This plant disease is caused by a fungus (Eutypa armeniacae). The fungus survives the winter in trunk and branch cankers. Fungal spores that form in the cankers are carried by splashing water
to pruning wounds, where they infect the plant. Infection causes the formation of cankers that reduce the flow of water and nutrients through the trunk and branches. The portion of the plant above the canker will weaken and may eventually die.
Prune out and destroy infected branches and canes. Late-winter pruning reduces the probability of infection. Make the pruning cut at least 6 inches below the canker and any discolored wood. If cankers are present on the trunk, remove and destroy the entire plant, cutting the trunk below the lowest canker but above the bud union. Maintain 2 to 4 suckers on the trunk. The plant will not produce grapes this year but will yield a normal crop next year.