Because insect damage sometimes occurs below the soil surface, it may be difficult to determine the need for an insecticide. Seedcorn maggots are minor soil pests that sometimes cause stand loss by feeding on the germinating seed. There are no rescue treatments for this insect, so you must apply insecticides at planting time if economic damage is anticipated. Consider field history, previous crop or cover, heavy manuring during the spring, and cool weather conditions that may delay germination (like the snow and cold rain that fell at the end of April last year) when making your decision.
Seeds are at greatest risk for injury when animal manure is spread on the soil or when live, green plants are killed in the spring and incorporated into the soil prior to planting. The adult seedcorn maggot (a fly) is attracted to these areas of rotting vegetation to lay her eggs. Damage is more likely to occur during a cool, wet spring when germination is delayed. Fields that only have last years crop residue on the soil surface or are no-till fields should not have problems from seedcorn maggots. Germinating seeds alone are not sufficient to attract seedcorn maggots to the field.
If manure has been spread on the field or a green cover crop was disked or plowed this spring, a seed treatment containing both diazinon and lindane (such as Agrox D-L Plus or Kernel Guard) should provide protection. One packet of seed treatment (1.8 ounces of insecticide) will treat 50 pounds of either corn or soybean seed. A seed treatment is not necessary if a soil insecticide is being used for corn rootworms. Read and follow all label directions before using any insecticide.