Eutypa Dieback of grapes is caused by the fungus Eutypa lata. The fungus survives in diseased wood and produces perithecia in old, affected host tissue under conditions of high moisture. Ascospores are discharged from perithecia soon after rainfall. This is the only known means of dispersal and infection. Infection occurs when airborne fungal spores contact fresh pruning wounds during or immediately following rain. Pruning wounds become resistant to infection about 2 to 4 weeks after pruning, and about a week longer early in the dormant season than later in the dormant season.
Eutypa dieback is not generally visible in vines younger than 5 to 6 years old and is seen most frequently in vineyards established for 10 or more years. Incidence can be especially high in older vineyards where large pruning wounds were made to alter the training system. Moderately infected vineyards can lose 19 to 50% of yield, severely affected vineyards 62 to 94%. The fungus can attack many other hosts including many Prunus sp. (peaches, plums, cherries, etc.), apples, pears and walnuts.
Symptoms are best seen in spring when healthy grapevine shoots are 10 to 15 inches long. Eutypa dieback delays shoot emergence and causes chlorosis (yellowing), stunting, tattering, and sometimes cupping of leaves. Some or all blossoms may drop from flower clusters. Later in the season, 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. Symptoms may not appear on diseased vines for more than 3 years after infection.
Symptoms in the wood are characterized by darkened cankers that develop in the vascular tissue. Eutypa cankers are always associated with old pruning wounds. The cankers are wedge shaped (like a pie chart) in cross-cuts of affected branches, 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. Eutypa cankers expand lengthwise in both directions from the wound and girdle and kill arms or trunks of infected vines in 5 to 10 years.
Eliminate all infected wood of grape, Prunus sp., or other known hosts to reduce the risk of this disease. Cut out and remove dead arms and cordons from the vineyard. Completely remove all cankers, pruning below the canker on the vine or trunks until no darkened canker tissue remains. If the canker is below ground, remove and replace the vine.
Dormant pruning can be done directly after a rain when the risk for infection is lowest as the atmospheric spore load has been washed out temporarily (or is at its ebb). Prune late in dormant season to promote rapid healing of wounds. Avoid large pruning cuts whenever possible.
Treatment of fresh, large pruning wounds could offer some disease control, but currently there are no chemicals labeled for control of this disease. Notes: Although Dreft baby diaper detergent at 30% wt/vol is excellent, it can not be used for this purpose since it does not have an EPA label.
Pscheidt, J.W. 2002. Eutypa Dieback. Online Guide to Plant Disease Control. Oregon State University.
Grape Eutypa Dieback. University of California IPM Pest Management Guidelines.