Written collaboratively by Adam Varenhorst, Philip Rozeboom, Zachary Loomis, Patrick Wagner, and Brad McManus.
During the 2023 and 2024 growing seasons, researchers at SDSU surveyed soybean in Eastern South Dakota for the presence of Dectes stem borer adults (Figure 1). Each field was sampled using a sweep net. During 2023, sampling started in early June and continued through the end of June. During 2024, sampling was initiated in late June and continued through July. In 2023, fields in 35 counties were sampled and during 2024, 25 counties were surveyed. In each county, the number of fields surveyed varied from 1-5.
In 2023, Dectes stem borer adults were detected in five counties (Bon Homme, Clay, Douglas, Turner, and Yankton) and a total of nine adult Dectes stem borer were collected. During 2024, Dectes stem borer adults were collected from 15 counties (Aurora, Beadle, Bon Homme, Brule, Charles Mix, Clark, Clay, Douglas, Hanson, Hutchinson, Jerauld, McCook, Turner, Union and Yankton). In 2024, a total of 332 Dectes stem borer adults were captured. Differences in the number of adults captured between the two years are likely due to the timeframe when survey samples were collected.
The counties with the highest Dectes stem borer counts in 2024 were Bon Homme (67 adults collected), Charles Mix (32 adults collected), Clay (33 adults collected), Hutchinson (32 adults collected), Turner (106 adults collected) and Yankton (16 adults collected). The highest average number of adults per field was Turner County with an average of 26.5 adults collected per field.
Scouting for Dectes stem borer in soybean should begin in late June and continue through July to ensure that adults are not missed. Soybean fields present in counties where Dectes stem borer were detected during 2024 should be closely monitored for adult presence.
