Considerations for properly timed foliar treatments include stem weevil development, crop development and stem weevil counts. Fall tillage that destroys the overwintering chambers at the base of the stalks has also been recommended but may not be compatible with soil conservation practices. Delay Planting to Avoid Sunflower Stem Weevil Damage Planting after June 1 results in sunflower plants that are too small to be attractive to the weevil during the peak egg-laying period. Stem weevil damage in Crops seeded after this date generally is reduced to the point that it is unlikely that an insecticide treatment will be needed. Keep in mind, however, that sunflower yield and quality will be reduced significantly in Crops planted after June 15.
Sunflower stem weevil larvae in stalk.
Actual emergence dates are affected by weather and location and vary from early May to early June. Egg laying starts 10 to 14 days after emergence and can continue into early August. Larvae hatching from eggs laid later in the season have poor survival. The degree-day model has practical implications for stem weevil management. Begin scouting at sunflower growth stage V2-V4 and continue until early July.