FERTILISER GUIDELINES FOR THE WINE INDUSTRY

FIGURE 10: Die-back due to soil acidity, Roussillon.

The red leaf phenomenon in Barlinka table grapes in the Hex Valley was initially considered a Cadefciency, due to low Cacontents of affected leaves. It was found however, that it was caused by a plant transferable pathogen, probably similar to the grapevine red blotchassociated virus (GRBaV) which was recent ly identified in the USA and is only observed on red grape cultivars (Fig. 11). Berry stem necrosis is a physiological disorder found in certain cultivars under certain growing conditions (climate, N-nutrition). It is characterised by black, necrotic girdling ring lesions around bunch stems and pedicels from veraison onwards, through which the vascular bundles are abscised, resulting in berries wilting and not ripening (Fig. 12). The necrotic tissue is characterised by low Ca-contents, of which the causes and meganism are not known. Leaf and bunch nutrition with Casprays have proven ineffective, possibly due to the dominant apical movement of Ca in the plant.

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