Seedcorn maggot

About

The larva of a small grayish-brown fly. The yellowish-white maggot, about a quarter inch long with a pointed head, eats into seeds and seedlings in cold, wet spring soil.

Spotting it

Damage

Seeds never come up, or when you dig them up they are hollowed out with a white maggot inside. It is worst on large-seeded warm-season crops such as corn, beans, peas and melons.

How to find it early

If a row comes up patchy, dig up a few seeds where nothing sprouted and look for maggots or hollowed seeds.

When

Early to late spring, especially when soil is cold and wet.

Life cycle

Pupae spend the winter in the soil, and flies emerge in early spring and lay eggs where they smell decaying manure, compost or plowed-in cover crops. There are two to four generations a year in Maryland (three to five in New York), and the early spring generations do the most harm.

What to do, gentlest first

Start at the top. Sprays are a last step; always read and follow the product label.

1. Plant into warm soil Prevent

   Wait until the soil warms, and sow seeds shallowly so they sprout fast. You can also pre-sprout corn, pea and bean seeds indoors before planting.

2. Let organic matter break down first Prevent

   Give a turned-in cover crop at least three weeks to decompose before planting, and avoid working in fresh manure right before sowing, since the smell of decay draws the flies.

3. Replant By hand

   If seeds fail, replant once the soil is warmer.

4. No home-garden spray Conventional spray

   Commercial growers use insecticide-treated seed or transplant drenches (Cornell). For home gardens, timing and soil prep are the practical tools.

   Treated seed may carry insecticides such as neonicotinoids or spinosad (Cornell); handle it with gloves, keep it away from children, pets and birds, and never eat it.

Plants it goes after

Asparagus, Beet, Cabbage, Cantaloupe (muskmelon), Cucumber, Dry beans (pinto, black, kidney, navy), Edamame, Green beans (snap beans), Onion, Peas, Potato, Radish, Spinach, Sweet corn, Turnip, Watermelon, Winter squash and pumpkin, Zucchini and summer squash

Pressure by region

It is a spring pest of cold, wet soils; Cornell and Maryland Extension cover it in the Northeast. No regional severity source was found, so the moderate ratings for the Midwest and Great Plains and all low ratings, including Alaska and Hawaii, are estimates.

Ratings come from extension sources where available; some are estimates, as noted above.