Golf Course Management

OCT 2013

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

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research Adding a plant growth regulator Trinexapac-ethyl is a foliarly absorbed plant growth regulator commonly used in turfgrass management. Greenhouse results indicate trinexapacethyl improves canopy color and reduces vertical shoot growth of both cool- and warm-season turfgrass species for weeks (14). Likewise, trinexapacethyl has been shown to positively infuence freezing tolerance of cool-season turfgrasses (8,10). Repeated trinexapac-ethyl applications to hybrid bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy] have also decreased nutrient concentration in leaves while increasing nutrient concentrations in rhizomes by 8% to 36%, resulting in a net increase in bermudagrass nutrient retention (7). Similar trinexapacethyl-induced reduction in nitrogen requirements has been reported for creeping bentgrass putting greens (4). The objective of this study was to determine how timing of fall applications of trinexapac-ethyl and/or nitrogen infuence subsequent growth, nitrogen status and spring canopy density of creeping bentgrass/annual bluegrass (Poa annua L.) putting greens. Materials and methods Studies were initiated in September 2009 and 2010 at the Pennsylvania State University Valentine Turfgrass Research Center (University Park, Pa.). The site was a mature, push-up putting green with a 3-inch (7.6-centimeter) sand cap overlying a Hagerstown silt loam. Year 1 Maintenance and fertilization. The Penn G-2 creeping bentgrass and annual bluegrass putting green was irrigated to prevent wilt. Throughout the 2009 season, the green was mowed six days/ week at a height of 0.126 inch (3.2 millimeters) and clippings were removed. In early September, granular urea, potassium sulfate and magnesium sulfate fertilizers were applied to deliver nitrogen, potassium, sulfur and magnesium at rates of 0.57, 2.56, 1.35 and 0.23 pounds/1,000 square feet (2.78, 12.49, 6.59 or 1.12 grams/square meter), respectively. Leaf clippings were collected Sept. 28 and analyzed. Following clipping collection, soil was randomly sampled to a depth of 4 inches (10 centimeters) and analyzed. Design and treatments. The experimental design was a randomized complete block with 72 plots (3 feet × 6 feet [0.9 meter × 1.8 meters]). On Sept. 30, 2009, three treatments were applied to each of the six blocks. A CO2-pressurized, single-nozzle (Tee-Jet TP11008E) wand-sprayer was used to apply soluble nitrogen (1:1 urea– N:NH4NO3 –N) at 0.61 pound/1,000 square feet (2.97 grams/square meter) in a tank-combination with Primo Maxx (trinexapac-ethyl, Syngenta) plant growth regulator at 0, 0.1, or 0.2 fuid ounce/1,000 square feet (0, 0.31, or 0.63 liters/ hectare). Plots initially treated with Primo Maxx at the 0.1 fuid ounce/1,000 square feet rate were re-treated with an equal application of Primo Maxx eight days later. Thus, all plots treated with Primo Maxx received a total of 0.2 fuid ounce of Primo Maxx/1,000 square feet in either a full- or split-application regimen. This procedure was repeated on randomly selected plots remaining within each block on Oct. 10, Oct. 21 and Nov. 1, 2009. These four initiation dates, each 10±1 days apart and centered on Oct. 15 (the 30-year average date of frst frost in University Park, Pa.), are the four experimental timing levels. Fall clipping yield. Measures of turfgrass growth and vigor were frst collected from treated plots on Oct. 9, and repeated every 10±1 days through Nov. 12, 2009. Thus, fall clipping yield data represent a single collection from plots treated Nov. 1 and cumulative collections from plots treated earlier. Clippings were immediately oven-dried, cooled in a desiccator and weighed. Mowing was discontinued in late November 2009, and plots were left uncovered over the winter. Grass clippings were collected in fall 2009 and 2010, and spring 2010 and 2011 to measure clipping yield, an indicator of turfgrass growth and vigor. Photo by Derek Pruyne October 2013 GCM 83

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