Eutypa dieback is the name for the trunk and arm phase of what was once known as the "dead arm" disease. It is one of the most destructive diseases on woody tissue of grapes. The fungus causing this disease has a wide host range that includes at least 80 species in 27 botanical families. Most of its hosts are tree species that are usually common in natural forests.

Symptoms

The earliest symptoms of the disease are cankers formed around pruning wounds. The cankers are hard to detect as they are concealed by old, dead bark, which may become somewhat flattened. A cross section of the infected area may show a wedge-shaped area of darkened wood coming to a point in the center of the trunk. Symptoms of Eutypa dieback are apparent after the canker has become well established, perhaps 2 to 4 years after infection of the pruning wound.

As new shoots develop on the trunk or arms above the cankered area, growth appears stunted and the internodes shortened. Symptoms are not readily seen until late spring because affected shoots are usually covered up by healthy shoots. Infected leaves are small, yellow, and crinkled. Symptoms on foliage of diseased arms become more extensive each year until eventually the diseased arm fails to produce shoots in the spring. Clusters on affected shoots may have a mixture of both large and small berries.

Symptoms of Eutypa on leaves and wood

Disease Cycle

The disease is caused by the fungus Eutypa lata. This disease is entirely different from that responsible for Phomopsis cane blight, leaf spot, and fruit rot. In winter, during rainfall or snow melt, fungal spores are released from fruiting structures on dead infected wood. Spores are dispersed by the wind and infection occurs when they enter fresh pruning wounds. Rain is necessary for the spread of this disease. The susceptibility of wounds decreases as they become older (2 to 4 weeks after pruning). The disease is slow to develop on grapes and is usually not seen until the third or fourth season. By this time, a canker is usually observed as well as symptomatic foliage. The vine deterioration continues until the trunk or arm is finally killed usually requiring several more years.

Disease Management

No grape cultivars are known to be immune to this disease. Also, none of the chemicals routinely used to control other grape diseases provide protection against this fungus. Sanitation practices are suggested to control this fungus. Since the fungus survives in vines remaining on the tree or as prunings in the vineyard, affected vines should be pruned when leaf symptoms appear. Infected arms and trunks should be removed in late spring when foliar symptoms are noticeable and wounds are less susceptible. Pruning should be far enough below the canker that healthy wood is evident. Any infected wood or stumps should be removed from the vineyard and burned. Single-trunk vines should be cut off at the ground line; double-trunk vines should be cut off at the junction of the second trunk. Affected prunings must be removed from the vineyard immediately and destroyed. One or more suckers can be retained for vine renewal.