Creeping Bentgrass Ultra-sensitive to Atrazine

In one of the few studies of its kind, Cornell researchers Eric Nelson and Cheryl Craft (Dept. Plant Pathology, College of Agriculture and Life Sciences) report the successful suppression of dollar spot in both preventative and curative applications by a biological control agent, the bacteria Enterobacter cloacae, in field experiments on putting greens in New York. While laboratory and greenhouse studies of similar biocontrol agents are not uncommon, investigations under actual field conditions are rare. The two-year study was conducted on 60 year-old native soil putting greens (alkaline clayloam, pH 7.2) at the Country Club of Rochester. Greens turf consisted of a mixture of creeping bentgrass and annual bluegrass, with a natural infestation of dollar spot. In 1988, a one-time-only topdressing with the bacterial agent was applied as a preventive measure, and in a separate experiment a curative application was compared to the fungicide iprodione on highly diseased turf. The preventive application significantly reduced dollar spot as compared to control, and the curative application was as effective as the fungicide. In 1989 monthly preventive treatments of the bacteria were applied, paired with parallel applications of the fungicide propiconazole. The bacterial agent was as effective as the fungicide, both achieving significant suppression of dollar spot as compared to controls. For some strains of bacteria, significant suppression of disease was observed for up to 2 months after application in both the preventive and curative studies. The bacterial agent was considered more effective as a preventive than a curative. The mechanism by which E. cloacae inhibits the fungal pathogen is unknown, but the authors suggest that both an enhanced nitrogen uptake by the plant as well as direct interference with fungal adherence to the host may be responsible. The authors further note that application of suitable bacterial strains could be made during routine topdressing of greens and tees, hence requiring no additional scheduling to achieve the preventive benefit. (From: E.B. Nelson and C.M. Craft. 199