Long-lasting and strong sunlight during summer in high-pressure weather conditions compounded by soil dryness may cause leaves and berries of vines to wither. Young grapes are particularly vulnerable if they were previously shaded by leaves and are not yet accustomed to strong UV radiation. The grapes turn pink first and then brown before turning inedible an dry like raisins. Some grape varieties are more sensitive than others. When the weather is too hot, be careful not defoliating too much in the grape zone or leave it altogether. The grapes will color even when shaded!