grow seedlings for transplants in fumigated soil in the greenhouse or under frames of clear plastic. Avoid hardening transplants near infested fields. Direct-seeded crops may avoid some injury if a set of drag chains, attached behind the planter, eliminates the moisture gradient in the seed row. It is believed that adult flies can locate the seed row for egglaying by homing in on the higher moisture levels created when the soil is overturned for planting. Cover crops with floating row covers or screen cages prior to emergence of adult flies to prevent egg-laying. Do not put row covers in areas previously infested.
Older plants may outgrow moderate cabbage maggot populations if maintained with a careful irrigation schedule. Always disc under crop residues immediately after harvest. Maggots can survive for some time in crop residue. Do not follow susceptible crops with susceptible crops, unless sufficient time has passed for the residue to dry or decompose completely.
Management-chemical control: HOME USE
- azadirachtin (as a mix with pyrethrins)-Some formulations are OMRI-listed for organic use.
- pyrethrins-Some formulations are OMRI-listed for organic use.
Management-chemical control: COMMERCIAL USE
- cyantraniliprole (Verimark) at 0.088 to 0.176 lb ai/A at planting only, as in in-furrow spray or transplant drench. PHI 1 day. REI 4 hr. Do not exceed 0.176 lb ai/A at planting. Do not exceed 0.4 lb ai/A per season.
- diazinon (Diazinon 50W) at 2 to 3 lb ai/A. Broadcast before planting. REI 4 days. Rutabagas only.