Golf Course Management

MAY 2019

Golf Course Management magazine is dedicated to advancing the golf course superintendent profession and helping GCSAA members achieve career success.

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05.19 GOLF COURSE MANAGEMENT 63 house culture at the University of Tennessee, Knoxville, Tenn. Seed was collected from all harvested plants and bulked by location. Emergence and seedling vigor experiment Harvested seed was planted and main - tained in a glasshouse under environmen- tal conditions designed for annual bluegrass growth. Plants were allowed to grow until Sept. 7, 2018, when seedling height was re - corded to determine seedling vigor. Resistance to non-selective herbicides After height data were collected, all trays were trimmed to a uniform height of 2 inches (5 centimeters) and supplied nutrients with a complete fertilizer. After a minimum of 17 days, plants were exposed to glyphosate (Roundup Pro, Monsanto) at 32 fluid ounces/ acre (1,120 grams/hectare), glufosinate (Finale, Bayer Environmental Sciences) at 6 quarts/ acre (1,680 grams/hectare), or diquat (Reward, Syngenta Professional Products) at 2 quarts/ acre (560 grams/hectare). These herbicides represented three distinct modes of action used for post-emergence annual bluegrass control in dormant warm-season turf: WSSA groups 9 (glyphosate), 10 (glufosinate) and 22 (diquat). Annual bluegrass biotypes were grouped into three categories based on percent survival data: suspected resistant (>30% survival), seg - regating for resistance (5% to 30% survival) and susceptible (<5% survival). These group - ings are similar to those used in a benchmark survey of herbicide resistance in annual rye - grass (Lolium rigidum) populations (1). What has been learned Plant collection Annual bluegrass was present above our benchmark sampling density at 87% of the golf courses surveyed. Of the 12 courses below our threshold, 10 were located in East Tennes - see. A low percentage of superintendents in- dicated they had changed their annual blue- grass management program on fairways and roughs from the previous year: 30% in East Tennessee, 29% in Middle Tennessee and 21% in West Tennessee. The large number of golf courses with annual bluegrass above the benchmark sampling density and the lack of diversity in control programs from year to year validated the rationale of our herbicide-resis - tant screening. Emergence and seedling vigor Annual bluegrass emergence varied accord - ing to golf course type, with biotypes from public golf courses emerging in an average of 6.3 days, compared with 8.1 days for bio - types collected from private golf courses. An- nual bluegrass seedling vigor varied by region, with biotypes from East and Middle Tennes - Poa annua plants collected in the field were transferred to the greenhouse and grown for seed that would, in turn, be used to grow larger populations to be used for research. Photo by José Javier Vargas Surveyors sampled Poa annua plants from a randomly selected golf hole at each golf course in the survey. Only 12 golf courses (13%) were eliminated from the study because their Poa annua populations were below the benchmark sampling density. Photo by James Brosnan

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