Golf Course Management

AUG 2014

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

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100 GOLF COURSE MANAGEMENT 08.14 Reptiles, spring-break undergraduates and hybrid bermudagrass — they all really like sun - shine. In fact, all three of those groups would likely lie happily prostrate in sun for most of the day, given the chance. Hybrid bermuda- grass, however, keeps getting shoved into shade, because we like trees on our golf course — trees getting in the way of the shot, trees artfully ar - ranged around the green, trees framing the hole in resplendent glory. Damn those trees. Suffce it to say that hybrid bermudagrass and trees don't get along all that well, and thus managing bermudagrass in the shade is a re - search topic of interest. The top research scien- tists that study bermudagrass and shade are in Dr. Bert McCarty's research group at Clemson University. In 2005 they examined the com - bined effects of mowing height, growth pro- moters and various hours of sunlight on TifEa- gle bermudagrass. From June to August of two years, shade cloth was placed over the putting green to pro - duce 12, eight or four hours of sunlight. These plots of sunlight levels were split into smaller plots to which growth promoters were ap - plied: (1) trinexapac-ethyl applied every three weeks (0.035 pound ai/acre [0.039 kilogram ai/hectare]); (2) gibberellic acid applied every two weeks (0.055 pound/acre [0.062 kilo - gram/hectare]); (3) additional nitrogen applied every two weeks (22 pounds nitrogen/acre; ½ pound/1,000 square feet [24.5 kilograms/hect - are]) using an 18-4-15 N-P-K fertilizer; and (4) the control. The split plots were split again in mowing height ( 1 ⁄8 or 3 ⁄16 inch daily [3.2 or 4.7 millimeters]). All the plots received 22 pounds nitrogen/acre biweekly. Highest turfgrass quality was found in plots that received 12 hours of sun and added nitrogen, regardless of mowing height. As the amount of sunlight was reduced, turf quality decreased, although bermudagrass grown in eight hours of sun still had acceptable quality. If only four hours of sunlight was provided, turf quality was unacceptable, except when trinexapac-ethyl was applied and the turf was mowed at the higher height of 3 ⁄16 inch. In that case, the quality was equal to that found in some of the other treatments that received more sun. Applying the additional ½ pound of ni - trogen/1,000 square feet every two weeks also helped lateral regrowth of the bermudagrass, but only when the grass received 12 or eight hours of sunlight. Adding trinexapac-ethyl and mowing low produced the slowest lateral regrowth and, regardless of treatment, lateral growth was always poorest in the most shaded plots. The combination of only four hours of sun and extra nitrogen decreased total non - structural carbohydrates, and the addition of trinexapac-ethyl or gibberellic acid did not im - prove total nonstructural carbohydrates. Basically, differences in TifEagle bermu - dagrass quality, lateral growth, chlorophyll content and total nonstructural carbohydrates were fewer when sun was supplied at 12 or eight hours a day. So, a little bit of shade did not horribly affect the bermudagrass. Things got ugly and turf quality declined substantially when sunlight was reduced to only four hours a day. At that level of sunlight, applications of trinexapac-ethyl and a higher height of cut ( 3 ⁄16 inch) were needed to maintain any acceptable level of turf quality. It's important to remember that this study ran for only three months in each summer, and then the shade covers were removed. Thus, the results may not fully refect what can happen to a putting green that is shaded for most of a growing season, nor would they account for ad - ditional stresses such as tree root competition. Regardless, this research was an excellent start - ing point to clearly show that extra nitrogen and/or trinexapac-ethyl, and increased mow - ing heights, can go a long way in helping ber- mudagrass handle shade. Source: Bunnell, B.T., L.B. McCarty and W.C. Bridges Jr. 2005. 'TifEagle' bermudagrass response to growth factors and mowing height when grown at various hours of sunlight. Crop Science 45:575-581. Beth Guertal, Ph.D., is a professor in the department of agronomy and soils at Auburn University in Auburn, Ala., and the incoming editor-in-chief for the Agronomy Society of America. She is a 17-year member of GCSAA. Beth Guertal, Ph.D. guerta@auburn.edu twitter: @AUTurfFert Here comes the sun (verdure) Soil Physical and Chemical Properties: The Analogy Beth Guertal, Ph.D., will present a GCSAA webinar on soil chemical and physical properties, using food to illustrate important concepts like cation exchange capacity, bulk density and infltration. The 90-minute event will take place Sept. 25, 2014, at noon CDT. Read more and enroll online at www.gcsaa.org/Education/ Webcasts/Upcoming-Live/Sept-25-Soil- Physical-and-Chemical-Properties-The- Analogy-Webinar or call GCSAA Professional Development at 800-472-7878.

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