Golf Course Management

MAR 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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03.19 GOLF COURSE MANAGEMENT 85 CUTTING EDGE Teresa Carson This research was funded in part by the United States Golf Association. Long-term dynamics and management requirements of sand-capped fairways As golf course irrigation water quality con- tinues to decline, sand-capping of golf course fairways is increasing. A three-year Texas A&M study evaluated influences of sand- capping depth by subsoil texture on Tifway bermudagrass fairway quality and perfor - mance. Sand-capping depths of 0, 2, 4 and 8 inches were evaluated atop both clay and loam subsoils. rough traditional water-release curve measurements, an "optimal" capping depth of 8 inches had been recommended to achieve a balance of air to water-filled porosity in the root zone. However, at the conclusion of the study, the 8-inch depth was found to result in overly dry surface conditions, periodic de - cline in quality, and hydrophobic conditions in the thatch layer. e "suboptimal" 0-, 2- and 4-inch sand-caps all outperformed the 8-inch cap for all measured parameters. Because of the high levels of sodium (~300 ppm) in the irrigation water used in the study, rapidly in - creasing subsoil SAR was also noted. Based on the findings of the earlier study, the objec - tives of this study are to evaluate longer-term (years 4-6) changes in turf performance, soil physical properties and cultural management requirements of sand-capped fairway plots. We are assessing low- to high-input manage - ment intensities involving various combina- tions of wetting agents and gypsum applica- tion techniques to maintain sand-cap and subsoil physical integrity. Results to date sug - gest that a single high-rate application of gyp- sum early in the year may be more effective at reducing subsoil SAR than monthly low-rate applications throughout the season. Wetting agents are showing the greatest benefit with deeper rather than shallower capping depths. — Will Jackson Bowling; Benjamin Wherley, Ph.D. (b-wherley@tamu.edu); Kevin J. McInnes, Ph.D.; and Tony L. Provin, Ph.D., Texas A&M University, College Station, Texas Resistance to new broad- spectrum fungicides SDHI Dollar spot, which is caused by Sclerotinia homoeocarpa (now Clarireedia species), is one of the most persistent and resilient diseases on amenity turfgrasses. Repeated applica - tions of fungicides have led to resistance to the benzimidazole, dicarboximide, and ste - rol demethylation inhibitor classes, which has already been reported in dollar spot field populations across North America. Recent re - ports of field resistance to the next-generation succinate dehydrogenase inhibitor (SDHI) has been alarming to golf course superinten - dents who depend heavily on SDHIs for dol- lar spot control. Genetic mechanisms of the SDHI resistance are complex. Research with dollar spot isolates collected from golf courses and research plots experiencing field failure in the U.S. and Japan has revealed that mul - tiple different mutations allow for differential sensitivities to the five SDHI active ingredi - ents labeled for dollar spot control (boscalid, fluopyram, fluxapyroxad, isofetamid and pen - thiopyrad). Some of the mutations are highly resistant to all SDHIs, while others are resis - tant only to some. One type of mutation ac- tually becomes more susceptible to fluopyram. erefore, where there is suspicion of reduced efficacy of SDHIs, it is important for super - intendents to have information on the type of mutations existing on their site before ap - plying SDHIs. Recommended management strategies include tank-mixing or alternating with partner fungicides with low-risk resis - tance and limiting the number of applica- tions per season. However, future research should focus on developing an integrated pest management approach for dollar spot man - agement by implementing effective cultural practices, weather-based disease forecasting and using molecular diagnostic tools to initi - ate long-term monitoring of resistant popula- tions. — Geunhwa Jung, Ph.D. (geunhwaj@gmail. com), University of Massachuetts, Amherst Teresa Carson (tcarson@gcsaa.org) is GCM 's science editor. Photo by Will Jackson Bowling Photo by Geunhwa Jung

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