Definition - What does Black Rot mean?
Black rot is disease of the grape fruits caused by the fungus Guignardia bidwellii that grows during warm, wet climates in the spring and summer months. The disease affects most parts of the vine - the shoots, leaves, fruit, stems and tendrils, but the most extensive damage is on the fruit. Without proper treatment or prevention, Black Rot can destroy the whole crop and even future crops if the fungus is not eradicated properly.
WineFrog explains Black Rot
The first symptom of black rot is the appearance of small, tan/reddish brown angular or circular spots on the younger leaves. Following the appearance on leaves, a small spot will emerge on the fruit that are circular and white/tan in color. These spots develop while the fruit and leaves are still green and eventually turn them from green to brown. The spots can grow very rapidly and cover the fruit quickly, on the leaves they can form lesions that mature into the fungal reproductive formations. Once there are reddish brown rings present, the berries will die, dry up and fall to the ground where they will rot and turn black in color.
The most effective form of Black Rot prevention is genetic resistance, picking grapes that can fight off black rot. However, Black Rot is a major disease threat to the vitis vinifera and grows as a cause of improper pruning and sanitation. It is important to remove old plant tissue, prune during the dormant season and reduce vineyard moisture with canopy control and shoot positioning. There are some fungicides made for Black Rot prevention and applied just before bloom or just after. Caution should be used when applying fungicides and should be avoided or sprayed in low quantities during wet weather conditions.