The seedcorn maggot is the larvae of a fly, says Eric Sideman, MOFGA’s organic crop specialist, in the fall issue of The Maine Organic Farmer & Gardener. He continues: This critter spends the winter as a pupa in the soil. Flies emerge very early in the spring from these pupae and lay eggs near decaying organic matter and germinating seeds. The eggs hatch into maggots that feed on the seeds or young plants. Gaps in rows of crops such as onions, spinach, corn, peas, etc., often blamed on poor seed, actually result more often from seedcorn maggot feeding. The fly is often attracted to decaying organic matter, including some fertilizers that organic farmers use, such as soybean meal. In such cases the maggots end up feeding on the seeds and seedlings.
Fall is the time to start thinking about managing this pest because the pupae that overwinter come from eggs laid in the fall. Row covers put on in the spring, just after seeding or transplanting, may keep new seedcorn maggot flies from coming into your field, but they won’t work if the pupae are already in the soil that you are covering. These flies will emerge under the cover and lay eggs that result in maggots happily feeding on your crops. To avoid this issue, avoid adding attractive organic matter (e.g., manure, lush cover crops, etc.) in the fall to soil in fields that you plan to use for early spring crops.