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

Crown gall.

in respect of the phytosanitary quality of propagation material being implemented at registered nurseries, the incidence of crown gall in one-year-old grafted grapevines may be considered something of the past – while it was common in years gone by, especially in uncertified material. One should always be careful not to ascribe swollen, coarse graft unions to crown gall exclusively, even when typical galls occur on the rootstocks of fully- grown grapevines (Photo 158). In this specific instance the swollen parts on the trunk – which was abnormally thickened and had short internodes and an exceptionally small pith – as well as on the cordon arms evolved further and eventually contributed to early dieback (Photos 159, 160, 161, 162 & 163). A closer analysis of these swellings (encircled by loose, cracked parts of the bark), indicates the prevalence of numerous latent buds (Photo 164). In conclusion it may be pointed out that although crown gall is present in this specific instance, additional aspects/factors contributed to the eventual problem situation. Before speculating about possible growth regulator imbalances, inter alia, it is strongly recommended that thorough laboratory analyses be done.

PHOTO 154. A characteristic of crown gall is the development of typical galls on grapevine trunks near the surface of the soil. In this specific instance the formation of galls resulted from initial wounding.

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