Tolerance of Kentucky Bluegrass Cultivars to Sulfosulfuron.

Sulfosulfuron [1-(4,6-dimethoxypyrimidin-2-yl)-3-[(2-ethanesulfonyl-imidazo[1,2-a]pyridine-3-yr)sulfonylurea] is a sulfonylurea herbicide that is labeled for use in cool-season and warm-season turfgrass species.  This herbicide controls susceptible weed species by inhibiting the production of three essential amino acids used in protein biosynthesis.  Sulfosulfuron is effective in controlling many of the broadleaf weeds found in turfgrass environments.  Limited information is available on the tolerance of Kentucky bluegrass cultivars to sulfosulfuron.  Our objective was to identify the response of various Kentucky bluegrass cultivars to sulfosulfuron. The National Turfgrass Evaluation Program trial at the University of Massachusetts Amherst was used to evaluate the herbicide tolerance of 172 cultivars of Kentucky bluegrass.  These plots were established in 2000, and maintained with 196 kg N ha^-1 yr^-1. Plots were 0.9 by 1.8 m in size.  This trial was a split-block design with three blocks having cultivars as the main plot and two mowing heights (1.25 and 3.125 cm) as sub-plot.  Experimental area was mown twice a week with clippings returned.  Sulfosulfuron was applied POST to Kentucky bluegrass at the rate of 75 g ai/ha on July 21, 2009.  Treatments were applied using a CO₂-backpack sprayer with Teejet XR 1104 VS nozzles at 152 kPa using a spray volume of 467 L/ha.  Turfgrass injury was visually estimated on a scale of 1 to 9, 1 = dead turfgrass, while 9 = healthy green turfgrass. Injury ratings were made 1, 2, and 3 weeks after treatment (WAT). Little or no injury observed on 1.25 cm height of cut, therefore injury data are reported for 3.125 cm height of cut only. In general, Kentucky bluegrass exhibited a wide range of tolerance to sulfosulfuron. Injury was significantly greater at 2WAT, but no interaction was observed between cultivar and injury rating period. ‘Serene’ and ‘Langara’ Kentucky bluegrass exhibited little injury following sulfosulfuron treatments at 1 WAT and injury was statistically equal to the untreated check. Injury ratings ranged from 4.67 (‘Champagne’ and ‘Misty’) to 8.67 (‘Serene’) at 1 WAT.  Injury following sulfosulfuron was significantly greater at 2 WAT.  ‘Serene’ was the only entry to provide an injury rating greater than 8.0, which was equal to the untreated check.  Injury ratings ranged from 4.0 (‘Champagne’) to 8.67 (’Serene’) at 2 WAT.