The biology of the grape bud miteEriophyes vitis(PGST.)

Abstract

THE SEASONAL ACTIVITY of the recently discovered bud-mite strain of the grape erineum mite, Eriophyes vitis (Pgst.), is described in this study, undertaken to provide a basis for developing control measures. Field observation and laboratory studies, conducted on Carignane grape buds at Davis, have shown the grape bud mite to be capable of inflicting severe injury that may result in loss of crop and death of the infested vines. Typical symptoms of bud-mite injury are: deformation of the primordial clusters, distortion of the basal leaves, stunting of the main growing point of the buds, and death of the overwintered buds. Evaluation of mite damage in the field is often complicated by abnormal growth caused by diseases and other grape pests. Morphologically identical with the erineum form, the bud-mite strain of Eriophyes vitis (Pgst.) is distinguishable by the damage it causes and by its habitat on the vine. Infestation was heaviest in the first ten basal buds, the seventh containing the largest number of mites and eggs throughout the season. In the spring, overwintering mites are carried up with the elongating shoots to newly formed buds; they may also crawl up the canes. Progressive penetration of the buds occurs from May to December, infestation of the primordial clusters occurring as early as July and increasing until December. The mortality rate of the overwintering mites, primarily adult females, is usually high. A field experiment with White Malaga grapes showed no relation between estimated degree of bud-mite infestation and growth symptoms or yield.