Monday, November 13, 2006 - 10:00 AM
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Dollar Spot Severity as Influenced by Irrigation Practices and Plant Protection Chemicals.

Steven J. McDonald1, Peter Dernoeden1, and Cale Bigelow2. (1) University of Maryland, Dept of Plant Science & LA, College Park, MD 20742, (2) Purdue University, Dept of Agronomy, West Lafayette, IN 47907-4773

Creeping bentgrass (Agrostis stolonifera L. var palustris (Huds.) Farw.) is commonly grown on golf fairways, but it can be chronically affected by dollar spot (Sclerotinia homoeocarpa F. T. Bennett; DS) disease.  This field study assessed the influence of two irrigation regimes (light and frequent versus deep and infrequent) and six chemical treatments including: chlorothalonil (tetrachloroisophthalonitrile); paclobutrazol (4-chlorophenyl) methyl-alpha (1-1 dimethyl)-1h-1, 2,4 triazole-1 ethanol; PB: polymeric polyoxyalkylene 95% oxoalkonyl hydroxyl polyodlalkane diyl 5%; wetting agent WA); chlorothalonil + PB, chlorothalonil + WA and chlorothalonil + PB + WA on dollar spot severity over a three year period.  Turf was ‘Crenshaw’ creeping bentgrass, which was maintained under fairway conditions.  Dollar spot was more severe in late summer in creeping bentgrass that received infrequent irrigation versus frequent irrigation in 2002 and 2004.  Soil moisture levels above 0.25 cm3 cm3 were associated with an improved ability of chlorothalonil, PB, and WA to suppress dollar spot in late summer.  Paclobutrazol (40 to >60%) and WA (30 to 50%) often suppressed dollar spot, and sometimes there was improved dollar spot control when tank-mixing PB, but not WA, with chlorothalonil.