Symptoms
Lack of magnesium can result in disorders such as bunch stem necrosis. It starts as a hollow necrosis on the stalk of the berries, later the grape skin breaks down and pulp becomes watery.
The disease is also known as Water Berry, Stiellähme, Shanking, Palo negro, Dessèchement de la Rafle).
Reasons
Magnesium deficiency (bunch stem necrosis)
High applications of K or ammonium can induce Mg deficiency symptoms even on soils that contain enough Mg.