Urea ammonium nitrate as the carrier for preplant burndown herbicides

Abstract

AbstractPreplant weed control is a common practice for many small grain farmers. The timing of these applications often coincides with starter nitrogen (N) fertilizer application. Co‐application of the herbicides and N fertilizers, such as urea‐ammonium nitrate (UAN), can reduce the number of trips across the field, labor costs, and the costs of N and herbicide applications. However, there is a dearth of information on the effect of herbicide‐N fertilizer mixtures on herbicide efficacy. Field studies were conducted in the summer of 2021 and 2022 to evaluate the effect of UAN (32‐0‐0) rate (0%, 25%, 50%, 75%, and 100% of carrier volume) on the efficacy of three non‐selective herbicides (glyphosate [1260 g ae ha−1], paraquat [560 g ai ha−1], and tiafenacil [74 g ai ha−1]). There was no effect of UAN volume on herbicide efficacy. The addition of UAN did not reduce the efficacy of glyphosate, paraquat, or tiafenacil. At 3 weeks after herbicide application, glyphosate efficacy ranged from 92% to 94% (broadleaved weeds) and 97% (grassy weeds). Paraquat efficacy ranged from 63% to 87% (broadleaved weeds) and 87% (grassy weeds). Tiafenacil efficacy ranged from 52% to 74% (broadleaved weeds) and 70% (grassy weeds). Higher application volume may be needed to increase the efficacy of contact herbicides such as paraquat and tiafenacil.