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11.16 GOLF COURSE MANAGEMENT 85 CUTTING EDGE Teresa Carson Does irrigating dormant bermudagrass pay off? Despite the inactivity and lack of transpi- ration of warm-season grasses during winter dormancy, the general recommendation is to keep the crown of the plant moist and ac - tive to avoid winter injury. A study was con- ducted at New Mexico State University to test the usefulness of this practice by inves - tigating the effects of four irrigation regimes on spring green-up of Princess-77 bermuda - grass (Cynodon dactylon L.). The irrigation consisted of 0.12 inch (3 mm) applied ei - ther once per week, once every two weeks, or once monthly. The control treatment re - ceived no irrigation. Each treatment was rep- licated three times. Percentage of green cover was determined every two weeks starting on March 13 and continued until 100% cover had been reached. On March 30, daily irri - gation was resumed based on reference ET for short grass to allow bermudagrass to fully recover. Statistical analyses indicate signifi - cant differences among treatments. Plots that were irrigated weekly reached 50% coverage 15, 19 and 24 days faster than plots irrigated biweekly, monthly or not at all, respectively. However, 95% coverage was reached equally fast for weekly and biweekly irrigated plots compared with monthly irrigated plots and control plots. Our results indicate that small irrigation amounts applied either weekly or every other week during winter dormancy will result in faster spring green-up. How - ever, more research is necessary to investigate irrigation frequency and exactly how much water is needed for earliest green-up. — Mat- teo Serena and Bernd Leinauer, New Mexico State University, Las Cruces, N.M. Trinexapac-ethyl and auxin affect creeping bentgrass under deficit irrigation Creeping bentgrass quality declines in summer. Trinexapac-ethyl (TE) is a plant growth regulator commonly used to suppress shoot growth, but its impact on root growth and drought tolerance has not been conclu - sively studied. This study was designed to investigate the effects of TE applied at 0.125 ounce a.i./1,000 square feet (4.5 mg a.i./ square meter), alone or in combination with auxin (indole-3-butyric acid, IBA, 2 µM), on root growth and quality of creeping bent - grass under two soil moisture regimes: well- watered and mild drought stress. Treatments (TE, IBA and TE+IBA) were applied to the foliage biweekly. Two weeks after initial treat - ment, the grass was subjected to either well- watered or deficit irrigation (compensating for 70% to 30% loss via evapotranspiration) for 42 days. Under deficit irrigation, the TE, IBA and TE+IBA treatments increased root viability, and TE+IBA also increased root bio - mass relative to the control. TE and TE+IBA improved turf quality, net photosynthetic rate and transpiration rate under deficit irri - gation. TE, IBA and TE+IBA increased leaf indole-3-acetic acid and abscisic acid content under deficit irrigation. TE and TE+IBA also boosted leaf cytokinin isopentenyl adenosine content under deficit irrigation. The results suggest foliar application of TE plus auxin may improve creeping bentgrass quality, root function and physiological fitness under defi - cit irrigation conditions. — Xunzhong Zhang, Ph.D. (firstname.lastname@example.org); Erik H. Ervin, Ph.D.; and Alyssa Hamill, Virginia Tech, Blacksburg, Va. Teresa Carson (email@example.com) is GCM's science editor. Photo by Matteo Serena Photo by Xunzhong Zhang