By Scout Nelson
Red sunflower seed weevil activity is underway in sunflower fields across South Dakota, but 2025 populations are much lower compared to previous years. Experts believe this decline is linked to the lack of consistent snow cover during the coldest weeks of the 2024–2025 winter, which likely reduced weevil survival.
Despite the smaller numbers, many fields still have weevil counts above treatment thresholds, ranging from 5 to 50 weevils per sunflower head. Although these figures are far below the thousands observed in past seasons, growers must remain alert.
Current management advice for both confection and oilseed sunflower crops is to begin insecticide applications once most of the field has reached the R5.4 growth stage. However, treatments made between R5.1 and R5.4 can still help protect yields. Applying insecticides too early poses a bigger problem, as it often results in re-infestation and the need for multiple applications.
Given the growing resistance of weevils to pyrethroid insecticides in South Dakota, careful timing of applications is essential. Experts warn against relying on products with active ingredients such as lambda-cyhalothrin, esfenvalerate, zeta-cypermethrin, or deltamethrin, since past research has shown these provide minimal control.
Instead, farmers are encouraged to use full labeled rates of approved products. Beta-cyfluthrin has shown mixed results, while the use of a piperonyl butoxide (PBO) synergist may improve effectiveness in some cases.
Adding crop oil to insecticide mixtures may also boost results, provided product labels allow its use. Scouting should continue until most of the fields surpass 70% pollination.
Categories: South Dakota, Crops, General