Soybean stunting caused by soybean aphids: Soybean plants (left) stunted by soybean aphids and sprayed soybean plants (right). (Photo Marlin E. Rice)
Black sooty mold on soybean: Honeydew and sooty mold cover these soybean leaves infested with soybean aphids. (Photo Marlin E. Rice)
Soybean stunting caused by soybean aphids: A soybean field near Decorah, Iowa with soybean rows sprayed (greener and fuller) and unsprayed (darker with uneven plant height). (Photo Marlin E. Rice)
Soybean aphids injure soybean by removing nutrients from the plant. Colonies grow at a very fast rate (the population size doubles every 2-5 days) because colonizing aphids are all female and give birth to live young. The excreted waste from these aphids is called honey dew and contains mostly sugar (such as melezitose; an attractant for ants [Chapman 1998]). These sugars also coat the lower leafs of the plant and provide a medium for the growth of black sooty mold. This further reduced the photosynthetic potential of the plant, resulting in stunted plant growth. See Soybean Aphids in Iowa–2007 for more information and management recommendations.
Aphid-transmitted viruses can be an important part of the ecology of aphids (Hull 2002, Donaldson and Gratton 2007). This is particularly true for aphid behavior with some plant-virus infections, which attract aphids to some plants (Hull 2002) while some plant viruses are antagonistic to aphid population growth (Donaldson and Gratton 2007). The latter case apparently occurs with the soybean aphid and three RNA viruses (Soybean mosaic virus, Alfalfa mosaic virus, and Bean pod mottle virus) in soybean. Field plots infected with these three viruses have much lower in aphid abundance than uninfected plots (Donaldson and Gratton 2007).