The fungus causing this disease has a wide host range, which includes at least 80 species in 27 botanical families. Most of its hosts are tree species that are common in natural forests.
The earliest symptoms of the disease are cankers formed around pruning wounds. The cankers are hard to detect since they are concealed by old, dead bark, which can become somewhat flattened. A cross-section of the infected area might 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 the infection of the pruning wound. As new shoots develop on the trunk or arms above the cankered area, vine growth appears stunted and the internodes become shortened. Symptoms are not readily visible until late spring because affected shoots usually are covered up by healthy shoots. Infected leaves are small, yellow, and crinkled. Symptoms on the 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 can have a mixture of both large and small berries.
The disease is caused by the fungus Eutypa lata. This disease is entirely different from that responsible for phomopsis cane, leaf spot, and fruit rot. Rain is necessary for the spread of this disease, and infections occur on freshly made wounds. The susceptibility of wounds decreases as they become older (2 to 4 weeks after pruning). The disease is slow to develop on grapes and usually is not seen until the third or fourth season. By this time, a canker usually is present, along with symptomatic foliage. Several more years might elapse before the diseased arm or trunk is killed.
No grape varieties are known to be immune to this disease. Also, none of the chemicals routinely used to control other grape diseases provides protection against this fungus. Some evidence indicates that the manual treatment of individual wounds with benomyl at the time of pruning can provide a barrier against the fungus and prevent it from invading the wounds. It is suggested to treat all wounds in wood 2 years of age or older, especially large wounds. Sanitation practices also will help 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. 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.
This publication is available in alternative media on request.