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. While infestations that cause physiological yield loss are uncommon, some producers feel that the large number of aphids and the honeydew they produce may interfere with pollination by gumming up the tassels. Excessive honeydew on the tassels may limit pollen shed and it has been associated with barren corn, although this is very uncommon.