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

are eaten from the edges in a linear pattern until practically the petioles only remain and (ii) the occurrence of characteristic, ball-shaped excretions in individual cases. Spring beetles Spring beetles are approximately 2 to 3 cm in length, brightly coloured and make a loud buzzing noise when they fly. Although various kinds of fruit are affected by the feeding activities of adults, they are not considered a matter of concern in grapes. In recent times, spring beetles have nevertheless developed into an important grapevine pest in the Orange River irrigation area, whereafter establishment as a recognised phenomenon has spread to practically all the winemaking regions. The beetles occur in large numbers in summer, when leaves may be eaten to the extent that practically only the principal veins remain intact. Although they are associated with characteristic feeding patterns (Photos 367 & 368), it is possible to confuse the damage with other causes – in which case it is strongly recommended that expert advice be obtained. Wilting beetles Although the sporadic incidence of wilting beetles is well known in the South African grapevine industry, large-scale damage associated with feeding activities is not deemed exceptionally important. However, should environmental conditions become conducive to epidemic pest numbers, serious damage may be inflicted on active shoot growth early in the growing season – especially in young grapevines, as well as in instances where homogeneous shoot lengths in trellised grapevines enjoy a high priority. Feeding actions are associated with the insertion of a stylet – with which cell sap is extracted from the vascular tissue – just below the curve in an actively growing shoot tip (Photo 369), thus creating the impression that the latter is sucked out to the extent that it is subject to wilting and subsequent desiccation (Photo 370). According to available literature, however, such situations are mostly associated with the harmful secretion of saliva during feeding. Thrips Ever since the incidence of and damage, as caused by the feeding activities of thrips on grapevine leaves and grape berries in particular, were first detected in the Porterville area, this pest phenomenon has systematically spread to practically all local winegrowing regions. Thrips have biting-sucking mouth parts, used to grate or penetrate plant tissue surfaces, whereafter they suck up cell sap that have thus been released. Leaves are affected from both sides, resulting in obvious spots or large blemishes with a silvery shimmer (Photo 371) – in high populations this situation may contribute to overall colouration and even large-scale deleafing of grapevines. Although berries are affected early in the growing season – during set especially – feeding damage is clearly recognisable as a hardened/corky discolouration (especially on the uppermost part of the fully grown berry, around the pedicel) (Photo 372).

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