Soybean aphid in Minnesota soybean
Photo: Adam Sisson, Iowa State University, Bugwood.org
Photo: Christina DiFonzo, Michigan State University, Bugwood.org
Figure 1. Wingless adult showing cornicles, on soybean (top) and winged and wingless adults on buckthorn (bottom).
Soybean aphid (Aphis glycines)
Adults (Figure 1)
- Small (1/16th inch long), pear-shaped bodies
- Black cornicles ("tailpipes") at the end of the abdomen
- Piercing-sucking mouthparts tucked under head
- Both winged and wingless morphs may occur on soybean
Eggs are not found in soybean.
- Nymphs are similar to wingless adults, but smaller. White "flakes," which are the molted skins, may be present near aphids.
The soybean aphid life cycle is complex. Aphids overwinter as eggs on buckthorn in wooded areas. In spring, eggs hatch and several generations of aphids are produced without mating. Winged aphids are eventually produced on buckthorn, which then fly to soybean fields. Numerous generations of both winged and wingless aphids are produced on soybean without mating during the summer. In fall, aphids return to buckthorn where they mate and deposit eggs, which subsequently overwinter.
Soybean aphids use their piercing sucking mouthparts to extract plant sap. Feeding by soybean aphid can reduce soybean yield and quality. Yield can be further reduced when heavy infestations result in dark sooty mold (Figure 2), which grows on the sugar excretions of aphids. Soybean aphids also transmit viruses to soybean.
Scouting and management
Early in the season, pay particular attention to fields in areas with abundant buckthorn, smaller fields with wooded borders, and/or early-planted fields. At this time of year, soybean aphids will typically be found on the new growth. The presence of lady beetles or ants on soybean plants is often an indicator of the presence of early-season aphid colonies. Later in the season, aphids are more commonly found throughout the canopy of the plant.
- Sample at least 20-30 plants per field.
- Aphid counts should include winged and wingless aphids, but don't count dead aphids or aphid look-alikes (see Scouting for soybean aphid for photos of look-alikes and predators).
- Infested fields should be scouted every 7-10 days. When populations are increasing rapidly, monitor more frequently.
- Continue scouting until R6.5 (pods and leaves begin to yellow).
A complete description of scouting, including a more efficient scouting method called Speed Scouting, and management can be found in the Extension publication, Scouting for soybean aphid.
From vegetative through R5 (seeds developing, but pod cavity not filled), consider treating when:
- Average counts exceed 250 aphids per plant, AND
- more than 80 percent of the plants are infested, AND
- aphid populations are increasing.
This threshold is based on multiple years of university research.
Yield loss can occur into the early R6 growth stage (when a pod on one of the four top nodes has green seeds that fill the pod), but larger numbers of aphids are required to cause losses. Therefore, consider treating if aphid populations are very large in early R6 and plants are experiencing other stresses.
Winston Beck, Iowa State University, Bugwood.org
Figure 3. Ladybeetle larva feeding on soybean aphids.
Labeled rates of foliar insecticides can be used to manage soybean aphids (follow directions on the product label). Only use insecticides when necessary to reduce the risk of insecticide resistance. For more information, see Insecticide resistance management in soybean.
Neonicotinoid seed treatments are typically not a reliable tactic because aphids typically colonize fields after insecticide concentrations in plants have decreased to non-effective levels. However, seed treatments may be considered for fields that are at high risk for early infestation or are late planted (soybeans after peas).
Aphid resistant soybean varieties can be effective, but availability of well-adapted varieties is limited (see Aphid-resistant soybean varieties for Minnesota).
Many beneficial organisms, such as predators, parasitoids and fungal diseases, help suppress aphid populations (Figure 3). Use of scouting and the economic threshold (described above) will help conserve these beneficial organisms.
Aphid-resistant soybean varieties for Minnesota – University of Minnesota, 2016
Just the facts: A review of the biology and recommendations behind soybean aphid insecticide recommendations – Multi-state University review, 2016
Scouting for soybean aphid – University of Minnesota, 2015