Early planting and early maturing sunflower hybrids are neglected management tools to remedy outbreaks of the red sunflower seed weevil (Coleoptera: Curculionidae)

Abstract The red sunflower seed weevil, Smicronyx fulvus L. (Coleoptera: Curculionidae), is a univoltine seed-feeding pest of sunflowers. Recent increases in S. fulvus damage and resistance to pyrethroids show a need for additional tools to complement insecticides. Cultural practices to advance sunflower bloom before S. fulvus emergence is complete were shown to be effective in the 1980s, but are not in use today. To address growers’ concerns, insecticide-free field trials were conducted to assess the efficacy, profitability, and sustainability of S. fulvus avoidance with early planting and early maturing hybrids. In central and western South Dakota, May plantings reduced S. fulvus damage by 60% or more relative to typical plantings from 15 to 20 June, and an early maturing hybrid may further reduce seed damage. However, in North Dakota, early planting did not provide a clear advantage, likely because of relatively low S. fulvus populations. Yields generally showed no negative effect from planting early, but yields were lower for the most common planting period (15–20 June) in central South Dakota. Adult S. fulvus emerged earlier where early planted sunflowers were grown in the previous year, but the benefits of weevil avoidance were not eliminated. The strategy of S. fulvus avoidance through early planting (before ≈ 15 May) and early maturing hybrids seems justified in South Dakota where pest populations are very high and insecticide efficacy is low because of resistance to pyrethroid active ingredients. For other key sunflower-growing areas including North Dakota, avoidance may become useful in the future if S. fulvus populations increase.