Pest description, crop damage and life history
Pest monitoring Once the crop emerges, watch for wilting, lighter green 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 and sweep nets also can be used to monitor the adult fly.
Rove beetles prey on maggot eggs and young larvae. 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 when a set of drag chains is attached behind the planter to eliminate the moisture gradient in the seedrow. It is believed that adult flies can locate the seed row for egglaying by honing in on the higher moisture levels created when the soil is overturned for planting.
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
- pyrethrins (often as a mix with other ingredients)-Some formulations are OMRI-listed for organic use.
Management-chemical control: COMMERCIAL USE
- Chenopodium ambrosioides extract (Requiem 25EC) at 4 to 6 pints formulated product per acre, soil application. REI 4 hr. OMRI-listed for organic use.
- chlorpyrifos (Lorsban 15G) at 0.03 lb ai/1,000 row ft. REI 24 hr. Apply as an in-furrow drench at planting with at least 40 gal/a total spray. Do not exceed 2.75 lb ai/a or one application per season.