Eutypa Dieback

Eutypa dieback, caused by the fungus Eutypa lata, is the new name for the canker- and shoot- dieback phase of what was once known as dead-arm. The name "Dead-arm" should be dropped.

Symptoms

The earliest symptom to develop is a canker that generally forms around pruning wounds in older wood of the main trunk (Figure 71). These cankers usually are difficult to see because they are covered with bark. One indication of a canker is a flattened area on the trunk. Removal of bark over the canker reveals a sharply defined region of darkened or discolored wood bordered by white, healthy wood. Cankers may be up to 3 feet long and may extend below the soil line. When the trunk is cut in cross-section, the canker appears as darkened or discolored wood extending in a wedge shape to the center of the trunk.

Figure 71: Eutypa canker on grape trunk.

The most striking and obvious symptoms of Eutypa dieback are the leaf and shoot symptoms (Figure 72), which may not develop for 2 to 4 years after the vine was first infected. These symptoms are most obvious in spring, when healthy shoots are 12 to 24 inches long. Spring shoot growth on diseased canes is weak and stunted above the cankered area. Leaves are at first smaller than normal, cupped, distorted, and yellow. These leaf and shoot symptoms may not be as obvious later in the season (mid-July). Leaf and shoot symptoms are more pronounced each year until the affected portion of the vine finally dies.

Figure 72: Eutypa symptoms on grape leaves.

Eutypa Dieback Disease Cycle (Figure 73)
The fungus survives in infected trunks for long periods, whether as part of the in-place vine or as old, dead grape wood in the vineyard. The fungus is generally present in older wood, such as vine trunks, but generally not in younger wood, such as 1- or 2-year-old prunings. The fungus eventually produces reproductive structures (perithecia) on the surface of infected wood. Spores (ascospores) are produced in these structures and discharged into the air. Ascospore discharge is initiated by the presence of free water (rainfall or snow melt). Most spores appear to be released during winter or early spring; few are released during the summer. Unfortunately, most spores are released at about the same time pruning is being conducted. Air currents can carry the ascospores long distances to fresh wounds on the trunk. Pruning wounds are by far the most important points of infection. The ascospores germinate when they contact the newly cut wood, and a new infection is initiated. Stunted shoots and small, cupped leaves appear 2 to 4 years after infection. After approximately 5 years, the fungus produces perithecia and ascospores in the dead wood on cankers.

Figure 73: Eutypa dieback disease cycle. We wish to thank the New York State Agriculture Experiment Station for the use of this figure. Figure taken from Grape IPM Disease Identification Sheet No. 1.

Control of Eutypa Dieback

The primary control method is removal of infected trunks from the vineyard. The vine must be cut off below the cankered or discolored wood. If the canker extends below the soil line, the entire vine must be removed. If the canker does not go below the soil line, the stump can be left and a new trunk formed. The best time to identify and remove infected vines is in early spring (May and June) when leaf and shoot symptoms are most obvious. In addition, large wounds are less susceptible to infection at this time of year, and fewer ascospores are present to cause reinfection. If trunks cannot be removed in the spring, they should be marked for easy identification and removal later in the growing season.

Sanitation is critical. All wood (especially trunks and stumps) from infected plants must be removed from the vineyard and destroyed (either buried or burned) as soon as possible. An old infected stump or trunk lying on the ground may continue to produce spores for several years.

The double trunk system of training, where each trunk is pruned to carry half the number of buds, may help reduce crop loss caused by Eutypa dieback. If a diseased trunk must be removed, the remaining trunk can be pruned to leave the full number of buds until a new second trunk can be established.

Fungicide recommendations currently are not available for control of this disease.