Investigation of dying back of young vines along the Lower Orange River Area as associated with delayed budding and/or growth
Volschenk, C G
The dying back of young vines, delayed budding and retarded growth of young and fullbearing vines is a common phenomenon in the Lower Orange River Area which has huge financial implications. Green house studies were conducted in order to understand the phenomenon better. A good relation between root development and vegetative growth was found for vines cultivated in nutrient solutions at different temperatures. High temperatures increased root development and growth which, in turn resulted in higher vegetative growth, while low temperatures prevented or reduced root development and growth resulting in poor vegetative growth. It seems that a minimum temperature of 15°C is required at which root development and growth, although slowly, occurs to prevent retarded vegetative growth.
The average soil temperature on the experiment farm during budding is also about 15°C and a decrease in soil temperature due to a decrease in air temperature and irrigation, could prevent root development and growth and therefore increase the risk of growth arrestment phenomenon (GAP). During the first four weeks the starch content of the scion and rootstock of vines cultivated at higher nutrient solution temperatures was reduced by ±50%, being utilized for budding, vegetative growth and root formation. Low carbohydrate reserves in vines could also reduce budding, vegetative growth and root formation and result in GAP.
Luxurious nitrogen fertilization of 300 kgN/ha/year initially, and 500 kgN/ha/year later during the investigation, increased the nitrate content for the soil, the nitrogen content of the canes, leaf blades and petioles and it increased vegetative growth. This did not increase the occurrence of GAP in this specific vineyard. An investigation of another vineyard, however, revealed that luxurious nitrogen fertilization could increase GAP. Climatological studies indicated that, during years in which severe frost occurred during autumn, GAP is likely to occur during spring as a result of insufficient carbohydrate accumulation. GAP is a common phenomenon in the Lower Orange River Area and producers must accept that it will occur sporadically. There is no quick cure for this problem, but vineyard selection, careful nitrogen fertilization, reduction in vegetative growth during autumn and frost control could reduce the risk of GAP.
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