The seedcorn maggot (Delia platura) is a pest of many vegetable crops such as cabbage, broccoli, turnip, radish, onion, beet, spinach, pepper, potato, beans and peas. Maggots usually feed on germinating seeds, roots or stems, resulting in reduction of seedling stands and contamination of the crop. They also occasionally feed on head lettuce to make it unmarketable (the maggots damaging spring head lettuce were officially identified as seedcorn maggots. For more information, please visit http://ucanr.org/blogs/SalinasValleyAgriculture/index.cfm?start=16, Spring Head Lettuce Crop Affected by Insect, Thursday April 29 2010). The damage is especially severe during cool and wet winter or spring, and in fields with high organic matter. The feeding damage often causes secondary infections by pathogen.
The seedcorn maggot overwinters as pupa in soil. The adult emerges in early spring and a female can lay an average of 270 eggs in the soil near plant stems. The female prefers to lay eggs in fresh-tilled soil with high moisture and organic matter. The eggs hatch in a few days and the maggots feed for 1 to 3 weeks on decaying organic matter or their host plants before pupation in soil.
Prevention is the best management strategy for this pest. Any cultural practice to speed up seed germination and plant growth will help to reduce crop loss. Attach drag chains behind the planter during seeding can reduce egg laying in the seed row. Fields with heavy manure or cover crop should be plowed at least 2 weeks before planting. Fields with a history of seedcorn maggot problem may apply an insecticidal seed treatment at planting. After damage is observed on the crop, rescue treatments are usually not effective. Prompt resetting or replanting of the damaged crop may be necessary if stand loss is severe.