D3464: Determining the distribution of Dectes stem borer in South Dakota soybeans

Tuesday, November 12, 2024

9:00 AM – 5:00 PM MST

Location: Phoenix Convention Center, Exhibit Hall 6, PCC

Presenting Author(s)

ZL

Zachary Loomis

South Dakota State University
Bruce, South Dakota

Co-Author(s)

PR

Philip Rozeboom

IPM Coordinator
South Dakota State University
Brookings, South Dakota
BM

Bradley L. McManus

South Dakota State University
Brookings, South Dakota
Adam J. Varenhorst

South Dakota State University
Brookings, South Dakota

The Dectes stem borer (Dectes texanus) is an insect native to North America that is generally considered a minor pest of soybean (Glycine max) in much of the Midwest and Northern Great Plains. This is due to its historically sporadic infestation of fields and absence in many growing areas. However, since 2017 there have been increasing occurrence and severity of Dectes stem borer infestations in soybean noted in southeastern South Dakota. Dectes stem borer larvae cause 12% yield loss due to feeding within the stem and girdle the plant causing it to lodge. Due to the extended period of adult emergence from June through August, it isn’t recommended to manage Dectes stem borer adults using foliar insecticides, although there is research that suggests it is possible. Cultural control recommendations include tillage, crop rotation, and management of alternative weedy hosts. The purpose of this research was to develop foliar insecticide management recommendations for Dectes stem borer. Field sites near Freeman, Menno, and Tabor South Dakota were selected based on previous Dectes stem borer pressure. At each site, foliar insecticides were applied during the second and fourth week of July. A total of nine treatments were tested, of which only four are labeled for Dectes stem borer management in South Dakota. Although there were no significant yield differences in 2023, two treatments improved yield slightly. These results may indicate that the yield loss caused by Dectes can’t be distinguished statistically in the absence of lodging.