Golf Course Management

NOV 2018

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

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11.18 GOLF COURSE MANAGEMENT 79 CUTTING EDGE Teresa Carson Effects of potassium on a bentgrass green e average putting green receives nearly 4 pounds of K 2 O/1,000 square feet each year. e conventional wisdom is that high levels of potassium confer tolerance to stress caused by disease, drought, cold and traffic, although re - search has not been conclusive in many cases. e objective of this research was to investi - gate the impact of different levels of potassium fertilization on a bentgrass putting green. e six-year study began in 2011 on a USGA put - ting green with Penn A-4 creeping bentgrass (Agrostis stolonifera L.) that was treated with four levels of liquid potassium sulfate, rang - ing from 0 to 6 pounds K 2 O/1,000 square feet/year. ere were no significant differ - ences in chlorophyll index, visual turfgrass quality or clipping yield as a result of treat - ment over the six years. However, tissue po- tassium, Mehlich-3 soil potassium, and mi- chrodochium patch infection all increased as potassium rate increased. Interestingly, potassium removed in clippings was much greater th an the potassium extracted by both Mehlich-3 and a much stronger extractant (1 M HNO 3 ). is suggests that plant potassium was taken up from a non-exchangeable pool. Hence, traditional soil-testing methods may be inadequate for estimating available potas - sium in sand-based root zones. e total soil potassium in the zero-potassium treatment in - creased as a result of topdressing with a sand th at contained 0.7% total soil potassium and was composed of 78% quartz, 17% potassium feldspar minerals, and 5% hornblende. With topdressing sand being the only significant potassium input, the increase in potassium was a result of the potassium minerals in the sand being added faster than the plant could take them up. e potassium derived from the sand was sufficient to produce a stand similar to (and often better than) the treatments fer - tilized with potassium. — P.V. Bier (Peter.Bier@ usma.edu), United States Military Academy, West Point, N.Y.; and D. Soldat, Ph.D.; P. Koch, Ph.D.; and M. Persche, University of Wisconsin-Madison Reducing Poa annua in zoysia fairways Fraze mowing removes aboveground bio- mass to a depth of 2 inches (5 cm) while al- lowing turfgrass to re-establish via below- ground rhizomes. Because >80% of viable annual bluegrass (Poa annua) seed is in the top 0.4 inch (1 cm) of soil, we hypothesized that fraze mowing might provide effective non-chemical P. annua control, particularly where herbicide resistance has limited chemi - cal control options. Field research was con- ducted from 2015 to 2017 at the University of Tennessee-Knoxville on a zoysiagrass (Zoysia japonica "Meyer") fairway naturally infested with P. annua. Turf was fraze-mowed (1 inch [2.5 cm] depth) in June each year, with debris collected and discarded. Control plots (7.9 × 7.9 feet [2.4 × 2.4 meters]) that were not fraze- mowed were included in each replication for comparison. Each spring, P. annua infesta- tions were quantified via plant counts. Soil cores removed from the center of each plot in spring underwent soil seedbank analysis at Purdue University (West Lafayette, Ind.). Germination assays in this analysis quantified the total number of weed seeds in each core and the species, type and life cycle of weeds present. In field studies, fraze mowing in June significantly reduced P. annua plant counts (26%) the following spring. Our findings sug - gest that summer fraze mowing can reduce P. annua populations in zoysia turf, but this technique may not provide acceptable control when used alone and should be incorporated into a diversified weed management program. — J.T. Brosnan, Ph.D. (jbrosnan@utk.edu), and G.K. Breeden, Ph.D., University of Tennessee-Knox - ville; and A.J. Patton, Ph.D., and Q.D. Law, Purdue University, West Lafayette, Ind. Earlier versions of these summaries were pub- lished in the 2017 ASA-CSSA-SSSA Meeting Abstracts, ASA, CSSA and SSSA, Madison, Wis. Teresa Carson (tcarson@gcsaa.org) is GCM 's science editor. Photo by J.T. Brosnan Photo by Douglas Soldat

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