Crop response, weed management systems, and tank mix partners with isoxaflutole in HPPD tolerant cotton
Over half of the nation’s cotton is planted in Texas with 1.6 million hectare residing in the High Plains region. Since 2011, glyphosate resistant Palmer amaranth has threatened cotton production and alternatives to glyphosate-based systems are needed. Integrating soil residual herbicides such as isoxaflutole into a weed management system is an effective strategy to control glyphosate resistant weeds before they emerge. BASF Corporation is developing p-hydroxyphenylpyruvate dioxygenase (HPPD) tolerant cotton, which will allow growers to use isoxaflutole, an HPPD inhibiting HRAC Group F2 herbicide, in future weed management programs. Field experiments were conducted at New Deal, Lubbock, and Halfway, Texas in 2019 and 2020 to determine HPPD-tolerant cotton response and efficacy with isoxaflutole applied preemergence (PRE) or early-postemergence (EPOST) as part of a weed management program. At New Deal, cotton response was greatest following the EPOST application, but never exceeded 10%. Cotton response was greatest following the PRE application at Lubbock in 2019, but never exceeded 14%. In 2020 at Lubbock, cotton was replanted due to severe weather. There was <1% cotton response following the PRE application and maximum cotton response observed was 9% following the EPOST and MPOST applications. Lint yields and fiber quality parameters were not different from the weed-free nontreated control. At 14 and 21 days after the preemergence treatment at Halfway, all treatments containing isoxaflutole controlled Palmer amaranth ≥94%. All treatments controlled Palmer amaranth ≥94% 21 days after the EPOST application. All systems that included isoxaflutole preemergence decreased Palmer amaranth density 96-99% while treatments with isoxaflutole applied early postemergence decreased Palmer amaranth density 88-94% when compared to the nontreated control 21 days after the EPOST application. Twenty-one days after the mid-postemergence treatment, systems with isoxaflutole in the early postemergence application controlled Palmer amaranth 88-93% while systems with isoxaflutole PRE controlled Palmer amaranth 94-98%. End of season weed control was lowest in the system without isoxaflutole (88%) and when isoxaflutole was used in the early postemergence application (88-91%). Another research project was developed in 2019 and 2020 to examine weed control following isoxaflutole applied preemergence alone and when used with a number of tank mix partners at their full and half labelled rates across the cotton belt. In 5 of 7 locations, Palmer amaranth was completely controlled at 14 days after application when isoxaflutole was mixed with the high rate of fluometuron, prometryn, and S-metolachlor. The addition of the high rate of diuron and fluridone provided the greatest control 42 days after application at 4 of 7 locations. At all three locations where large crabgrass was present, isoxaflutole plus the high rate of diuron provided the greatest control at 14 days after application. In 2 of 3 locations, isoxaflutole plus the high rate of pendimethalin and S-metolachlor improved large crabgrass control at 42 days after application when compared to isoxaflutole alone. At 14 and 21 days after application, morningglory control was ≥95% at all locations where this weed was present following isoxaflutole plus of the high rate of diuron and at 3 of 4 locations following isoxaflutole plus the high rate of fluometuron. At 42 days after application at all locations, isoxaflutole plus diuron and fluridone and isoxaflutole plus the high rate of fluometuron improved morningglory control compared to isoxaflutole alone.