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

Stem grooving.

conjunction with ongoing development/formation of cracks – eventually assuming (especially noticeable in mature trunks) a thickened, coarse and cracked appearance (Photo 221). Leaves on infected grapevines appear pale yellow early in the season, are smaller than normal and curl slightly inwards. In the case of red grape cultivars the leaves turn red very early – including primary and secondary veins – and eventually become dark brown and even purple (Photo 222). Due to the latent incidence of corky bark-associated viruses (many cultivars are bearers without any symptoms) accurate identification is considerably restricted. In such instances hardwood indexing (LN 33 as indicator cultivar) play a valuable role to reveal the true cause – based on the expression of specific and characteristic abnormalities associated with corky bark (Photo 223).

PHOTO 208. An example where delayed bud burst occurs in combination with the dieback of shoot and trunk sections – a situation that goes hand in hand with stem grooving-associated viruses. Note the coarse appearance of bark in the 14:00 position especially where obvious signs of grooving are visually detectable.

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