To monitor field for eggs, check 20-40 plants in the field, in groups of 2-4 plants. If you find more than an average of 1 egg/stem, it is likely to be a damaging population (UMass Extension, 2009).
Management and cultural practices
- Plow-under crop residues immediately after harvest. Plowing destroys the pest and exposes pupae to ground predators and sunlight.
- Burn or destroy roots of crucifer plants when harvesting tops. Maggots can survive for some time in crop residues.
- Root maggots prefer to lay eggs in soil that is moist and with high organic matter. Do not plant susceptible crops unless the plant residues are dry and or completely decomposed.
- Planting clover (Trifolium spp.) as soil cover or mulching with dried grasses reduce attack levels and improve cabbage yield (CABI, 2000).
- Planting onions as trap crops around the borders and down the rows of cabbage protects cabbage from egg laying moths. Pull and destroy trap crops 2 weeks after they sprout. Plow-under, burn, or destroy all unwanted onions at the end of the harvests (Ellis; Bradley, 1996: p. 312).