Evaluating the susceptibility of red sunflower seed weevils to pyrethroid insecticides

Since 2019, researchers at North Dakota State University and South Dakota State University have been evaluating the susceptibility of red sunflower seed weevils (RSSWs) to lambda-cyhalothrin and esfenvalerate using a laboratory assay with field collected RSSWs. From 2019-2021, zeta-cypermethrin was also included in the test. In 2022, sevin was evaluated. The results from these studies indicate that RSSW populations in South Dakota, are resistant to lambda-cyhalothrin, esfenvalerate, and have reduced susceptibility to zeta-cypermethrin (Mustang Maxx), and carbamate (Sevin LFR). The results also indicate that the geographic area of reduced susceptibility is expanding when compared to the initial assays. Although this may be an artifact of the increased number of fields that are now being surveyed annually. Results from 2023 indicate that deltamethrin (Delta Gold) was not effective at the majority of the sites that were tested. Beta-cyfluthrin (Baythroid XL) was effective at some of the sites that were tested, but also failed at others. These results may indicate that there is universal failure associated with the pyrethroid class of insecticides for red sunflower seed weevil management in South Dakota.