bunchstem necrosis or BSN, physiological condition which causes grape bunchstems to shrivel and die during ripening. This condition is also known as water berry in California, shanking in New Zealand, Stiellähme in Germany, and dessèchement de la rafle in French. Affected berries do not ripen properly and shrivel on the bunch, although it is rare for all berries to be affected. cabernet sauvignon vines are particularly prone to this disorder. Affected berries have lower sugars, anthocyanins, and fatty acids, but higher acidity. The cause is unknown, but factors associated with the condition are vigorous shoot growth, the weather at flowering, and levels of magnesium, calcium, and ammonium in the plant tissue. Yield can be severely reduced, especially with mechanical harvesting, as affected berries fall off. Wines can taste bitter and are poorly coloured. There is no widely accepted control, although magnesium sprays at veraison have sometimes reduced the problem. A similar disorder affects inflorescences at flowering and has been termed early bunchstem necrosis, or ‘inflorescence necrosis’.
