Is it Time to Spray Red Sunflower Seed Weevils?

Aug 22, 2025

By Adam Varenhorst and Patrick Wagner et.al

Red sunflower seed weevil adult activity is well underway on sunflowers in South Dakota. Compared to previous years, the red sunflower seed weevil populations are much lower during 2025. This is likely due to the general lack of snow cover that was present during our coldest weeks during the 2024-2025 winter. Even though the red sunflower seed weevil numbers are down, we are still observing populations in South Dakota that are above threshold (5-50 weevils per head versus the 1,000’s observed during the previous years).

As a reminder, current recommendations for management in both confection and oilseed sunflower is to begin treatment when the majority of the field has reached the R5.4 growth stage but applications done between R5.1 and R5.4 can still provide yield protection. The bigger issue is applying insecticides too early, as this leads to re-infestation and the need to reapply insecticides. Given the state of pyrethroid insecticide resistance in South Dakota, the timing of insecticide applications is critical to ensure additional selection pressure is not placed on other insecticides (i.e., malathion). Scouting and management for red sunflower seed weevil stops once most of the field has surpassed 70% pollination (R5.7). At this time, we do not recommend using lambda-cyhalothrin, esfenvalerate, zeta-cypermethrin, or deltamethrin active ingredients in South Dakota as past research as shown these products provide minimal reductions in red sunflower seed weevil populations. In addition, full labeled rates of insecticides should be applied. Beta-cyfluthrin has had variable management success in the past. A piperonyl butoxide synergist (PBO) may also be added to any of the insecticide active ingredients that are listed on the label of the PBO’s. In a laboratory setting, we observed some increases in mortality with the inclusion of a PBO. We also suggest considering adding crop oil to insecticide products that do not prohibit its inclusion on their label.

If you believe you have resistance to malathion during 2025, please reach out to Dr. Adam Varenhorst.

Identification

Adults

Red sunflower seed weevil adults are relatively small beetles (one-tenth to one-eighth of an inch long) that are a reddish-brown color. Like other weevils, they have mouthparts that extend forward beyond the head and form a snout (Figure 1). The antennae originate on this snout.

Red sunflower seed weevil adults are often present in fields prior to flowering and may be observed in the developing bud. Once flowering begins, they will move to the heads and often will crawl between the florets (Figure 2).

Larvae of the red sunflower seed weevil are cream-colored and relatively small. However, the larvae are not typically observed, as they feed directly on the developing seed (Figure 3).

Source : sdstate.edu

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