Characterisation of berry shrivel in Vitis vinifera L. Cultivars in the Stellenbosch wine region

Abstract

Context and purpose of the study – Late season dehydration, bunch stem necrosis, sugar accumulation disorder and sunburn are various types of berry shrivel occurring in vineyards. The incidence of these types of shrivel, and the degree to which it occur are influenced by various factors in the vineyard. These factors include the presence of pests and diseases in the vineyard, genetic traits expressed in certain cultivars, as well as climatic and environmental factors. The occurrence of berry shrivel in the vineyard could negatively impact the quality and quantity of the fruit produced. The aim of this study was to visually characterise the different types of berry shrivel occurring and the corresponding in two cultivars Vitis vinifera L. Chenin blanc and Shiraz in the Stellenbosch Wine region.

Material and methods – In this study the occurrence of berry shrivel in Chenin blanc and Shiraz grapes were studied in two vineyards in the Stellenbosch Wine of Origin district during the 2017/2018 ripening season. Two distinct microclimates were established by implementing a leaf removal treatment in the bunch zone of the canopies on the morning side of some of the experimental panels around véraison, leading to a more exposed microclimate (leaf removal treatment) versus untreated control panels. To confirm microclimatic impacts, loggers were placed in the vineyards to measure the temperatures in the bunch zone of the control and treatment panels. Additionally, grape composition (berry fresh weight, berry volume, total soluble solids, pH and TA was monitored during the growing season for each of the grape cultivars.

Results – Bunches on vines where leaves were removed were exposed to more direct sunlight and temperature extremes, hence sunburn‐related berry shrivel was induced in these vines, especially in the Chenin blanc cultivar. Other types of berry shrivel were however also identified in both cultivars to various degrees during the ripening season, but late stage dehydration also occurred in both cultivars at the overripe stage. It was possible to visually follow the progress of shrivelling throughout the season and a grading scale was implemented to calculate the affected bunch areas. Slight differences were observed in the grape composition of the control (shaded) and exposed (treatment).