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

PART 6

ABIOTIC ABNORMALITIES 6

A biotic abnormalities are associated with damage as chiefly caused by environmental conditions. Globally considered, such harmful interventions can be exercised in diverse formats and varying grades of intensity – reflecting that serious conditions can contribute to permanent damage to or even destruction of vines, while the rate of impact in more moderate conditions should maintain a lower profile. Although individual phenomena are chiefly associated with specific/demarcated causal factors, it is not the case with among others drought, waterlogging and salinity, where all three cases can be ascribed to a common cause – as represented by the initiation of water shortages in surface organs of affected vines. Naturally it is important to make a distinction between water shortages resulting from long term/continual subjection of vines to the abovementioned conditions and those which may occur temporarily – even in cases of carefully scheduled irrigation. In respect of the latter a recent publication, in which the visual appearance of temporary water shortages at shoot tips, leaves and tendrils is richly illustrated, can be considered valuable to practice-orientated utilisation (Schutte, 2012). In contrast with drought, waterlogging and salinity, the incidence of bunch stem necrosis and the growth arrestment phenomenon (GAP) – which occurs chiefly in table grapes with the latter almost exclusively limited to the Lower Orange River area – is not associated with a common cause, but various and diverse situations were revealed to be important drivers in terms of the occurrence(s) of these complex physiological phenomena (Van der Merwe, 1994; Van der Westhuizen et al., 2001; Myburgh, 2008; Laker & Conradie, unpublished; and others). Arising from this research, investigations and observations over many years, a basic awareness of specific factors involved (in single or combined format) could be formulated, namely: growth regulator imbalances; climate; nutrition; soil; rootstocks; scions as well as vigour/potential crop yield with the former, and dormancy physiology; climate; soil; irrigation; rootstocks and fungal diseases (early defoliation) in the latter. Viewed generally and based on the fact that some abnormalities in this category may appear to be similar to those of diseases, pests and even physiological problem situations, and additionally in nearly all cases contribute to a lesser or greater extent to economic losses in the short and/or longer term, the implimentation of preventative as well as corrective actions/measures – as based on extensive expert knowledge/advice – cannot be over- emphasized. Thus it may contribute to the scrupulous/judicious adherence to specific guidelines laid down in the abovementioned regard, and could entail an important applicability over the total spectrum of practices related to sustainable/profitable viticulture in the different regions.

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