Figure 1. Soybean aphid colony. Credit: A. Varenhorst
While scouting soybean last week, we noticed that aphid populations near Volga, SD were steadily increasing from the previous week (Figure 1). Although the soybean aphids in the field are still well below the economic threshold of an average of 250 aphids per 20 plants, there were a few hotspots that will be monitored in the following weeks. Our peak count was 376 soybean aphids on a single plant. However, the average for the field was 39 soybean aphids per plant. Soybean aphids are typically more of an issue later in the season (July-August), but their populations are already present and steadily increasing. It will be important to not delay and start scouting within the next week to prevent any surprise outbreaks from occurring.
At this point, we have not observed populations in other areas of the state. Soybean fields that border shelterbelts or groves should be given a higher priority when scouting for soybean aphids. These areas may harbor buckthorn, resulting in soybean aphid infestations earlier in the season. If populations of soybean aphids are observed, scout and follow the recommended threshold of a 250 soybean aphid average based on 20 plants.