Effect of Thiamethoxam on Early Growth of Soybeans Under Differing Water Regimes.

Thiamethoxam is a systemic insecticide that has been patented as promoting crop growth in the absence of pest pressure. In soybean production, thiamethoxam applied with a fungicide seed treatment has been suggested to increase early-season soybean growth and development. This response is speculated to be more evident under stressful conditions such as water deficit. Our objective was to evaluate the effect of thiamethoxam on soybean growth and development under differing degrees of water deficit. A greenhouse experiment was conducted three times in 2008. Treatments included an untreated control, mefanoxam + fludioxonil, and mefanoxam + fludioxonil + thiamethoxam. Cultivars Asgrow AG2802 and Stine S-2932-4 were utilized for this study. Pots were watered back to a specified target weight for one of three water regimes on a daily basis. Target weights for each water regime were a percentage of relative soil water content (RSWC), obtained by subtracting the weight of media at pot capacity from the 200 g of dry media added to each pot. Water regimes consisted of a well-watered control (75% RSWC), a moderate moisture stress (50% RSWC), and a severe moisture stress (25% RSWC). Sampling was conducted at the V1, V2, and V3 growth stages for biomass accumulation and leaf area. Root characteristics were examined using WinRhizo software (Reagent Instruments, Canada). The experimental design was a randomized complete block design in a split-plot arrangement with 4 replications. Whole plots were the water regimes while the split plots were the combination of treatment, variety, and sampling date. Data summarizing this experiment will be presented.