Plant Health Initiative

Soybean Aphid

The 2008 Soybean Aphid Research Update is available to read online

The spiral-bound Soybean Aphid Management Field Guide for 2008 (CSI-11) is a new publication available from Iowa State University Extension

The soybean aphid (Aphis glycines) is a recently introduced pest of soybean. It is the only aphid in North America able to develop large colonies on soybeans.

When the tiny, sap-sucking insects are present in large numbers (several hundred per plant), their feeding can cause stunting, puckered yellow leaves, reduced pod set, and smaller seed.

Agronomic impact

Yield loss is related to aphid density at specific crop stages and on the condition of the crop. Risk of yield loss is greatest when aphid populations peak at beginning flower because of the impact on pod set. Damage due to aphid feeding increases when soybean growth factors, especially soil moisture, are below optimum. 

Factors influencing aphid populations

• Size of colonizing population from buckthorn in the spring
• Soybean variety
• Soybean plant health: aphid populations are higher on stressed plants.
• Aphid mortality from
  • predators, such as lady bug beetles, lacewing larvae, syrphid fly larvae, and minute pirate bugs
  • parasitic wasps that cause aphid mummies
  • fungal outbreaks
  • heavy thunderstorms
• Temperature
  • Optimum temperatures for aphid population growth are 75-80°F
  • Population growth will slow, stop, and may even decrease when temperatures are hot (greater than 90°F)

Aphids can transmit soybean viruses

A separate issue from the direct damage caused by aphid feeding is the ability of soybean aphids to spread virus particles from plant to plant as they feed. Soybean mosaic virus and other viruses are spread by soybean aphids in the North Central region. Virus infection in the early growth stages presents the greatest risk of yield loss and reduced seed quality, compared to infection later in the season.