Bispyribac is registered for postemergence control of broadleaf, sedge, and grass weeds in rice. Bispyribac inhibits the acetolactate synthase enzyme in sensitive plants. Herbicides in this class of chemistry require a spray adjuvant to achieve optimal efficacy, often achieve different levels of weed control according to the spray adjuvant used, and typically have rainfast periods of at least 6 to 8 h. Efficacy and rainfastness of bispyribac can be affected by spray adjuvant and the addition of urea ammonium nitrate (UAN). Greenhouse experiments were conducted to investigate the effect of spray adjuvant type, addition of UAN, and soil moisture on bispyribac efficacy on barnyardgrass. Control of barnyardgrass was improved when UAN was added to bispyribac at 0.4 or 0.8 g ha−1 plus an organosilicone-based nonionic surfactant (OSL/NIS) or methylated seed oil/organosilicone (MSO/OSL) spray adjuvant. The type of adjuvant added to the spray solution affected bispyribac efficacy on barnyardgrass. The addition of UAN decreased the rainfast period from 8 h (registered rainfast period) to 1 or 4 h (99 to 100% control) when either the OSL/NIS or MSO/OSL adjuvant was applied with bispyribac, respectively. Applying UAN and OSL/NIS or MSO/OSL adjuvant with bispyribac enhanced efficacy and reduced the time period required between bispyribac application and washoff during a rainfall event. Increasing soil moisture conditions resulted in greater efficacy from bispyribac when applied with and without UAN.

Greenhouse experiments were conducted in the summer of 2002 to determine the effect of root-knot nematodes on purple nutsedge suppression and chile pepper response after applications of halosulfuron. Purple nutsedge and chile pepper plants were grown together in 20-cm-diam pots, inoculated with root-knot nematodes, and treated with halosulfuron 2 or 4 wk after inoculation. Root-knot nematode infection had no effect on purple nutsedge control or chile pepper injury after treatment with halosulfuron, regardless of application timing. However, root-knot nematode reproduction was lower in pots that received a halosulfuron treatment, particularly halosulfuron applied 2 wk after inoculation. Controlling purple nutsedge using halosulfuron in a field infested with root-knot nematodes could also decrease the amount of nematode inoculum that is available for infecting chile plants later in the season.

Field research was conducted in southern New Mexico to determine the effect of halosulfuron rate, timing of application, and adjuvant on purple nutsedge suppression and chile pepper injury under cultivated conditions. POST-directed treatments of 36 or 53 g ai/ha were applied 2 or 4 wk after thinning direct-seeded chile pepper. Herbicide treatments included a nonionic surfactant or methylated seed oil plus ammonium sulfate plus polyacrylamide polymer. Herbicide rate, adjuvant, and timing of the application had little effect on overall nutsedge suppression; however, herbicide treatment proved to be an important component for managing purple nutsedge in this experiment. Yields were higher with halosulfuron treatment compared with the weedy control. Whereas halosulfuron treatment with 53 g/ha increased chile yield relative to the weedy control, injury and yield results comparing 36 and 53 g/ha rates consistently suggested that halosulfuron should be applied at rates ≤ 36 g/ha in a single application to avoid possible injury. Halosulfuron treatment combined with cultivation and effective crop rotation may reduce the impact of purple nutsedge interference in chile pepper.