Soybean Management Guide

Soybean Aphid

The soybean aphid (Aphis glycines) is a soft-bodied insect, light green to pale yellow, less than 1/16th inch long. It also has two black‐tipped cornicles (cornicles look like tailpipes) on the rear of the abdomen (Figure 1). This insect has a piercing‐sucking mouthparts and is typically found feeding on new tissue on the underside of soybean leaves. With severe infections later in the growing season, aphids can be found feeding on all plant parts. The soybean aphid is the only aphid currently known to colonize on soybean in the North America.

The soybean aphid life cycle is complex with up to 18 generations a year. For the life cycle to be completed, it requires two plant host species — common buckthorn (Rhamnus cathartica) and soybean. Common buckthorn serves as an overwintering host plant for the aphid. Adults lay eggs on the buckthorn in the fall and these eggs overwinter and hatch the following spring to wingless females. These females start reproducing without mating, giving rise to more female aphids. Once two to three generations are produced on buckthorn, winged females are produced that migrate to soybean.

Once on soybeans, multiple generations of wingless female aphids are produced until late summer and early fall. When daytime high temperatures are between 70‐85°F, aphid populations can increase dramatically (populations can double in two to three days). When daytime high temperatures are between 90°F and 95°F, reproduction decreases, and when daytime high temperatures are above 95°F, death occurs. If high populations are reached during the summer, winged females are again produced that migrate to other soybean fields.

Conventional Method

Conventional Method — Check 20 to 30 randomly selected plants for the presence of aphids in four to five areas in the field. Particular attention should be placed on checking areas of fields adjacent to tree lines where wind-blown aphids are more likely to settle. When checking the plants, concentrate on checking the upper portion where aphids typically first colonize. Record the total number of aphids per plant checked and determine an average number for each area checked.

Speed Scouting Method

Speed Scouting Method — This method uses a spreadsheet that has been adapted from a sampling plan developed by the University of Minnesota. Plants are considered “infested” when there are 40 or more aphids on a plant. The scout does not have to count or estimate the number of aphids on a plant to determine where it has reached threshold of 250 aphids per plant. The spreadsheet then recommends further scouting or treatment options based on the number of “infested” plans in a given area.