Turnip (roots and tops) and rutabaga-Cabbage maggot

Delia brassicae

Pest description, crop damage and life history

See:

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.

Management-biological control

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.

Management-cultural 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 (neem extract)-Some formulations are OMRI-listed for organic use.
  • pyrethrins-Some formulations are OMRI-listed for organic use.
  • zeta-cypermethrin

Management-chemical control: COMMERCIAL USE

  • chlorpyrifos (Lorsban Advanced) at 0.05 to 0.1 lb ai/1,000 row ft or 2.11 lb ai/a soil surface spray. PHI 30 days. REI 24 hr. Band and incorporate to 1 inch at planting, or side-dress immediately after transplanting. Use at least 40 gal/a spray. Do not exceed 2.25 lb ai/a per year. Apply only once per season.
  • diazinon (Diazinon 50W) at 2 to 3 lb ai/a. Broadcast before planting. REI 4 days. Rutabagas only.