Infestations become apparent when the tassels begin to emerge revealing colonies of aphids.
Infestations are more common in late-planted corn. Corn is most susceptible to yield loss by aphids while in the whorl stage. If large numbers are present three weeks before tassel emergence, physiological damage and some yield loss may occur. Corn may be stunted or wilted, especially when plants are under drought or nutritional stress. However, infestations usually occur close to tassel emergence, and despite large numbers of aphids, don't cause economic losses.