Creeping bentgrass (CBG) (Agrostis stolonifera L.) is the most widely used cool-season turfgrass species on golf course fairways and tees in the United States. However, CBG is tolerant of few postemergence herbicides. Preliminary research indicates CBG has tolerance to the HPPD-inhibiting herbicide topramezone, but improved tolerance is desirable. Two experiments were conducted at the University of Tennessee (Knoxville, TN) to evaluate safeners as a means to enhance CBG tolerance to the HPPD-inhibiting herbicide topramezone.

 

In Experiment 1, topramezone (37 g ha^-1) was applied alone or in combination with the herbicide safeners naphthalic anhydride (NA) and isoxadifen-ethyl (isoxadifen). Safeners were applied on the day of herbicide application or 3 days prior to herbicide application in a 5:1 or 10:1 safener:herbicide ratio. All treatments were applied with NIS at 0.25% v/v.  Treatments were applied with a water carrier at 221 L ha^-1 using a spray chamber to mature CBG grown in 6 cm cone-tainers filled with a peat moss, perlite, and vermiculite growing medium. Plants were maintained in a greenhouse under ambient light. Treatments for experimental runs A and B were applied on February 10 and June 1, 2012, respectively. Treatments were evaluated visually on a 0 (no injury) to 100% (complete control) scale at 7, 14 and 21 days after treatment (DAT). Plant were clipped to a 1.25 cm height at 21 DAT, verdure was collected, dried and weighed to quantify biomass production. Data were analyzed in a completely randomized factorial design with three replications in SAS 9.3 (α ≤ 0.05).

 

Application of NA and isoxadifen reduced injury from topramezone 14 DAT. Neither safener application timing nor safener rate were significant in either run. Therefore, it was determined that the lowest safener rate (5:1 safener:herbicide) applied at the time of herbicide application would be used in Experiment 2.

 

In Experiment 2, using the same methodology as experiment 1, benoxacor, cloquinctocet-mexyl, fenchlorazole-ethyl, isoxadifen-ethyl, NA, and mefenpyr-diethyl were investigated to determine their ability to reduce CBG injury from topramezone at 37 g ha^-1. Safeners were selected based on their commercial availability. The objective of this experiment was to identify optimal herbicide-safener pairings for candidate herbicides identified in Experiment 1.

 

In Experiment 2, application of topramezone alone at 14 DAT injured CBG 23%; injury was reduced to 12% when topramezone was applied with cloquintocet-mexyl. No other safener reduced CBG injury from topramezone. Further investigation of cloquintocet-mexyl in greenhouse and field trials to determine its ability to reduce CBG injury using lower safener rates and impacts on weed control is underway.