Environmental and Hormonal Effects on Development of Early Bunch Stem Necrosis

Abstract

Factors influencing the development of early bunch stem necrosis (EBSN) were studied using fruiting cuttings of Riesling and Cabernet Sauvignon grapes. Riesling shaded to 10%. 20%, 50%, and 100% full greenhouse light developed more EBSN than unshaded control, and reducing leaf area of Cabernet Sauvignon held at 50% full greenhouse light further enhanced EBSN development. Reducing irrigation frequency without inducing wilt or leaf fall also increased the disorder in Cabernet Sauvignon. Similarly, reducing nutrient levels to 20% of control promoted EBSN in the same cultivar, and, in a parallel experiment, sprays of foliar nutrients pre-bloom reduced the disorder. Field experiments with Gewürztraminer showed that ethephon and chlormequat applied pre-bloom increased berry set. Only the ethephon treatment increased EBSN. Neither influenced final yield. The level of ethephon-induced EBSN was reduced if bunches were avoided during spraying. These results suggest the disorder is exacerbated by conditions inducing stress and may be mediated by endogenous or exogenous ethylene. They also indicate practical ways to reduce EBSN