Influence of Herbicide Safeners On Creeping Bentgrass Herbicide Tolerance.

Creeping bentgrass (CBG) (Agrostis stolonifera) is the most widely used cool-season turfgrass species on golf course fairways and tees in the United States, but it is tolerant to few postemergence herbicides. Topramezone is a p-hydroxyphenylpyruvate dioxygenase-inhibiting herbicide recently registered for use in cool-season turfgrass and centipedegrass (Eremochloa ophiuroides); however, it is not labeled for use on CBG. Previous experiments demonstrated that the safener cloquintocet-mexyl applied at 185 g ha^-1 increased CBG tolerance to topramezone at 37 g ha^-1. Data describing CBG tolerance and weed control with topramezone and lower rates of cloquintocet-mexyl are warranted. Greenhouse experiments were conducted in 2012 at the University of Tennessee to evaluate CBG tolerance to topramezone applied with various rates of cloquintocet-mexyl. Topramezone (37 g ha^-1) was applied to mature ‘Penncross’ CBG alone or in combination with cloquintocet-mexyl at 185, 93, 37, 28, 19 or 9 g ha^-1. Treatments were in arranged in a completely randomized design with four replications and repeated in time. Injury was evaluated visually and using digital image analysis at 7, 14 and 21 days after treatment (DAT). Aboveground biomass was evaluated 21 DAT. Cloquintocet-mexyl applied at ≥ 28 g ha^-1 reduced CBG injury at 14 and 21 DAT in one experimental run. Cloquintocet-mexyl did not reduce control of large crabgrass (Digitaria sanguinalis), goosegrass (Eleusine indica) or common bermudagrass (Cynodon dactylon) in other greenhouse experiments. Future experiments will investigate mechanisms by which cloquintocet-mexyl increases CBG tolerance to topramezone and evaluate topramezone and cloquintocet-mexyl combinations in field experiments.