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

Shiraz decline.

PHOTO 247. Typical of Shiraz decline is the occurrence of characteristic leaf discolouration (as in Photo 246) in conjunction with visually noticeable cracks on the thickened/swollen trunk (at the top of the drip line).

PHOTO 248. An anatomical representation of gradual and increasing necrosis of cells (individual or in adjacent groups) in the cambial zone, which will gradually give rise to an intermittent cambium ring/ girdle. On an annual basis, a serious decrease is eventually induced with regard to the differentiation of sufficient, normally functioning vascular tissue (secondary xylem and phloem) in the vicinity of the affected areas. Not to be confused with the rugose wood c omplex.

160 • A Guide to Grapevine Abnormalities in South Africa