Herbicide options for cultivated wild rice ( Zizania palustris ) in California

Wild rice is a high-value specialty crop in California. Weeds are an important pest issue in this crop, yet to date, only carfentrazone is registered for weed control. Herbicide field trials were conducted in 2022 and 2023 in Shasta and Yolo Counties, in support of the IR-4 project’s mission to register new pesticides for specialty crops. Herbicides tested for efficacy and crop safety included cyhalofop-butyl, florpyrauxifen-benzyl, penoxsulam, triclopyr, and propanil, at two application rates each, as well as carfentrazone applied at the labeled rate. At all sites, weed control was acceptable with most treatments and comparable to carfentrazone. Generally, florpyrauxifen-benzyl, penoxsulam, and triclopyr provided the greatest broad-spectrum weed control. In particular, uncommon weeds such as common spikerush and longleaf pondweed (Shasta County sites in 2022 and 2023, respectively) were controlled well with these herbicides. Propanil was also very effective against these two species, yet it only provided up to 25% control of ricefield bulrush. Crop response to herbicides was variable. Cyhalofop-butyl, florpyrauxifen-benzyl, propanil, and carfentrazone all caused minor and transient injury to the wild rice, characterized by chlorosis, leaf burn, and stunting. Florpyrauxifen-benzyl and triclopyr also caused some leaf deformation, which the wild rice did not recover from. The most significant crop injury was caused by penoxsulam, resulting in severe or complete stand loss at the low and high rates, respectively, across all site-years. Triclopyr also caused unacceptable lodging at both rates at all sites, significantly reducing yield at the higher rate. Crop yields in non-injured plots were similar to the untreated control and carfentrazone, although the higher rate of florpyrauxifen-benzyl did reduce yields somewhat. This data provides important crop-safety information for wild rice and will inform further herbicide program research toward potential registration for wild rice in California.