By Scout Nelson
Red sunflower seed weevils are becoming active in sunflower fields, making this an important time for growers to begin scouting. These insects can damage developing seeds and reduce both crop yield and seed quality if populations become too high. Regular field monitoring helps producers determine when treatment is necessary and prevents unnecessary insecticide applications.
Adam Varenhorst, Associate Professor & SDSU Extension Field Crop Entomologist, together with Philip Rozeboom, Patrick Wagner, and Brad McManus, encourages producers to scout sunflower fields carefully and apply insecticides only at the recommended growth stages. Proper timing protects yield while helping slow the development of insecticide resistance.
Adult red sunflower seed weevils are small reddish-brown beetles with a long snout and bent antennae. They often appear before flowering and move onto sunflower heads as they begin blooming.
Their cream-colored larvae develop inside sunflower seeds, where they feed without being easily seen.
Scouting should begin when sunflower plants reach the R4 growth stage, when yellow ray petals first become visible, and continue until about 70% pollination is complete, known as the R5.7 stage. Growers should inspect 25 plants from several areas of the field by walking about 75 feet into the field at each location.
Gently rubbing the sunflower head helps disturb adult weevils, making them easier to count. Aerosol insect repellent can also be used to encourage adults to emerge for counting.
Treatment decisions depend on the number of adult weevils found and the type of sunflower being grown. Oilseed sunflower fields generally require treatment when four to six adult weevils are present per head.
Confection sunflower fields have a much lower threshold of one adult weevil per head because of the higher value of the crop.
Researchers also remind growers not to apply insecticides too early, as early sprays can allow fields to become reinfested and may require additional applications. Several pyrethroid insecticides no longer provide reliable control in South Dakota because of resistance. If resistance to malathion is suspected during the 2026 season, growers are encouraged to contact SDSU Extension.
Because insecticide applications occur during flowering, producers should protect pollinators by spraying early in the morning or later in the evening when bees are less active.
Photo Credit: pexels-ekamelev
Categories: South Dakota, Crops