Bunch rot of Rhine Riesling grapes in the lower south-west of Western Australia

Abstract

A bunch rot disorder of Rhine Riesling grapes was investigated during the 1976-77 and 1977-78 seasons in south-west of Western Australia. Fungi isolated from immature berries at or just after flowering were not identical to those isolated from rotting berries at harvest. A wide range of fungi, including Aureobasidium pullulans (de Bary) Arnaud, Botrytis cinerea Pers. ex Fr., Rhizopus, Aspergillus, Penicillium and Alternaria spp., was isolated from rotted berries at harvest. More than 98% of rotting berries showed berry splitting or cracking, or both, at the pedicel end of the grape. Berry thinning of bunches by hand resulted in the almost complete elimination of berry splitting and cracking and a corresponding decline in bunch rot levels. The yield of unrotted bunches from the thinned vines was more than twice that for the unthinned ones; however, thinning reduced overall total vine yields by 63% compared with yields from unthinned vines.