Rice tolerance to acetochlor with a fenclorim seed treatment

Abstract

Rice producers in the U.S. need effective herbicides to control problematic weeds. Previous research has demonstrated that acetochlor can provide in-season weed control in rice; however, undesirable injury is common. Thus, trials were initiated in 2020 and 2021 to evaluate 1) rice cultivar tolerance to microencapsulated (ME) acetochlor with the use of a fenclorim seed treatment at 2.5 g ai kg-1 of seed, 2) a dose-response of a fenclorim seed treatment with ME acetochlor, and 3) rice tolerance to fenclorim and ME acetochlor under cool, wet conditions. For all trials, acetochlor was applied delayed-preemergence (4 to 7 days after planting). In the dose-response trials and in the presence of acetochlor, the fenclorim seed treatment rate of 2.5 g ai kg-1 reduced rice injury and increased rice plant heights and shoot numbers relative to acetochlor without fenclorim and was comparable to the nontreated control in all evaluations. In the cultivar screening, 14 of 16 cultivars exhibited < 20% injury with acetochlor at 1,260 g ai ha-1 and fenclorim at 2.5 g ai kg-1 2 weeks after emergence (WAE) at the Pine Tree Research Station (PTRS). At the Rice Research and Extension Center (RREC) 2 and 4 WAE and PTRS 4 WAE, all cultivars exhibited < 20% injury with acetochlor and fenclorim. The fenclorim seed treatment in the presence of acetochlor provided comparable rice plant height, shoot numbers, groundcover, and rough rice yield to the nontreated control. Under cool, wet conditions, rice injury without fenclorim ranged from 15 to 60% with acetochlor at 1,050 g ai ha-1, while injury from acetochlor with the fenclorim seed treatment ranged from 0 to 20%. Based on the results of these experiments, the fenclorim seed treatment appears to safen an assortment of rice cultivars from injury caused by ME acetochlor.

Weed control and rice response to microencapsulated acetochlor and a fenclorim seed treatment on a clay soil

“…The ability of fenclorim as a safener to reduce rice injury caused by acetochlor and pretilachlor has been well documented (Avent et al., 2023a, 2023b; Chen et al., 2013; Han & Hatzios, 1991; Quadranti & Ebner, 1983; Usui et al., 2001). Furthermore, at both evaluation timings, rice injury caused by acetochlor averaged ≤23% with the fenclorim seed treatment (Table 2).…”

“…As acetochlor rate increased, rice injury likewise increased at both evaluation timings (Table 2). Averaged over the fenclorim seed treatment, acetochlor at 1.1 and 1.7 lb ai acre −1 The ability of fenclorim as a safener to reduce rice injury caused by acetochlor and pretilachlor has been well documented (Avent et al, 2023a(Avent et al, , 2023bChen et al, 2013;Han & Hatzios, 1991;Quadranti & Ebner, 1983;Usui et al, 2001). Furthermore, at both evaluation timings, rice injury caused by acetochlor averaged ≤23% with the fenclorim seed treatment (Table 2).…”

“…Furthermore, the fenclorim seed treatment did not influence barnyardgrass control. On a silt loam soil, research has already demonstrated the ability of a fenclorim seed treatment to improve rice tolerance to acetochlor (Avent et al, 2023a(Avent et al, , 2023b. However, clay content negatively correlates with acetochlor activity (Reinhardt & Nel, 1990), and no literature has described how fenclorim behaves in clay soils.…”