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| Symptoms of direct feeding include stunting and yellowing of leaves. |
Go to the following pages to study:
Description, identification, and the life cycle of soybean aphids
Symptoms and signs of aphid activity
Scouting soybean aphids
Management of soybean aphids
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Agronomic Impact of the Soybean Aphid
Soybean aphids may be small, but when they multiply in large numbers during the season, their collective feeding can cause severe damage to soybeans. Plant injury may be more subtle and harder to detect than injuries caused by insects with chewing mouthparts, such as grasshoppers and bean leaf beetles. The soybean aphid has syringe-like mouthparts that suck the sap out of soybeans. Soybean aphids cause damage directly by sucking plant sap and transmitting viruses and indirectly by creating an environment for sooty mold that will reduce photosynthesis.
Plant injury
Although experience with the soybean aphid in the U.S. is limited, symptoms of direct feeding damage may include plant stunting, pod and flower abortion, reduced seed size and seed counts, and puckering and yellowing of leaves. The soybean aphids colonize “tender” leaves and branches as early as the seedling stage. Later as the growing point slows, the aphids slow their reproductive rate, move down to the middle and lower part of the plant, and feed on the undersides of leaves, stems, and pods.
Yield loss
Yield loss caused by aphid is variable, and it can be influenced by many factors, including aphid numbers, virus transmission, weather, natural enemies, and variety selection. On-farm strip trials from Iowa in 2003 showed up to 18 bu/acre yield differences between an insecticide-treated strip and a non-sprayed strip in an aphid-infested field. Reports from other states have been as high as 25 bu/acre yield loss from soybean aphids. Aphids have no apparent effect on oil or protein content of the soybeans.
Soybean aphids transmit soybean viruses
Soybean aphids are also capable of transmitting viruses that can cause soybean diseases, such as Soybean Mosaic Virus (SMV) and Alfalfa Mosaic Virus (AMV). The role of soybean aphid in the transmission of soybean virus is not well understood. Currently, we can not determine with accuracy how much of the yield loss is due to aphid feeding versus soybean viruses that the aphids may have transmitted. However, research is underway to determine that.
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