The Effects of Preharvest Glyphosate With Ammonium Adjuvants on Grain Protein Content of Hard Red Spring Wheat

Abstract

Laboratory and field experiments were conducted to investigate if glyphosate applied with ammonium fertilizers as adjuvant at or after physiological maturity (PM) would lead to an overestimation of grain protein content in hard red spring wheat (HRSW). In the laboratory experiment, grain was mixed with liquid and dry ammonium sulfate (AMS) or a urea ammonium nitrate (UAN) solution. A 15 lb N/acre and 148 lb N/acre equivalent of UAN led to an 11 and 42% overestimation of the grain protein content, confirming that adulteration of grain with ammonium fertilizers is possible. In the field experiment, treatments included an untreated control, water alone, a glyphosate solution, an AMS solution, a glyphosate solution with AMS, an UAN solution, and a glyphosate solution with UAN. The rates for glyphosate, liquid AMS, and liquid UAN were 0.77 lb acid equivalent/acre, 5.0 lb AMS/acre or 5% v/v, 5.3 lb UAN/acre or 5% v/v, respectively. The treatments were applied at PM, 5 days after PM, and 10 days after PM. Grains were harvested at 12 days after PM and grain protein content was determined immediately and 7 days after harvest. None of the glyphosate, AMS, and UAN combinations applied at the labeled rates at or post PM caused an overestimation of grain protein content. This means that it is highly unlikely that grain protein content in HRSW can be adulterated with an preharvest glyphosate application.