The Potential Interaction of Preventative Treatments for Insect and Weed Control

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 in use of pre-emergence herbicides to manage glyphosate resistant weeds. Field studies were conducted in 2013 and 2014 to determine the potential interaction between pre-emergence herbicides and neonicotinoid insecticides and their efficacy in control of thrips (Thysanoptera) 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 studies for both years, applications of pre-emergence herbicides increased thrips numbers and thrips injury ratings as well as reduced plant vigor and plant biomass. The tests also documented a failure of Cruiser (thiamethoxam) in controlling populations of thrips. 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.