Department of Plant Pathology

Phomopsis cane and leaf spot is a disease that can be economically important in California during wet years along the northern coast and in the northern San Joaquin Valley. A field trial was conducted in Solano County, CA to evaluate the efficacy of several registered and experimental fungicides on control of Phomopsis cane and leaf spot on Thompson seedless grapes. Fungicide treatment significantly affected leaf severity. Kresoxim methyl (at 6.4 oz/acre) and pyraclostrobin + boscalid provided the best protection; kresoxim methyl (at 4.0 oz/acre) and Streptomyces lydicus WYEC108 (12 oz/acre) also reduced leaf severity. Shoot disease severity also differed significantly among treatments; data suggested that the best disease control was achieved by treatment with pyraclostrobin + boscalid or kresoxim methyl (both application rates).