Rice Cultivar Response to Florpyrauxifen-Benzyl When Applied with Imazethapyr and a Cytochrome P450 Inhibitor

Abstract

Understanding cultivar responses to a new herbicide is crucial to determining appropriate herbicide use and management practices. Florpyrauxifen-benzyl is a new rice herbicide developed to control troublesome weeds in rice production. Little research has been conducted to characterize rice cultivar responses to florpyrauxifen-benzyl, and thus, a field experiment was conducted at the Pine Tree Research Station (PTRS) in 2017 and 2018 and at the Rice Research and Extension Center (RREC) in 2018 to determine rice cultivar tolerance to florpyrauxifen-benzyl as influenced by herbicide rate, the addition of imazethapyr, and rice growth stage. Another experiment was conducted in 2018 at PTRS and RREC to assess crop response when florpyrauxifen-benzyl at different rates is applied with and without malathion, a known cytochrome P450 inhibitor. Three cultivars were evaluated in both experiments: a long-grain variety “CL111,” a medium-grain variety “CL272,” and a long-grain hybrid “CLXL745.” Injury in the first experiment was higher when florpyrauxifen-benzyl was applied at 60 g ae ha−1 than at the labeled rate of 30 g ha−1, with the most injury being 10% when averaged over growth stage at the time of application. Generally, applications made at the 3-leaf growth stage resulted in the most injury; however, this injury was at most 14%. Additionally, there was no reduction in grain yield for any cultivar, indicating florpyrauxifen-benzyl can be used safely in conjunction with imazethapyr in imidazolinone-resistant rice. In the second experiment, there was no more than 10% injury and no reduction in grain yield, with the addition of malathion not causing an increase in rice injury. Results from these experiments indicate florpyrauxifen-benzyl can be mixed with imazethapyr and the addition of malathion will not lead to increased risk for injury to rice.

Florpyrauxifen-Benzyl Selectivity to Rice

“…Regarding the effect of P450 inhibitors on rice response to FPB, our result is similar to those observed on field experiments carried out in Arkansas rice areas [36]; they reported 2% of rice injuries when they applied FPB (30 and 60 g ai ha −1 ) plus malathion (700 g ai ha −1 ), and there was no detected lasting adverse effects on yield. The label recommendation does not allow the use of malathion on tank-mix or seven days before FPB application [27].…”

“…Likewise, larger rice plants are able to metabolize and detoxify auxin herbicides. However, for instance, at 7 DAA, we observed more injuries at V 6 applications than V 2 , and these results also were observed in a medium-grain rice cultivar sprayed with FPB in field conditions, where greater injury (13%) has been reported for applications in 5-leaf rice than at 1-leaf (<3%) [36]. These results are more related to the uncontrolled conditions at the field than the size of the rice.…”

“…On the other hand, the effect of two P450 inhibitors may have a negative effect on growth and injury, but the doses are still over the commercially recommended; thus, it seems to not compromise the selectivity [27]. Contrary to Wright et al's [36] conclusion, which suggests that there is no dependency of P450 on the degradation of this herbicide in rice, we considered that there could be more interaction of FBP with P450 inhibitors in plants since there have been reported 356 CYP genes encoding P450 enzymes on rice [48]. Hence, the addition of two inhibitors, dietholate followed by PBO, may inhibit other CYP isoenzymes that malathion does not do.…”

“…For the 2019/2020 season, imazapic + imazapyr (24.5 and 73.5 g ai ha −1 ) was applied postemergence to keep the plots free of weeds. The addition of acetolactate synthase inhibitor has been reported to be safe to rice when applied in a tank mix or close to FPB application [36]. Florpyrauxifen-benzyl applications were performed for each stage of the application corresponding to each treatment.…”

“…Previous rice crop observations have described leaf malformations, stem curling, chlorosis, height, tiller number reduction, and shoot dry weight reduction as common symptomology of FPB in rice [35]. Recent research has investigated rice cultivar's response to FPB regarding the temperature surrounding spraying time, growth stage application, and tank-mix with imazethapyr and malathion [35,36]. However, the effect of planting time, growth, and quantifying the effect of inhibitors on the dose of FPB or genes expression related to metabolism or bio-activation have not been fully described.…”