Reducing Chlorothalonil Fungicide Inputs with Alternative Products to Suppress Dollar Spot.

Four alternative treatments to control dollar spot (Sclerotinia homoeocarpa) were evaluated in 2009 from May 19 through October 13.  Two biological products (Rhapsody, Bacillus subtilis QST 713, and EcoGuard, Bacillus licheniformis SB3086 plus indole-3-butyric acid), a moisture control product (DewCure, oxinane-methyloxirane), and a fertilizer (Urea, 46-0-0) were tested for their ability to reduce curative fungicide (Daconil Ultrex, chlorothalonil) applications.  An untreated control, Daconil Ultrex every 14 days, and curative Daconil Ultrex applications served as comparisons.  Curative applications for dollar spot were implemented using a 5% damage threshold value.  The study was replicated at two Chicago suburb golf course fairways in play.  Individual plots were 4 ft by 6 ft in size and arranged in a randomized complete block design with four replications.  Treatments were applied every 14 days or as needed with a CO₂ backpack sprayer and 8004 nozzles at 40 psi in water equivalent to 2 gal/1000 ft².  Percent plot damage and visual quality (0-9 scale; with 6 = acceptable, and 9 = best) were estimated weekly.  Area under the curve summarized the entire season by analysis of variance using Fisher’s Protected LSD.  Dollar spot levels remained low through July due to cool weather.  Peak development occurred in October with 60% damage in untreated plots.  The number of curative fungicide applications ranged from 4 to 6 in all treatments except DewCure which reduced chorothalonil use and required 2 applications (Glenview, IL – north suburb) or 1 application (Flossmoor, IL – south suburb).  On certain dates, phytotoxicity in DewCure plots did result in unacceptable visual quality.