Postemergence-directed applications of pendimethalin for control of early-season weeds in chile pepper

In New Mexico chile pepper production, pendimethalin is traditionally applied shortly after crop thinning, which is 9 to 10 wk after crop seeding. Pendimethalin applications before crop thinning may be a method for controlling early-season weeds in chile pepper; however, chile pepper tolerance to early-season applications of pendimethalin is poorly understood. We conducted a greenhouse study to evaluate young chile pepper responses to pendimethalin. We also conducted a field study to determine weed and chile pepper responses to early-season, postemergence-directed (POST-directed) pendimethalin in combination with herbicides registered for preemergence (PRE) applications. The greenhouse study included three treatments administered when chile pepper was at the 4-leaf stage: 1) pendimethalin applied to foliage and soil, 2) pendimethalin applied soil only, and 3) a non-treated control. The field study included four treatments: 1) PRE applications of napropamide followed by POST-directed pendimethalin at 5 wk after crop seeding, 2) PRE applications of clomazone followed by POST-directed pendimethalin at 5 wk after crop seeding, 3) POST-directed pendimethalin without PRE herbicides, and 4) non-treated, weed-free control. We conducted the field study at two sites that differed in soil texture. Pendimethalin application rates were maximum labelled rates for the specific soil. Results from the greenhouse study indicated that pendimethalin applied to foliage and soil stunted two of five cultivars, whereas pendimethalin applied to soil did not affect chile pepper height, fresh weight, dry weight, and root area. Results from the field study indicated POST-directed pendimethalin did not affect chile pepper height or fruit yield, or cause visual symptoms of herbicide injury. POST-directed pendimethalin reduced the densities of weeds, including junglerice. The results of this study indicate that POST-directed applications of pendimethalin at 5 wk after crop seeding do not cause crop injury or yield loss, while providing some weed control benefits, in chile pepper.