Golf Course Management

OCT 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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10.18 GOLF COURSE MANAGEMENT 75 CUTTING EDGE Teresa Carson Managing mini-ring in ultradwarf bermudagrass e turf disease rhizoctonia leaf and sheath spot (RLSS), commonly referred to as "mini- ring," has been problematic in ultradwarf ber - mudagrass (UDBG) putting greens since the late-1990s. In the transition zone, symptoms appear in late summer as frog-eye patches 4 to 18 inches (10-46 cm) in diameter and be- come more distinct in the late fall as UDBG growth slows. Symptoms are often most severe in UDBG that is managed with low nitrogen fertility. e purported causal agent, Rhizocto - nia zeae, is frequently isolated from symptom- atic turf, but disease epidemiology has not been extensively researched. Seasonal activity of R. zeae was studied by performing isolations from a UDBG putting green with RLSS symptoms from June through October in 2016 and 2017. Rhizoctonia zeae was isolated from UDBG leaf tissue in the months of June, July, August and September, yet isolation frequency was greatest in the latter two months. To investi - gate the impact of nitrogen on RLSS develop- ment, in 2016 and 2017, nitrogen, in the form of ammonium sulfate or urea, was applied to a MiniVerde and a TifEagle putting green at rates of 0.10, 0.20 and 0.30 pounds (45.3, 90.7 and 136.0 grams) nitrogen per growing week. RLSS severity increased in both cultivars as the rate of ammonium sulfate increased. In contrast, RLSS severity decreased as the rate of urea increased. It appears that RLSS is con - sistently associated with R. zeae and that in- fection likely takes place from midsummer to early fall. UDBG fertilized with urea showed less disease severity than turf treated with am - monium sulfate. — Luke Dant (ldant@clemson. edu) and S.B. Martin, Ph.D., Clemson University, Florence, S.C.; L.B. McCarty, Ph.D., Clemson Uni - versity, Clemson, S.C.; and J.P. Kerns, Ph.D., North Carolina State University, Raleigh Kentucky bluegrass for turfgrass water conservation Historically, Kentucky bluegrass has been considered a poor choice for turfgrass areas in arid and semi-arid climate zones as it is considered a high-water-use grass. However, research conducted at New Mexico State University indicates that such a notion may be misleading and does not tell the whole story. ere is no question that warm-season grasses such as bermudagrass and buffalograss have greater drought tolerance and lower ir - rigation requirements than traditional cool- season grasses. However, quality expectations and seasonal usage may force turf managers and superintendents to grow cool-season in - stead of warm-season grasses. Current re- search (e.g., NTEP low-water-use trials) looks at either turfgrass performance under perma - nently reduced irrigation (chronic drought stress) or the length of time grasses main - tain quality and green color after irrigation is withheld. However, natural or artificially (e.g., temporary watering restrictions) im - posed periods of droughts will eventually end, and when they do, knowledge about which grasses recover more quickly after drought is needed. Ongoing trials at New Mexico State University (arid, USDA plant hardiness zone 8) aim at investigating irrigation requirements and drought recovery of different cool-season turfgrasses. First results indicate that if perfor - mance during drought and speed of recovery after drought stress are factored into a deci - sion, several Kentucky bluegrass varieties per- form better than perennial ryegrass and equal to or better than tall fescue varieties. e trials will be conducted over several years to find out if these results also hold true in the long term. — Bernd Leinauer, Ph.D., and Matteo Serena, Ph.D., New Mexico State University, Las Cruces Teresa Carson (tcarson@gcsaa.org) is GCM 's science editor. Photo by Matteo Serena Photo by Luke Dant

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