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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96 GOLF COURSE MANAGEMENT 08.14 (Trifolium repens), mouse-ear chickweed (Ce- rastium vulgatum), dandelion (Taraxacum offcinale), cudweed (Gnap alium or Gamo - aeta species) and prostrate spurge (Eup or- bi umistrata) can persist even with the use of sound management practices. Broadleaf herbicides like 2,4-D have been used on put - ting greens since the 1940s for weed control (1,2), but many superintendents today are hes - itant to use broadleaf herbicides on their put- ting greens for fear that turfgrass injury might occur — especially from 2,4-D applications in summer. Labels for many of the herbicides listed in Table 2 neither allow nor restrict ap - plications to creeping bentgrass or hybrid ber- mudagrass greens, leaving liability on the end user in the event undesirable turfgrass injury occurs after application. Mixtures of synthetic auxin herbicides can be used at reduced rates to control broadleaf weeds on putting greens. For example, 2,4-D + MCPP + dicamba (for example, Trimec Classic, PBI/Gordon) can be applied to creep - ing bentgrass putting greens at 1 fluid ounce of formulated product per 1,500 square feet. The label does caution against applications when creeping bentgrass putting green turf is under heat or drought stress and highlights that injury after application will be short- lived. A different formulation (for example, Trimec Bentgrass Formula, PBI/Gordon) is labeled for use on creeping bentgrass greens at rates less than or equal to 1 fluid ounce of for - mulated product per 1,000 square feet (3.18 milliliters/hectare). Trimec Bentgrass For - mula applies less 2,4-D (0.15 pound ae/acre vs. 0.45 pound ae/acre (168 grams ae/hectare vs. 504 grams ae/hectare) than Trimec Classic when applied per label directions. Carfentrazone (for example, QuickSil - ver T&O, FMC Corp.) is a post-emergence broadleaf weed control herbicide labeled for use on creeping bentgrass and hybrid bermu - dagrass putting greens. Rates range from 1.0 to 2.0 fluid ounces/acre (73 to 146 milliliters/ hectare); however, the product can be used at 6.7 fluid ounces/acre (490 milliliters/hectare) for managing silvery thread moss (Bryum ar - genteum). Research in Tennessee indicates Quicksilver applications combined with ap - propriate cultural practices (for example, in- creased nitrogen fertility and sand topdress- ing) control silvery thread moss better than simply spraying the herbicide alone (3). Recent broadleaf research There is very little data on the safety of broadleaf herbicides on putting greens despite pesticide labels that suggest that they can be used without injuring turf. Research was con - ducted at Purdue University and the Univer- sity of Tennessee during 2011-2012 to deter- mine the safety of post-emergence broadleaf herbicides on putting green-height creeping bentgrass turf. An experiment was conducted twice at the W.H. Daniel Turfgrass Research and Diag - nostic Center at Purdue University in West Lafayette, Ind., and the East Tennessee Re - search and Education Center in Knoxville, Tenn., at the University of Tennessee. The Indiana location was Pennlinks creeping Herbicide Rate (fluid ounces/acre) Herbicide injury Indiana (1-9) † Tennessee (0%-100%) ‡ Fall Spring Fall Spring 5 WAA § 2 WAA 6 WAA 2 WAA Applied at the label rate for putting greens 4-Speed 28.8 // 9.0 a // 7.3 bcd 3.3 6.7 abc 4-Speed XT 28.8 8.7 ab 8.0 abc 1.7 6.0 bcd Banvel 16.0 8.3 bc 8.3 ab 0.0 10.0 abc Mecomec 2.5 64.0 8.7 ab 9.0 a 0.0 0.0 d Quicksilver T&O 6.7 # 9.0 a 9.0 a 0.0 0.0 d Trimec Bentgrass 43.2 8.7 ab 9.0 a 0.0 0.0 d Trimec Classic 28.8 9.0 a 8.7 a 3.3 1.7 cd Trimec Encore 28.8 9.0 a 8.3 ab 0.0 1.7 cd Trimec Southern 32.0 9.0 a 8.3 ab 1.7 6.7 abc Applied at twice (2×) the maximum label rate for putting greens 4-Speed 57.6 8.3 bc 7.0 cde — 6.7 abc 4-Speed XT 57.6 8.3 bc 6.7 def — 11.7 ab Banvel 32.0 7.3 d 6.0 ef — 18.3 a Mecomec 2.5 128.0 9.0 a 8.0 abc — 6.7 abc Quicksilver T&O 13.4 # 9.0 a 9.0 a — 0.0 d Trimec Bentgrass 86.4 8.3 bc 8.7 a — 6.7 abc Trimec Classic 57.6 8.3 bc 8.0 abc — 8.3 bcd Trimec Encore 57.6 8.0 c 7.3 bcd — 5.0 bcd Trimec Southern 64.0 8.0 c 5.6 c — 13.3 ab Untreated 9.0 a 9.0 a — 0.0 d P-value 0.0001 <0.0001 NS 0.0041 Note. Product manufacturers are listed in Table 2. † Turf injury in Indiana was rated on a 1-9 scale, where 1 = complete kill, 9 = no injury, and ≥7 = acceptable injury. ‡ Turf injury in Tennessee was rated on a scale of 0-100%, where 0% = no injury, 100% = complete kill, and ≤10% = acceptable injury. § WAA, weeks after application. // Means followed by the same letter within each column are not significantly different. # Application included a nonionic surfactant (NIS) at 0.25% (v/v). Table 3. Injury ratings following applications of broadleaf herbicides to creeping bentgrass putting greens in the fall or the spring in Indiana and Tennessee at label rates and twice (2×) the label application rates. Injury ratings after herbicide applications to creeping bentgrass greens

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