CONTROL OF BOTRYTIS BUNCH ROT OF GRAPE WITH CANOPY MANAGEMENT

Abstract

B. cinerea bunch rot of Chenin blanc grapes was significantly reduced in canopy management field trials established in 1984 and 1985 in Monterey County, California. Treatments consisted of hedging, shoot removal, leaf removal, a movable wire system and a nonmanaged control. Treatments in 1985 were similar, but the movable wire system was omitted. An additional trial in 1985 in Napa County, California, compared the leaf removal treatment with the nonmanaged control. All plots were established in a split-plot design with or without fungicides. Bunch rot control was greatest in the leaf removal treatments. In Monterey, the leaf removal treatments in 1984 and 1985 reduced disease incidence from 11.9 to 1.8 and from 55.0 to 23.9, respectively. Leaf removal also reduced disease severity in the Monterey trials. Percentage rot by wt was reduced from 1.78% in the nonmanaged, nonsprayed control to 0.30% in the vines manipulated by leaf removal in 1984. In 1985, severity was reduced from 15.3% rot/cluster to 2.85% in the leaf removal treatment. Application of fungicide in 1984 significantly reduced disease in all treatments except leaf removal, whereas the reduction in incidence attributable to fungicide was not significant in 1985. In the Napa trial in 1985, leaf removal also reduced disease incidence from 30.52 to 6.17% in the nonsprayed controls. Disease severity was reduced from 3.36% rot/cluster in the intact, nonsprayed control to 0.30% in the nonsprayed leaf removal treatment. Fungicides did not significantly reduce incidence or severity.