Plant Health Initiative

Soybean aphid - agronomic impact

 

Signs of aphid feeding. Click on image to view a larger version. Photo credit: University of Wisconsin

The impact of aphids on yield depends how many aphids are feeding and when. Soybeans are most at risk for yield loss when aphid populations increase quickly during R1- to R4 growth stages, when blooms and young pods are most susceptible to stress.

Aphid populations tend to be higher and more damaging in fields or parts of fields where plants are already stressed from dry soil, soil fertility factors, weather conditions, other diseases, or in fields that are planted late. Scout these fields most closely.

 

Factors influencing aphid populations

Aphid populations vary widely from year-to-year and field to field, depending on

• Size of colonizing populations from buckthorn in the spring
• Soybean variety planted - varieties can differ in their ability to tolerate aphid feeding or support aphid development
• Soybean plant health
• Aphid mortality from natural enemies, including
  • predators, such as lady bug beetles, lacewing larvae, syrphid fly larvae, minute pirate bugs
  • parasitic wasps (parasitoids)
  • fungal outbreaks
• Environment
  • 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)
  • Heavy thunderstorms can knock back populations

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 diseases, such as soybean mosaic virus, from plant to plant as they feed.

Virus infection that occurs in early growth stages presents the greatest risk of yield loss and reduced seed quality, compared to infection later in the season.

 

Resources

Ecoonomic Impact of the Soybean Aphid - Integrated Plant Management newsletter, ISU