phomopsis, may refer to either phomopsis cane and leaf spot or phomopsis dieback. Both are caused by the fungus Phomopsis viticola but the symptons are quite different.
Phomopsis cane and leaf spot, also known as Diaporthe, excoriose, and dead arm, occurs in most of the world’s viticultural regions and is particularly severe in those characterized by a cool and wet spring followed by humid, temperate weather through the growing season. Under these conditions, the disease may cause crop losses of up to 30%. The fungus can infect all green parts of the grapevine, causing black lesions at the base of grape shoots, leaf petioles, and bunch stems; bleached patches on winter canes; the death of affected fruit buds; stunted shoots; small black spots with yellow halos on deformed leaves, and rot on infected berries. Infected wood appears bleached during the dormant season and fruiting structures of the fungi (pycnidia) can be seen embedded in the bark. Although this disease poses the greatest threat in early spring, control measures to protect the fruit may continue into the summer in some regions. Because the fungus colonizes old wood, cane pruning and hand harvesting reduce pressure from this disease. Wine grape varieties such as Cabernet Sauvignon, Chardonnay, Merlot, and Syrah are less susceptible than some table grapes. However, grenache is one of the most susceptible.