Figure 1. Red and gray sunflower seed weevils on a sunflower bud.
Credit: R. Beck
Red Sunflower Seed Weevil Update
A couple of weeks ago, we covered red sunflower seed weevil scouting. Last week, we received calls regarding this pest and the population reports were staggering. The recommended threshold for the red sunflower seed weevil is 4-6 adult weevils per head (Figure 1). However, the populations that are being observed in South Dakota are approximately 40-100 adults per head. Even more beetles were seen, but counting was stopped due to the threshold already being greatly exceeded.
In addition to the large populations, we also received reports of issues regarding the management of the red sunflower seed weevil. Thus far, reports indicate that products containing lambda-cyhalothrin haven’t been reducing red sunflower seed weevil populations. Although this may be an issue of resistance towards the active ingredient, we haven’t been able to confirm this. When spraying for red sunflower seed weevils, the chemical application should be oriented to obtain maximum coverage on the face of the sunflower head. Be sure to follow the recommended label rates for insecticides to ensure that the appropriate amount of active ingredient is being applied.
If you have a sunflower field with a population of red sunflower seed weevils that didn’t respond to an application of a product containing lambda-cyhalothrin, please contact us at SDSU Extension so that we may collect a sample. If these populations are resistant, early detection will be important to prevent additional insecticide applications and also to ensure yield protection.