Effect of fall-applied residual herbicide mixtures on rice growth and yield

The recommended method of control for glyphosate-resistant (GR) Italian ryegrass in Mississippi is the utilization of fall-applied residual herbicides; however, these treatments may negatively impact rice performance. A field study was conducted at the Mississippi State University Delta Research and Extension Center to evaluate rice performance following fall-applied treatments of residual herbicides plus flumioxazin at different rates. Pooled over with and without flumioxazin and herbicide rates, clomazone and dimethenamid-P caused < 10% injury 28 d after emergence (DAE). Acetochlor delayed rice maturity 2 d when compared to clomazone, dimethenamid-P, and flumioxazin. Rice density was reduced ≥ 4 plants m -2 following fall-applied acetochlor and dimethenamid-P compared to the nontreated. Rough rice yields were reduced ≥ 670 kg ha -1 with fall-applied acetochlor alone and dimethenamid-P compared to the nontreated. Acetochlor should not be utilized as a fall-applied treatment in areas scheduled for growing rice the following season. Given current label restrictions and rice injury caused by acetochlor and dimethenamid-P, clomazone remains the only viable option for controlling GR Italian ryegrass where rice is scheduled to be planted the following spring.