Influence of simulated rain timing and flumioxazin rate on Covington sweetpotato yield and quality

Abstract Flumioxazin is a preemergence herbicide that is widely used pretransplant on conventional sweetpotato hectarage as part of weed management programs in North Carolina; despite this, some growers have concerns that flumioxazin may be injurious to sweetpotato, even at recommended rates if rain falls near application. Thus, field studies were conducted in 2021 and 2022 in Clinton, North Carolina, to evaluate the performance of flumioxazin under several simulated rain conditions. Studies evaluated a complete factorial arrangement of treatments with three flumioxazin rates and three simulated rain treatments. Herbicide treatments included no herbicide, and two rates of flumioxazin (107 g ai ha −1 and 214 g ai ha −1 ). Irrigation treatments included 1.9 cm of simulated rain applied before flumioxazin, 1.9 cm applied after flumioxazin, and no simulated rain. No visual injury from herbicide or rain treatments was observed. Yields of No. 1 and marketable sweetpotatoes were reduced by 25% and 14%, and total yield was reduced by 11% when the higher rate flumioxazin (214 g ha −1 ) was applied compared to the no-herbicide treatment. However, the lower (registered) rate of flumioxazin (107 g ha −1 ) did not lead to a reduction in yield compared with yield from the no-herbicide treatment. No interactions between irrigation timing and herbicide were observed, and irrigation timing alone did not affect sweetpotato yield. Average length-width ratio (LWR) was calculated for No. 1 sweetpotato storage roots as a metric of root shape. In 2021, herbicide did not affect LWR. In 2022, compared with the no-herbicide treatment, the LWR of No. 1 sweetpotato was smaller after the higher rate of flumioxazin (214 g ha −1 ) was applied compared with LHR of the no-herbicide treatment, resulting in rounder sweetpotato roots. Flumioxazin applied at 107 g ha −1 did not reduce LWR compared with the no-herbicide treatment. The results of this study highlight both the safety of flumioxazin when applied at registered rates and the importance of appropriate application procedures to prevent overapplication.