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

GRAPEVINE PESTS Birds, bagworms, rodents, white ants, dassies, antelopes and moths/butterflies 5.7 Birds Abnormalities emanating from bird damage are very characteristic and are usually associated with typical, visually detectable pecking and feeding patterns in ripening/ripe grapes. A common tendency among the smaller bird species is to peck holes in individual berries before eating the complete or partial contents thereof – thereby creating easy ingress options for a wide variety of secondary rotting organisms (Photos 373 & 374). In the case of bigger birds (starlings for example) entire berries are removed – a situation which may contribute, depending on the area, cultivar and vineyard location, to considerable/total crop losses (Photos 375 & 376). Furthermore indirect bird damage, as associated with the potential spreading of mealybug and leafroll, should enjoy high priority on an ongoing basis. Bagworms Although the sporadic incidence of bagworms (in SA also known as ‘broekmanwurms’) is a well-known phenomenon, in the Stellenbosch and Agter-Paarl areas especially, large-scale damage associated with the feeding activities thereof is not considered to be a cause for concern. The visual incidence of bagworms – the larvae of which are housed in artistically made ‘cocoons’ (consisting of a sturdy bag made of silk threads around the body, to which has been attached twigs or blades of grass that have been nibbled short) – make it utterly and positively recognisable as a pest phenomenon (Photo 377). During the active stages one often finds that bagworms hang from grapevine leaves in their twig-‘cocoons’, with protruding head and forequarters so as to eat holes in the leaves (Photo 378). Although no serious damage to vineyards has ever been reported, one should allow for the possibility of epidemic outbreaks (especially where it may occur in conjunction with other pests) – and it is best to keep abreast of identification procedures. Rodents Feeding damage by rodents such as mice is mainly associated with ring-barking activities in varying degrees of intensity on the trunks, both above and below the surface of the soil, of established grapevines. In such instances it has been found that large parts of the bark and phloem and even around the trunks are eaten/stripped, thereby exposing the cambium (Photo 379). Although such harmful interventions usually occur below the surface, in which case excessive callus and root formation is initiated in an attempt to keep the grapevines going (Photo 380), it has been found that phloem is unable to bridge large parts of the ring-barking wounds above the soil surface – which may even extend to positions above the graft unions (Photos 381 & 382). It goes without saying that normal physiological processes in affected grapevines are compromised to the extent that in addition to deterioration, complete dieback may be the fate of younger grapevines especially. In addition to the characteristic feeding patterns of mice that are visually evident, the incidence

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