Soybean Aphids

Soybean aphids are small, yellow aphids with distinct black cornicles (“tail-pipes”). At only 1/16th of an inch long (the size of a pinhead or smaller), they cannot be distinguished from other aphids with the naked eye. The soybean aphid is the only aphid in North America known to extensively colonize soybean fields.

Soybean aphids have needle-like sucking mouthparts, which they insert into soybean tissues to remove plant sap, causing leaves to wilt and curl. From the seedling stage until blooming, aphids colonize tender leaves and branches of the plant. Later, the aphids move down to the middle or lower parts of the plant, and tend to colonize the underside of leaves as well as the stem. If aphid numbers are high, leaves may become yellow and distorted, the plant may become stunted, and plant parts may be covered with a dark, sooty mold. Yield losses often accompany these symptoms. The soybean aphid is capable of transmitting virus diseases to soybeans, which can cause leaf mottling, various leaf, pod and plant deformities, stunting, and discolored seed. Virus development usually results in yield losses.

Soybean aphids overwinter as eggs on a woody shrub species known as buckthorn. The eggs hatch in the spring into wingless types, which establish on buckthorn for two generations. The third generation emerges, produces wings and migrates to soybean fields and other acceptable hosts.

The soybean aphid can produce up to 15 generations during the summer on soybeans before migrating back to buckthorn in the fall as winged females. Once on buckthorn the winged females give birth to wingless females, which mate with males developed on soybeans to produce the overwintering eggs.

The soybean aphid can produce up to 15 generations during the summer on soybeans before migrating back to buckthorn in the fall as winged females. Once on buckthorn the winged females give birth to wingless females, which mate with males developed on soybeans to produce the overwintering eggs.

Soybeans at risk to aphid injury include all fields in areas where aphids were detected the previous year or the current year. The northern states bordering the Great Lakes have the highest annual probability of aphid infestations. In addition to geographical considerations, soybean fields at highest risk include those planted late and those that experience hot, dry weather that stresses the crop.

Because populations can increase rapidly, growers should scout regularly, monitor aphid populations and be prepared to treat if necessary. The recommended time to begin scouting is when soybeans are in the late vegetative stage (usually late June/early July in Midwest states). Growers should continue their watch through pre-flower and flowering stages and treat if aphids become abundant throughout the field

Management decisions regarding soybean aphids are difficult due to the explosive potential of aphid populations and the interaction of aphids with climatic conditions and natural predators (e.g., lady beetles and their larvae). Scout carefully to determine if treatment is needed and to time insecticide treatments to maximize their effectiveness. Economic threshold (ET) guidelines are currently established at 200 to 250 aphids/plant. These thresholds have been established using an Economic Injury Level (EIL) of 400 to 500 aphids per plant. Insecticides labeled and most commonly used for control of soybean aphids in soybeans include Asana XL, Penncap-M, MustangMAX, Lorsban 4E, Pounce 3.2EC and Warrior.

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