A pruning technique for saving vineyards severely infested by the grape vine bud mite Colomerus vitis (Pagenstecher) (Eriophyidae)

Abstract

The highest proportions of large populations of the grape vine bud mite Colomerus vitis (Pagenstecher) were found in the basal ten buds on canes of Chenin Blanc throughout a year of study. The distribution of mites along the canes is explained in terms of their distribution within the mature overwintering buds in which the basal 7–10 nodes are already present and infested by C. vitis. Although the basal ten buds all maintained high bud-mite populations, the damage inflicted to the buds was greatest in buds at the basal two nodes, and declined significantly in buds located at nodes 4 and 6, and 8 and 10, on mature overwintering canes, respectively. A comparison of various pruning techniques shows that vines severely infested and damaged by C. vitis should be pruned back to six buds for one season. This uses the healthier buds at nodes 5 and 6 to produce the next season's growth, while reducing yield lost to C. vitis from 56% to 35%. It is recommended during the subsequent year (a) that the basal four canes be removed to reduce bud-mite populations in the vineyard; (b) that the usual pruning technique of leaving only two buds per bearer be reverted to, and (c) that the effective chemical control programme against C. vitis be regularly applied during spring. In this way vineyards that are severely damaged by C. vitis can be saved while yield can be increased during the year that corrective measures are applied.