Leafroll is a viral disease of grapevines in which the virus infection seals off the leaf petiole (stem) so that the sugars produced by the leaf through photosynthesis cannot be transported back into the vine. The leaves tend to curl downwards at the edges as the sugar accumulates. The leaf, in an effort to get rid of a problem, uses it to make red anthocyanin pigment and the leaf is seen to turn red as well as appearing rolled. Vines infected by these viruses have difficulty in ripening their fruit because much of the sugar the vine produces cannot be used by the vine where it needs it— in the fruit. Leafroll may not be a serious problem in varieties which ripen early but are grown in climates which provide a longer than needed season. But when the opposite is true, where the variety just barely ripens under normal conditions, then the infection by leafroll virus causes the crop never to fully ripen, with disastrous results to resulting wine quality. (Wine/Other)