Disease Progress, Yield Loss, and Control of Xanthomonas fragariae on Strawberry Plants

The progress of angular leaf spot, caused by the bacterium Xanthomonas fragariae, was examined in field plots of strawberry in the 1994 and 1995 seasons. Disease severity increased intermittently to maxima of circa 25% in 1994 and 15% in 1995. Angular leaf spot reduced marketable yield 8.6% in 1994 and 7.7% in 1995, despite differences in disease severity and base marketable yields for the two seasons. Minimal spread of the pathogen occurred from field plots with inoculated plants to plots with non-inoculated plants. A mixture of cupric hydroxide plus mancozeb was applied at the label rate (1×) at 7- to 14-day intervals and at a reduced rate (0.1×) at 2- to 4-day intervals. The bactericidal mixture at the 1× rate significantly decreased disease, but this mixture was phytotoxic; both plant size and yield were reduced. The 0.1× rate was nonphytotoxic and it reduced disease severity in both years and increased yield in 1994. Lesions of angular leaf spot were detected on strawberry transplants imported from nurseries in Canada and northern United States in both 1993 and 1994. X. fragariae was isolated from those lesions.