Quick Steps to Slow Spread of Soybean Aphid Resistance

More than 100 soybean aphids collect on the underside of a soybean leaf. Pest feeding can inhibit the plant's ability to make grain, or kill it outright.

The number one soybean insect pest is growing across the Upper Midwest. Recent reports indicate some aphid populations are developing resistance to insecticides, especially pyrethroid products.

While we may not be able to stop the spread of this resistance, we can certainly slow it down by using these best management practices:

  • Avoid spraying any insecticide if the economic threshold has not been reached. The accepted economic threshold is 250 aphids per plant in 80% of the field as long as the aphid population is increasing. This should not be confused with the injury threshold, which ranges from 600 to 700 aphids per plant. The economic threshold is designed to give farmers time to apply insecticide before the field reaches the injury threshold.
  • Use insecticides with different modes of action just like we use herbicides with different modes of action to help control resistant weeds. Some common examples of pyrethroid products include Warrior®, Mustang®, Asana®, Baythroid® and Pounce®, as well as a host of generic products. Lorsban® is an example of an organophosphate insecticide that may be used for aphid control.
  • Avoid adding insecticide to herbicide application just as “insurance” or to save a trip across the field, as this can easily lead to resistance problems.
  • When applying insecticides, good coverage is essential. Higher spray volumes and pressure help to move the product down into the soybean canopy.
  • As with many potential threats, scouting early and often is crucial to overall success!Soybean aphids can greatly increase in numbers if the weather is cooler than normal and if natural predators are not present.

First identified in Wisconsin during the summer of 2000, soybean aphids are found in 21 states and three Canadian provinces. Besides the damage they do by sucking sap from plants, aphids also are vectors of several viruses that attack soybeans.

Scouting for aphids is key for maintaining the health of your soybean crop now… and in the future. Do what you can now to keep numbers down and to avoid insecticide resistance from building.