Dead arm

The most recognizable symptom is abnormal, reduced, and deformed shootgrowth and is best seen in spring, when shoots are 10 to 15 inches long. Leaves on shoots may be malformed, cupped and yellow (chlorotic). Affected shoots may shed blossom clusters or have non-uniform berry sizes. Sunken areas (cankers) typically form on cordons or trunks near affected shoots, and are most often associated with large pruning wounds. Cankers expand lengthwise in both directions from the wound and girdle and kill arms or trunks of infected vines in 5 to 10 years. Later in the season, affected shoots will be stunted, and leaves become tattered and scorched. Clusters on infected shoots are poorly developed and often wither and drop. Infected vine foliage may be covered and masked by the foliage of healthy grapevines. It is also common to find one side of a vine dead or with disease symptoms and the other side apparently healthy. A cross section of the cut canker will show a wedge-shaped, dead, discolored portion of the wood, but the wedge of dead wood alone is not conclusive diagnostic evidence of the disease. Other factors, including freeze injury, can cause identical wedge-shaped regions of dead wood. Symptom development can take a long time to occur after infection (two or more growing seasons), due to the slow growing nature of the fungus.