University of Illinois

No. 9/May 23, 1997

Insecticide Seed Treatment on Soybeans: A Wise Investment in Plowed-Down Alfalfa

This past week, a grower indicated that a field of soybeans would require replanting due to severe injury caused by seedcorn maggots. The soybean field had been devoted previously to the production of alfalfa. The alfalfa stand was plowed under and soybeans planted without any insecticide being used as a seed treatment. Under these conditions, the decaying alfalfa acted as a sink for adult seedcorn maggot flies, and numerous eggs were most surely deposited in the field. My recommendation to the producer: Consider the use of a seed treatment containing the active ingredient lindane during the replant operation. Recall, diazinon is no longer labeled for use as an insecticide on soybean seeds.

Seedcorn maggots and cotyledon injury.

More tidbits on seedcorn maggots (Metcalf, Flint, and Metcalf, 4th edition, 1962):

€Seedcorn maggots have a wide host range, including corn, beans, peas, cabbage, turnip, beets, radish, potatoes, and most certainly many more crops.

€Seedcorn maggots were first reported in the United States (New York) in 1856.

€Overwintering is most likely accomplished as a larva within a puparium (1/5 inch long).

€Eggs can begin hatching at 50 degrees F.

€Larvae and pupae can continue development within a temperature range of 52 to 92 degrees F.

€The life cycle can be completed in about 3 weeks.

€Three to five generations occur annually within the Corn Belt.

€Fields that receive manure applications are most susceptible to seedcorn maggot infestations.

Mike Gray, Extension Entomology, (217)333-6652