The precipitation that occurs in connection with thunderstorms in the form of ice balls or clumps with a diameter of five to 50 millimetres (rarely even larger) arises in rapidly rising, moist air currents. Depending on their size, the hailstones can perforate or completely destroy the leaves and damage the shoot tips, which in extreme cases can lead to complete defoliation. If large parts of the foliage and thus the assimilation area are affected, the growth and development of the vine is impaired, which can also have an impact on the next harvest. A possible consequential damage caused by defoliation is, for example, grape wilt caused by sunburn.
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