Residual efficacy ofTyphula phacorrhizaas a biocontrol agent of grey snow mold on creeping bentgrass

Isolates of the biocontrol fungus Typhula phacorrhiza were evaluated in field tests over a 5-year period for suppression of grey snow mold caused by Typhula incarnata and Typhula ishikariensis. Of the hundreds of T. phacorrhiza isolates collected from across southern Ontario in the spring of 1994, 42 were cultured on mixed grains and applied in the late fall to creeping bentgrass (Agrostis palustris) at a rate of 200 g/m2 (4 x 105 cfu/m2) along with inocula of T. incarnata or T. ishikariensis at 10 g/m2 (2 x 104 cfu/m2). In late fall of each year from 1995 to 1998, T. incarnata and T. ishikariensis were reapplied to the same plots, but not T. phacorrhiza. Plots were rated for disease after snowmelt in each year from 1995 to 1999. During the first three years, high positive correlations of winter injury were found between the suppression trials, with several isolates showing significant control of grey snow mold. By the fourth year after inoculation, suppression of snow mold in plots treated with the most efficacious T. phacorrhiza isolates had severely declined and there were no significant differences in winter injury between plots treated with T. phacorrhiza isolates in the fourth and fifth years.