Soybean aphid season under way
University of Nebraska researchers are beginning to get reports of soybean aphids in southwest Minnesota and South Dakota. The numbers are low, but relatively widespread.
There have only been a couple reports of soybean aphids in Nebraska, again at very low numbers, but this is when we generally start to find them.
Start scouting now, as populations can start late and build fast. In 2011 we monitored a soybean field in Dixon County that was almost devoid of aphids on July 22, but by August 18 was over 2000 aphids per plant in untreated field areas.
Soybean Aphid Description
The soybean aphid is soft-bodied, light green to pale yellow, less than 1/16th inch long, and has two black-tipped cornicles (cornicles look like tailpipes) on the rear of the abdomen. It has piercing-sucking mouthparts and typically feeds on new tissue on the undersides of leaves near the top of recently colonized soybean plants. Later in the season the aphids can be found on all parts of the plant, feeding primarily on the undersides of leaves, but also on the stems and pods.
Soybean Aphid Life Cycle
The seasonal life cycle of the soybean aphid is complex with up to 18 generations a year. It requires two species of host plant to complete its life cycle, common buckthorn and soybean. Common buckthorn is a woody shrub or small tree and is the overwintering host plant of the aphid. Soybean aphids lay eggs on buckthorn in the fall. These eggs overwinter and hatch in the spring, giving rise to wingless females. These females reproduce without mating, producing more females. After two or three generations on buckthorn, winged females are produced that migrate to soybean.
Multiple generations of wingless female aphids are produced on soybeans until late summer and early fall, when winged females and males are produced that migrate back to buckthorn, where they mate. The females then lay eggs on buckthorn, which overwinter, thus completing the seasonal cycle. Nebraska lacks significant and widespread buckthorn populations, and so early season soybean colonization by aphids migrating from buckthorn appears to be limited.
Soybean aphid populations can grow to extremely high levels under favorable environmental conditions. Reproduction and development is fastest when temperatures are between 70° and the mid 80°s. Aphid numbers can change rapidly (populations can double in two to three days). The aphids do not do well when temperatures are in the 90°s, and are reported to begin to die when temperatures reach 95°. When temperatures drop below 48°, development stops.