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

Leafhoppers According to available literature, the local incidence of leafhoppers dates back to the 1978/79 growing season, when they suddenly multiplied to epidemic numbers in grapevines in the vicinity of Tulbagh. Ever since then, their occurrence has been widespread in practically all the viticultural regions – with the possibility of causing serious damage to affected grapevines. Leafhoppers have sucking mouthparts and feeding activities consist of extracting plant sap from the vascular bundles on the underside of leaves (Photo 354) – with the result that: (i) phytoplasmas associated with yellowing diseases may be carried to the phloem and (ii) a brown discolouration starts from the outer edges of the leaves. Initially the discoloured areas look leathery, but they dry out systematically to become brittle – a situation that may eventually contribute to total desiccation and subsequent loss of leaves in grapevines (Photo 355). Obviously the loss of leaves, whether this occurs before, during or shortly after the harvest, is extremely detrimental, especially in terms of the ripening of shoots, accumulation of reserves, as well as sunburn damage to exposed grapes. Boll-worm Boll-worm, a well-known phenomenon in a variety of crops, is considered a sporadic pest in grapevines, which may cause serious damage during conditions that are conducive to multiplication to epidemic numbers. According to available literature, up to four generations may occur per growing season, which in itself indicates that it has the ability to multiply rapidly and assume plague numbers. Although the colour of larvae ranges from green to brown, a pale yellow stripe along the sides serves as a characteristic aid in terms of appropriate identification procedures. Damage is mostly wrought early in the growing season, in which case feeding activities are associated with eating damage (causing mostly holes) on leaves, shoots and berries, while even flowers, or parts thereof, are also appetising to immature and fully grown larvae (Photos 356 - 360). Leaf roller caterpillars Although leaf roller caterpillars (Photos 361 - 366) – sometimes known in the vernacular as ‘cock’s comb’ or ‘cock’s crow’ – occur in all local wine-growing areas, the sporadic multiplication thereof to epidemic plague numbers is considered exceptional. When conditions are favourable, however, and following the hatching of moth-laid eggs on leaves, serious feeding damage may be caused by actively feeding/rapidly growing larvae – a situation where large parts of leaves are eaten to such an extent that grapevines may lose their leaves altogether (especially in nurseries). Although two examples (light brown and green) occur locally, larvae are easily recognised by the characteristic protrusions (horns) on their hind parts, as well as large, brightly coloured spots just behind the head. Positive identification procedures furthermore rely on: (i) characteristic feeding patterns – leaves GRAPEVINE PESTS Leafhoppers, boll-worm, leaf roller caterpillars, spring beetles, wilting beetles and thrips 5.6

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