Once corn plants reach the five to seven-leaf stage, they are large enough to escape damage by most seedling pests, says Buntin. Most insects of importance during the whorl stage defoliate the whorl and leaves. These include grasshoppers, armyworms, corn earworm, cereal leaf beetles and others.

Stalk-boring and root-feeding insects can be a problem on corn at mid-season, says Buntin. European corn borer, Southwestern corn borer and Southern cornstalk borer are caterpillars of moths that tunnel inside corn stalks during the whorl and ear fill stages.

 “Western corn rootworm is present in the northern two thirds of Georgia, but the insect continues to spread southward. Larvae feed on root tips causing root pruning reducing root activity, and yield potential,” he says.

Stink bugs can cause feeding damage to small developing ears before silking, says Buntin. “This type of feeding injury usually deforms ears into a C or boomerang shape. These ears fail to develop properly and are more susceptible to infection by corn smut fungus.”

Stink bugs, he says, are a perpetural problem on a variety of crops, moving from crop to crop as it enters fruiting and seed set. “In research looking at stink bugs using pheromone traps in corn, we focused on brown stink bugs. We found two populations, one in early June that corresponds with silking in corn, and a second population as the corn begins to mature and dry out.”

Resarchers, says Buntin, are looking at thresholds using various approaches. “Based on corn prices of about $4/bu., it’s one bug per two plants. With current prices being higher, the threshold is probably even less. Brown stink bugs are a lot harder to control than green. Methyl parathion has been our standard where it can be used. It will be phased out in 2013. At that point, at least with stink bugs in corn and in soybeans, we’re going to have some significant control challenges.”

Corn rootworm adults, Japanese beetles and grasshoppers can clip corn silks and interfere with pollination, says Buntin. Silk damage or removal by insect feeding can cause poor seed set and partially filled ears.

Damage must be severe, he says, to justify control with insecticides. Insecticidal control may be needed if most ears are infested, if silks are being clipped to within ½ in. of the ear tip, and one to two or more rootworms or Japanese beetles per ear are present.

Maize weevils naturally infest corn in Georgia as the crop matures in the field, says Buntin. “Timely harvest is the most effective tool for minimizing maize weevil infestations in the field. Insecticide control before harvest is not recommended in the field. Instead, corn should be treated as it is placed in storage and managed to reduce the temperature of the corn in storage.”