Golf Course Management

DEC 2012

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research Area under the disease progress curve (AUDPC) was calculated. The date of initial disease obser- vation was also recorded and analyzed to assess treatment impact on disease incidence. After each fungicide application and during each disease severity rating, turfgrass quality was assessed visu- ally and rated on a scale of 1-9, where 9 is best, 5 is minimally acceptable and 1 is bare ground. Data were analyzed to determine treatment effects among and within trial years. Experiment 1: Optimal application rate and timing A three-year field experiment (experiment 1) was initiated in 2007 to determine the optimal rate and soil temperature-based timing of triad- imefon (Bayleton 50DF, Bayer) and tebucon- azole applications for fairy ring prevention. (Edi- tor's note: The tebuconazole product tested was a previous experimental formulation that was not released.) Plots were 5 feet × 10 feet (1.5 meters × 3 meters), with treatments replicated four times in a split-block randomized complete block design with application timing as the main plot and fun- gicide as the subplot. Plots were not re-random- ized between trial years in an effort to assess the multiyear impact of the treatments. Treatments were initiated in the spring from early March to late May when five-day average soil temperatures reached 50 F, 55 F, 60 F, 65 F, 70 F or 75 F (10 C, 13 C, 16 C, 18 C, 21 C or 23 C). Soil temperatures were collected daily with a Watchdog data logger (Spectrum Technologies) with an external soil probe located 2 inches (5 centimeters) below the soil surface. Fungicide treatments included a low and a powered boom sprayer at 40 psi (276 kPa) using flat-fan nozzles calibrated to deliver water at 2 gallons/1,000 square feet (81.5 milliliters/square meter). No wetting agents were tank-mixed with these applications, but the soil surfactant Cascade Plus (Precision Laboratories) was applied sepa- rately at 4 fluid ounces/1,000 square feet (1.27 milliliters/square meter) every 28 days to reduce localized dry spot. high product rate of Bayleton 50DF (1 ounce or 2 ounces/1,000 square feet [0.15 or 0.30 gram a.i./square meter]) and tebuconazole (0.26 ounce or 0.49 ounce a.i./1,000 square feet [0.08 or 0.15 gram a.i./square meter]) and an untreated control. Treatments were applied with a CO2 - Experiment 2: irrigation timing and fungicide + surfactant tank mixtures A two-year field experiment (experiment 2) was initiated in 2008 to examine the impact of irrigation timing and fungicide + surfactant tank 76 GCM December 2012 mixtures on the performance of preventive DMI applications. Plots were 5 feet × 10 feet, with treat- ments replicated four times in a split-block ran- domized complete block design with fungicide as the main plot and irrigation timing and surfac- tant tank mix as subplots. Plots were not re-ran- domized between trial years in an effort to assess the multiyear impact of the treatments. Fungicide treatments included two applica- tions of a low rate of triadimefon (Bayleton FLO at 1 fluid ounce/1,000 square feet [0.15 gram a.i./ square meter]) and triticonazole (Triton 70WG at 0.25 ounce/1,000 square feet [0.08 gram a.i./ square meter]) and an untreated control. Fungi- cides were applied as described previously with or without the surfactant Revolution (Aquatrols) at a rate of 6.0 fluid ounces/1,000 square feet (1.86 milliliters/square meter). No additional surfac- tants were applied to these plots during the exper- iment. Irrigation timing treatments included hand watering with 0.25 inch (6.4 millimeters) of irrigation either immediately or 10 hours after fungicide application. Treatments were applied on March 28 and April 25, 2008, and March 31 and April 28, 2009. The five-day average soil temperature at 2 inches (5 centimeters) on the first application date of both years was 55 F-60 F (13 C-16 C). Results In 2007, type I and II symptoms were first observed in late May just before the 75 F (23 C) application, making this a curative treatment in eight of the 20 total plots. Type II fairy ring symp- toms developed in the experimental areas in mid- June 2008 and mid-July 2009, and were not pres- ent in the experimental area during the treatment periods. In both field experiments, disease severity decreased over the years of the study. In experi- ment 1, AUDPC values were equivalent in 2007 and 2008 and significantly decreased in 2009. In experiment 2, AUDPC values also significantly decreased in 2009. Grayish brown turf discoloration was observed in plots treated with Bayleton 50DF or Bayleton FLO in late May 2008, resulting in a decrease in overall turf quality compared with plots treated with tebuconazole or Triton. This effect was more pronounced in plots treated twice with Bayleton FLO + Revolution than in plots treated with Bay- leton FLO alone. All Bayleton-treated plots recov- ered by mid-June, and overall turf quality ratings did not fall below acceptable levels (<5). Field experiment 1: application rate and timing Plots treated with both rates of tebuconazole

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