Clarireedia jacksonii sp. nov. formerly Sclerotinia homoeocarpa F.T. Bennett, one of the causal agents of dollar spot, is the most widespread pathogen in turfgrass systems. Dollar spot (DS) affects both cool- and warm-season grasses, during a wide range of environmental conditions. Field studies were conducted at Clemson University, Clemson, SC, on a creeping bentgrass [Agrostis stolonifera L. var. palustris (Huds) cv. Crenshaw] putting green for 2 consecutive years from August to October in year 1 and July to September in year 2. The objective of the studies was to evaluate biological control agents (BCAs) and synthetic fungicides at reduced rates for their efficacy controlling dollar spot. Four replications of 1.5 × 1.5-m plots were used in the experimental design. Treatments included the following: Bacillus subtilis (BS); plant extract oils (EO) including clove oil + wintergreen oil + thyme oil; extract of Reynoutria sachalinensis (RS); Bacillus licheniformis (BL); chlorothalonil (CL); and azoxystrobin + propiconazole (AzP). Synthetic fungicides were used at reduced rates in combination with biological control agents, to evaluate curative control efficacy of various combinations. All reduced synthetic programs, except CL + EO, provided acceptable disease severity (≤15%) at the end of year 1 and acceptable (≥7) turfgrass visual quality. Azoxystrobin + propiconazole, CL, AzP + BL, AzP + EO, AzP + BS all provided ≤15% disease severity and ≥7 visual turfgrass quality 14 days after the last application in year 2.

Clarireedia jacksonii sp. nov. Formerly Sclerotinia homoeocarpa F.T. Bennett, the causal agent of dollar spot (DS), is the most destructive pathogen in turfgrass. Symptoms appear as circular patches 10-40 mm in diameter with small tan lesions surrounded by a darker band, sometimes presenting an hour glass appearance. A multi-year study was initiated with the objective of determining the effi cacy of biological control agents (BCA) and tank mixes of BCA's and synthetic fungicides on DS control. Nutrient source was also evaluated to determine any interaction with the BCA's and tank mixes. In vitro studies evaluated the effi cacy of synthetic and BCA's for C. jacksonii control. Quarter strength potato dextrose agar was amended with ¼, ½ and full labeled rates of various products. Chlorothalonil at all rates provided greatest (> 90%) control of C. jacksonii for study duration. Biological control agents provided best effi cacy at ¼ and ½ label rates. Streptomyces griseoviridis provided least effi cacy and may have exacerbated formation of C. jacksonii. Preventative fi eld evaluations for synthetic and BCA's provided different results between two study years. In Year 1, all treatments had < 15% disease severity for the duration of the study. In year 2, disease pressure was extremely elevated. Synthetic program 1, centered on azoxystrobin + propiconazole applications and conventional fertility sources, provided best results with < 5% disease severity for the duration of the study. Reduced synthetic program 1, and synthetic program 2 followed closely with < 10% disease severity. Reduced synthetic programs were based on monthly applications of either chlorothalonil or pyraclostrobin every 30 day, alternated with biofungicide applications. Synthetic program 2 utilized rotation applications of pyraclostrobin and chlorothalonil every 14 days. Organic programs, utilizing only biofungicides and organic fertility sources, provided the least amount of control and exceeded the 15% threshold by the second month of the evaluation period. In vitro and preventative fi eld evaluations of potential biological control agents and synthetic fungicides for control of Clarireedia jacksonii sp. nov.