Discovery of Accase Herbicide Resistance in Bermudagrass.

Common bermudagrass (Cynodon dactylon) is well known to turfgrass managers as a weed in improved varieties of bermudagrass turf.  Common bermudagrass can infest an area and cause detrimental performance and playability of a turfgrass stand, whether that be on a golf course or sports field.  ACCase is a key enzyme that catalyzes the formation of malonyl CoA from the carboxylation of acetyl CoA, involved in fatty acid biosynthesis in grasses.  ACCase herbicides disrupt this enzyme causing plant injury or death.  A herbicide resistance cultivar that would allow turfgrass managers to remove common bermudagrass without glyphosate or sod-cutting would be a valuable tool.  Therefore, a spray chamber and greenhouse experiment was conducted to study the sethoxydim resistance level of an experimental bermudagrass line (93-175) that was found with minimal injury after two applications of sethoxydim at a rate of 280g ai/ha in the field.  Ten rates of sethoxydim ranging from zero to 800 grams of sethoxydim per hectare were evaluated in a randomized complete block with four replications.  Resistance was assessed with visual ratings of percent injury 28 days following treatments.  ‘Tifway’, a non-sethoxydim resistant cultivar exhibited 45 percent injury at 300g ai/ha, 97 percent injury at 400g ai/ha, and 94 percent injury at 800g ai/ha.  When 93-175 was sprayed at the same rates, percent injuries were 4, 16, and 15 respectively.  More comprehensive spray chamber and field experiments will be performed using sethoxydim, clethodim, and fluazifop to determine whether or not 93-175 has resistance to other ACCase inhibiting herbicides.  Higher herbicide concentrations will also be applied to discover the rates which confer 50 percent injury for 93-175.