Corn disease: what are seed corn maggots?

What is it?

Seedcorn maggots or hylemya platura, are known as such because they feed on the seeds and seedlings of corn plants. As seedcorn maggots can prodice several generations in a year it is important to treat them before populations get out of control and ruin and prospect of a harvest.

Seedcorn maggots are white worms that have a pearly sheen to them. Typically the grow to only about 1/4 inch long. Seedcorn maggots feed on the seeds of the corn, hollowing them out until they become dry and brittle. Seedcorn maggots also feed on the seedlings which are weak to begin with, weakening them further until the seedlings either die off or grow poorly without producing any leaves. Often the presence of seedcorn maggots is only known because several areas with good corn seeds never sprout, having been hollowed out by these pests.

How does it manifest?

Seedcorn maggots in adult form are black, hairy flies. These adult flies in their female form lay eggs in the soil or surrounding organic matter. Maggots then emerge from the soil and feed on the seeds by burrowing into them and eating the inner tissue, effectively hollowing out the seeds and leaving nothing but a hollow shell of the seed. Damaged seeds which are still viable can be further damaged by diseases such as black rot entering the wounds made by seedcorn maggots. After feeding, the maggots pupate in the soil and emerge as the adult flies which then feed on the plant itself, sucking it’s nourishing juices and weakening the plants that have grown. You will find seedcorn maggots most prolific in cool periods, or in areas where there is a lot of organic material in the soil. Seedcorn maggots also survive in their pupal stage over the winter in the soil, and can produce several generations in a growing season.

What can you do about it?

Prior to planting, you can treat seeds with an insecticide powder which contains diazinon. The commonly used proportion is 1/4 teaspoon diazinon to a seed packet. Once you’ve powdered the seeds you will need to shake off excess insecticde and plant the seeds 1.5 to 2 inches deep in the soil. Avoid adding organic fertilizers as that’s what seedcorn maggots are attracted to. Also note that seedcorn maggots will feed similarly on beans and peas in addition to corn.