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

Hail In general hail induced damage – as associated with the potential and sporadic occurrence of hail in all South African winegrowing areas – is easily identifiable. Although grapevines are especially vulnerable to hail damage early in the growing season, serious damage may be wrought throughout the entire spectrum of phenological stages – in which case the economic impact will obviously be determined by the intensity of the storms and the size of the hailstones (Photos 429 - 433). Lightning Although damage due to lightning is not a common occurrence in vineyards, considerable damage may be inflicted on grapevines, especially in instances where trellis wires are directly hit. In affected grapevines, browning and drying out of leaves and shoots will take place from the tips, while bunches are obviously affected too – a situation which can often be seen in totality across individual rows (Photo 434). In instances where young, soft shoots touch wires directly early in the growing season, shoots will snap and dry out, including flower clusters in adjacent positions – this is very characteristic of the radiation effect that may be caused by lightning (Photo 435). On the other hand thickening may occur in positions where older, partially lignified shoots come into direct contact with the wire. This phenomenon is associated with the healing/filling of cracks by means of callus formation (Photo 436). In addition the drying out of pith sections in such shoots – thereby creating the impression that the inside is hollow – is considered very characteristic of lightning damage (Photo 437). Sulphur burn Young leaves and bunches display a particular sensitivity to sulphur burn in high temperature situations shortly after dusting, and extreme care should be taken when dusting sulphur is used to combat applicable diseases/pests. Young leaves burn from the edges mostly and a typical reddish-brown discolouration takes place, whereafter the leaves curl up and damaged parts harden and dry out (Photo 438). In the case of older leaves burn damage can also occur on sections between the main veins, in addition to the edges – in which case leaves appear normal except for dry, reddish-brown spots between the veins. In berries, sulphur burn is associated with the development of smooth, dark brown to black discolourations (within which cracks occur) – in which case the texture of burnt areas looks hard and may result in asymmetrical berry development (Photos 439 - 441). ABIOTIC ABNORMALITIES Hail, lightning, sulphur burn, bunch stem necrosis and growth arrestment 6.3

272 • A Guide to Grapevine Abnormalities in South Africa