Potato injury risk with reduced PPO inhibitor herbicide rates

Tuesday, July 27, 2021
2:25 PM - 2:45 PM

The ability to use the protoporphyrinogen oxidase (PPO) inhibitor herbicides fomesafen, flumioxazin and sulfentrazone in potato is limited regionally or by soil type largely because of crop injury noted in research in the 1990s. With that in mind, here we reversed the research question to ask not how much herbicide the crop could tolerate but instead ask how much is needed to maintain weed control. Studies were conducted at two locations: one on silt loam soil and one on coarse-textured loamy sand. Overall, three advancements were observed. First, soil type played a greater than anticipated role in PPO inhibitor herbicide injury risk as it relates to high precipitation events. For example, in 2020 at the silt loam location there were 5 precipitation events across the season that exceeded 2.5 cm, including one 6 days after treatment (DAT), and a seasonal total precipitation that was over 10 cm greater than the previous year. Despite excessive moisture and initial potato injury, by 29 DAT injury was less than 10% and marketable tuber yield was similar among treatments. In contrast, in 2020 at the loamy sand location there were 4 precipitation events across the season that exceeded 2.5 cm and potato injury was as much as 60%. Second, in 2020 we presume the high amount of injury from flumioxazin was largely caused by precipitation prior to herbicide application and not after, as has been considered the case in practice for years. Finally, this work documents the fine line between yield reduction presumably caused by reduced weed control and yield reduction assumed to be related to herbicide injury. And, this “sweet spot” may differ by soil type and environmental conditions, supporting the notion that custom-tailored weed management may become more necessary as high precipitation events become more common in Upper Midwest USA agriculture.
Extension, Production, and Management