Evaluating the impact of planting date on Dectes stem borer infestations of South Dakota sunflowers

The Dectes stem borer, Dectes texanus LeConte (Coleoptera: Cerambycidae), is a common pest of sunflowers (Helianthus annuus L.) in South Dakota. There is no economic loss associated with the stalk boring activity of Dectes stem borer in sunflower. The economic losses due to this pest are associated with lodging resulting from larval girdling of the stalks prior to harvest. Although Dectes stem borer is a common pest of sunflowers, results from the National Sunflower Association’s biennial survey indicate that the presence of Dectes stem borer in South Dakota sunflowers has increased by approximately 28% during the last four years. In addition, the presence of abnormally large red sunflower seed weevil populations has led efforts to change cultural management practices and employ early planting dates to reduce red sunflower seed weevil damage. However, there is evidence from previous research in the southern US that early-planted sunflowers may be more likely to be infested by Dectes stem borer and have increased lodging. Therefore, the objective of this research was to determine if early planted sunflowers in South Dakota increase Dectes stem borer infestation and lodging. The field site was at the Dakota Lakes Research Farm near Pierre, SD. For both years 2023 and 2024, early planting was done in early May, and late planting was done in mid-June. Both the early and late-planted sunflower plots were evaluated for lodging and infestation. The results indicated much higher than expected infestation in both planting dates, with increased lodging present in the early-planted sunflower.