The effect of pre-emergence herbicides on neonicotinoid seed treatments in seedling cotton
Dr. Scott D. Stewart
Dr. Larry Steckel
Dr. Heather Marie Kelly
University of Tennessee
There is a growing concern about the effectiveness of neonicotinoid seed treatments against thrips (Thysanoptera) populations in seedling cotton (Gossypium hirsutum). This concern coincides with an increase use of pre-emergence herbicides to manage glyphosate resistant weeds. Field and greenhouse studies were conducted in 2013 to determine how pre-emergence herbicides impact the control of thrips with neonicotinoid insecticides in cotton. Different pre-emergence herbicide treatments were applied to planted cotton seed treated with the neonicotinoid insecticides Cruiser (thiamethoxam, Syngenta) or Gaucho (imidacloprid, Bayer CropScience). In the field study, pre-emergence herbicides increased thrips numbers and injury ratings and reduced vigor and plant biomass. The test also documented a failure of Cruiser (thiamethoxam) in controlling populations of thrips. Leaf samples of seedling cotton from the field study and greenhouse study were sent to the USDA AMS National Science Laboratory in Gastonia, NC for analytical testing of neonicotinoid concentrations. Although pre-emergence herbicides appeared to increase thrips injury and negatively affect plant growth, neonicotinoid concentrations in leaf tissue were similar or higher where herbicides were applied.
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