As small grains mature in late spring to early summer, winged females move to other wild or cultivated grasses for the summer. In the fall, they return to newly planted small grain fields to overwinter. Damage Aphids injure small grains by removing plant juices from the leaves, stems and grain heads. The greenbug secretes a toxic substance into the plants that kills plant tissue. Extensive feeding in the fall and early spring may result in circular yellow to brown spots with dead spots in the center.
Infested plants appear stunted and discolored.
A lack of moisture in midwinter and a cool spring result in more significant damage. The most significant damage occurs when large numbers of aphids feed on the grain head causing shriveled or blasted heads. All four species can also transmit barley yellow dwarf mosaic, a serious yield limiting virus. Aphid outbreaks are favored by a mild winter followed by a cool, dry spring. Under these conditions, aphids reproduce rapidly whereas their natural enemies reproduce slowly.