A Guide to Grapevine Abnormalities in South Africa - P.G. GOUSSARD

INTRODUCTION

O ptimal in-vineyard performance of individual vines, associated with the sustainable and profitable cultivation thereof, shows a close kinship with the health of the plant material as well as the continuous and correct application of practices which best meet the cultivation preferences and needs of the relevant cultivars in different regions. The occurrence and further development of any abnormality(ies) – whether associated with either biotic (vineyard diseases and pests) or abiotic (environmental condition) factors, or with injudicious/faulty establishment, vine development and continuous cultivation practices – will with hardly any exception contribute to a negative influence on the productive life expectancy of vines over the short or longer term. In this book, vine abnormalities – those based on the occurrence and/or causes thereof in terms of specific problem situations – are divided into the following categories, namely: (i) plant material problems; (ii) fungal diseases; (iii) bacterial diseases; (iv) virus and virus-like diseases; (v) grapevine pests; (vi) abiotic abnormalities; (vii) genetic deviations; (viii) deficiencies and toxicity of nutritional elements; (ix) herbicide phytotoxicity; (x) injudicious/faulty cultivation practices/actions and (xi) varia. With the abovementioned as background, concise descriptions regarding the visual appearance of specific phenomena are based chiefly on related literature with the emphasis on textbooks (Perold, 1927; Du Plessis, 1947; Winkler et al., 1974; Bovey et al., 1980; De Klerk, 1981; Marais, 1981; Saayman, 1981; Smit, 1981; Galet, 1978, 1995; Ferreira & Venter, 1996; Bailey et al., 1998). In addition to this, abnormality interventions are illustrated with photographic material – to provide cryptic but basic captions with individual examples as elucidation. Although the focus is chiefly on the appearance and description of the most typical abnormalities, due to the extensive diversity thereof, a concerted effort was also made to include less known phenomena which occur less commonly, where applicable. As this presentation mainly concentrates on the visual appearance/observations of specific abnormalities, descriptions (except in unusual and applicable cases) of: (i) scientific designations of causal organisms and their life cycles: (ii) specific disease and pest control programmes and (iii) the mechanisms of operation of control, prevention and eradication substances, are not included. In addition it is of cardinal importance that, if there is any doubt about the identification of a problem on the grounds of visual appearance, an expert should be consulted in such cases for confirmation. The overarching objective is based on correct identification of the problem, to allow stakeholders in the industry to act timeously and effectively in terms of control and/or corrective strategies.

A Guide to Grapevine Abnormalities in South Africa • 3