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

PART 3

BACTERIAL DISEASES 3

B ecause grape cultivars – as in die case of fungal diseases – differ from one another regarding their susceptibility/resistance to important bacterial diseases (Perold, 1927; Du Plessis, 1947; Matthee et al., 1970; Marais, 1981), the cardinal role that moisture and termperature play as climate parameters in the occurrence thereof must also be thoroughly taken into account here. Besides cultivar and region choices, decisions on slope, location, vine spacing, canopy and irrigation systems as well as canopy management practices are of great importance – arising from the positive impact on the entry and spread of bacterial diseases within vineyards, resulting from practices which could/may contribute to them. Consistent with fungal diseases, abnormalities related to this will also in must cases reflect local damage to the relevant organs, with in nearly all cases specific observable lesions to organ surfaces. Should bacterial diseases thus occur to such an extent that the visual impression thereof is associated with specific abnormalities, serious/lasting damage has already been caused – a situation which is exacerbated by the inability of strategies/ remedies to destroy bacteria in established material (as with bacterial blight) or in the soil (as with crown gall). It goes without saying that all control practices (whether chemical or biological) should focus on a continuous preventative base and that the use of certified propagation material during establishment should be at all times considered the highest priority to combat the spread of these diseases.

94 • A Guide to Grapevine Abnormalities in South Africa