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

Root formation problems (3); withered shoot growth (4); vascular tissue problems (5). FUNGAL DISEASES Fungal diseases associated with wood and root rotting/dieback 2.7.2

Esca dieback Esca – its presence is associated with various fungi in the trunk disease complex – occurs in all the winegrowing regions, especially in older grapevines. Although characteristic traits of infected grapevines are not necessarily visually apparent each year, internal rotting following initial infection continues unabated and eventually causes sudden (apoplexy) or more gradual (esca) dieback of grapevines, whether partially or entirely (Photos 119, 120, 121, 122 & 123). In grapevines that used to display healthy growth, the first visual observations of esca are characterised by typical discolouration patterns on basal leaves, in which case uneven yellow (white grape cultivars) and red (red grape cultivars) spots develop between main veins and later become merged. Subsequently these parts turn reddish brown, their appearance becoming typically finger-like, with the dead brown tissue in leaves looking shredded (Photo 124). Obviously this leaf discolouration pattern does not occur in apoplexy and one finds that shoots with leaves wilting from the tips, are followed by sudden drying out and dieback. Characteristic of the esca/apoplexy-complex is the occurrence of black spots (measles) on developing berries (Photo 125). Such berries, which look purplish in white grape cultivars, shrivel and dry out to assume a raisin-like appearance (Photo 126). In infected grapevines in this category, soft-wood rotting often occurs near the soil surface (Photos 127 & 128). Internally rotten parts appear yellowish with whitish- yellow discolourations of the soft parts of the wood (Photo 129). Obviously internal rotting as a result of esca can assume various patterns (Photos 130 & 131) and therefore it is recommended that expert advice be obtained for accurate identification procedures. Black goo (Petri disease) and black foot dieback / rotting Although dieback / rotting associated with black goo (Petri disease) and black foot may occur in nursery vines as well as older vines, the younger vines in particular – mostly during the years following establishment – display specific behavioural patterns as a result of the above-mentioned situations. Both phenomena are associated with the trunk disease complex, in which case initial infections display a close relationship to wounding of material, which is inevitable from propagation and grafting onwards. Visually detectable characteristics of Petri disease and black foot – as represented by delayed or no bud burst, yellowing of canopies, dwarfed shoot growth and overall dieback – are mainly associated with abnormalities of the vascular tissue (browning, rotting and blocking). Obviously such situations could result in serious hampering/arrest of normal sap flow, thereby contributing

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