|BREDESON, MICHAEL - South Dakota State University|
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2015
Publication Date: 11/1/2015
Citation: Bredeson, M.M., Lundgren, J.G. 2015. Thiamethoxam seed treatments hav no impact on pest numbers or yield in cultivated sunflowers. Journal of Economic Entomology. 108(6):2665-2671. doi: 10.1093/jee/tov249.
Interpretive Summary: Neonicotinoid seed treatments are a widely used group of insecticides in many row cropping systems in the U.S. Nearly all sunflower seeds are treated with the seed treatment thiamethoxam, which is taken up by the developing plant. We tested whether thiamethoxam seed treatments reduce pests and improve yields, and also tracked how long thiamethoxam and its metabolite clothianidin are present in the plants under field conditions. Thiamethoxam seed treatments did not reduce plant-damaging pests at any of the experimental sites. This insecticide also did not improve yields. We found that thiamethoxam and clothianidin concentrations in the sunflower leaves diminished as the season progressed, and these chemicals were detectable through the bud stage and throughout flowering, respectively. This research suggests that when intense pest pressures are absent, neonicotinoid seed treatments in sunflowers may not consistently improve yields or reduce pests. Regulators, other scientists and extension personnel can use these results to develop recommendations for use of insecticidal seed treatments.
Technical Abstract: The use of neonicotinoid seed treatments is a nearly ubiquitous practice in sunflower (Helianthus annuus) pest management. Sunflowers have a speciose pest complex, but also harbor a diverse and abundant community of beneficial, non-target organisms which may be negatively affected by pest management practices. Here, we investigate how the foliar and subterranean arthropod pest communities in sunflower fields were affected by a thiamethoxam seed treatment over three site years. Thiamethoxam and its metabolite clothianidin in leaf tissue were quantified throughout the growing season, and yields were measured. Across site years, foliar herbivores and key pests of sunflowers were unaffected by the seed treatment. Likewise, subterranean herbivores were unaffected. Thiamethoxam was measurable in leaf tissue through the R1 plant stage, while its metabolite clothianidin was detected throughout flowering (R6). No difference in sunflower yield was observed between treatments across site years. This research suggests that when intense pest pressures are absent, neonicotinoid seed treatments in sunflowers provide few benefits to farmers in the form of pest reductions or yield improvements.