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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68 GOLF COURSE MANAGEMENT 05.19 tified the effects of a two-week application in- terval compared to a three-week application interval. e two-year field trial began Sept. 29, 2016, and final data collection for the first year was April 30, 2017. e second-year trial replication began Sept. 28, 2017, on a new area of the same green, and concluded April 30, 2018. is trial was subjected to replicated golfer traffic (76 golf rounds a day) to mimic real-world conditions and allow for a better as - sessment of the impact of the treatments on turfgrass recovery from traffic and on overall turfgrass quality. Preliminary observations for both years suggest that more frequent applications (every two weeks compared to every three weeks) will provide a greater expectation of disease inhibi - tion (Figure 1). Some abiotic damage has been observed in the coldest parts of the winter on plots that received Civitas Turf Defense when annual bluegrass was not actively growing. As a result, the highest turfgrass quality ratings were given to treatments that avoided applica - tions entirely or reduced application frequency of the horticulture oil in the winter months. Experiment 2: Iron sulfate rates and phosphorous acid e second trial explored different rates of iron sulfate in combination with a phospho - rous acid on a two-week application interval. is two-year field trial began Sept. 29, 2016, and final data collection for year 1 was taken April 30, 2017. e second-year trial replica - tion began Sept. 28, 2017, on a new area of the same green and concluded April 30, 2018. is trial was subjected to replicated golfer traffic (76 golf rounds a day) that mimicked real-world conditions and allowed for a better assessment of the impact of the treatments on turfgrass recovery from traffic and on overall turfgrass quality. e first- and second-year observations support earlier evidence that, as rates of iron sulfate increase, the inhibition of Microdo - chium patch also tends to increase (Figure 2). Higher rates of iron sulfate also tend to lead to greater turfgrass thinning and lower turfgrass quality ratings (especially at the highest rate of 2.0 pounds FeSO 4 /1,000 square feet [97.6 ki- lograms/hectare] every two weeks). Both years of preliminary data suggest that the addition of phosphorous acid with lower rates of iron sulfate will result in similar disease suppres - sion observed at higher rates of iron sulfate while lessening the effects of turfgrass thin - Figure 1. (Top) A non-treated plot on an annual bluegrass putting green in Corvallis, Ore. (Bottom) A plot on the same green showing the effects of treatment with 8.5 fluid ounces Civitas Turf Defense/1,000 square feet (27 liters/hectare) + 3.2 fluid ounces DuraPhite 12/1,000 square feet every two weeks in October and November 2017 and April 2018 and 0.25 pound sulfur + 3.2 fluid ounces DuraPhite 12/1,000 square feet every two weeks from December 2017 through March 2018. Both photos were taken on Feb. 1, 2018. Photos by Clint Mattox

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