Fungi in the soil can kill the embryos of corn seeds before they germinate, and seedlings may be infected by more fungal diseases. Corn seeds planted in cold, wet soil are especially at risk. There is no way to measure the numbers of insect pests before soil is planted. Granular soil insecticides applied when the corn is planted are expensive, potentially hazardous, environmentally unfriendly, hard to handle and apply--and they do not work very well. An alternative is to treat seeds before planting them.
Commercial seed producers and processors treat corn seeds with fungicides or a combination of fungicides and insecticides to protect them when they are germinating and when seedlings emerge. The treatment of seeds to prevent infestations of insects has lately been added to protection against fungal diseases.
Fungal Disease Prevention
Horticulturalists at Iowa State University report two seed treatments have been used traditionally to control fungal diseases. One is a combination of the active ingredients fludioxonil and mefenoxam. The second combination uses the active ingredients captan and metalaxyl with a polymer coating on the seed. Fludioxonil and captan are broad-spectrum fungicides used to control fungi that include Fusarium and Rhizoctonia. Mefenoxam and metalaxyl are narrow-spectrum insecticides used to control Pythium. Treating seeds with fungicides will not control corn smut, leaf blight, rots of stalks and ears or viral diseases.
Corn plants are the target of numerous insects--including larval and adult beetles, billbugs, corn root worms, flea beetles, seed-corn beetle, thrips and white grubs. Horticulturalists at North Carolina State University recommend seeds that are treated with neonicotinoids to control insects. Neonicotinoids block neural pathways that are abundant in insects; they are selectively toxic to insects, not humans and other mammals. Corn seeds are easily treated with water-soluble neonicotinoids, plus they are not expensive to apply and are environmentally friendly.
Neonicotinoid Treatment Studies
Studies conducted by North Carolina State University show that treating corn with products containing the active ingredient clothianidin, a neonicotinoid, performed better against the southern corn billbug compared to those insecticides containing the neonicotinoids imidacloprid or thiamethoxam. NC State tests concluded that corn seed treatments containing clothianidin and thiamethoxam were more effective against wireworms than those containing imidacloprid. Tests showed that treatments containing clothianidin and thiamethoxam were both effective against cutworms if applied at rates recommended by the manufacturers.
The U.S. Department of Agriculture National Organic Program does not permit chemically treated corn seed for certified organic agriculture. The French government does not allow neonicotinoid treatment of seeds because it believes the use of neonicotinoids are implicated in the dramatic drop in the population of bees needed for pollination and possibly in a disorder that causes bee colonies to collapse.