California and Michigan strains of Xanthomonas campestris pv. poannua were compared as biocontrol agents for the annual and perennial subspecies of annual bluegrass. Additionally, inoculation frequency was evaluated for improved control of the perennial subspecies in New York. The two bacterial strains were similarly virulent to annual bluegrass in both growth chamber and field tests. When inoculated once per week for 4 wk, the annual and perennial subspecies were controlled 92 and 82% in growth chamber tests, but only 11 and 7% in field tests, respectively. Control of established annual bluegrass in the field was improved to a maximum of about 40% by increasing inoculation frequency to three times per wk for 4 wk, but recovery occurred 2 to 5 wk after inoculations were discontinued. Creeping bentgrass was not affected by the bacterium.
