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Minimising bunch stem necrosis in wine grapes
Bunch stem necrosis (waterberry) in wine grape affects fruit set and fruit ripening. It can occur around the bloom, in which case it is called early bunch stem necrosis, at veraison or later. The occurrence of it is associated to weather conditions and crop nutrition.
During bloom, the symptoms of bunch stem necrosis begins as the pedicel elongates. It can become necrotic, resulting in the dropping of the flower buds. Later, entire sections of the inflorescence can shrivel and die, and may or may not drop off. The symptoms appear as necrotic patches on the rachis or peducle. As a result, supply of water and nutrients are limited, leading to wine grape berries with less sugar, remain sour and eventually shrivel.
Crop Nutrition and Bunch Stem Necrosis in Wine Grape
Magnesium
Bunch stem necrosis is often associated with a magnesium deficiency and the imbalance of magnesium and nitrogen. Research suggests that low levels of sugars in storage organs and fruit lead to nitrate accumulation, particularly during cold weather during maturation. Two to three foliar applications of magnesium starting just before veraison minimise the problem.
