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

PART 4

irregular ripening. Although these phenomena can be considered to be typical of virus- associated diseases, they are not specific and expert advice should be sought to prevent confusion with other possible causes. In the light of the fact that specific anatomical reactions/changes can by caused in virus-infected vines, a basic knowledge of normal vine anatomy could serve as a useful additional tool regarding problem identification. In general a thorough knowledge of abnormalities linked to virus-associated diseases/ phenomena – especially should they occur in combination within the same vines – should/ could be considered to be a high priority, whether it is linked to phytosanitary selection or even the top-working of existing grapevines to alternative cultivars or not. Should such abnormalities thus be associated with abovementioned phenomena, it is indicative that the phytosanitary status of the plant material is not up to standard – which could seriously limit future performance of vegetative descendants in the vineyard. Overall one must keep in mind that when virus diseases occur to such an extent that the visual appearance thereof is associated with specific abnormalities, a lasting/irreversible problem situation is already in place which cannot be controlled or eradicated with chemicals/integral spraying programmes – which leaves the uprooting and burning of infected vines as virtually the only alternative. Naturally only the economically most important and dangerous diseases are highlighted, while examples which occur locally, but are of lesser economic importance, were not included. The expection is that portrayed examples regarding characteristic, visually observable abnormalities which occur with individual diseases, may offer stakeholders not only the opportunity of correct identification procedures, but may also assist in the management of infected vineyards in such a way that further spread can be curtailed as efficiently as possible.

A Guide to Grapevine Abnormalities in South Africa • 111

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