Cause The fungi Eutypa lata var. lata, has been found in all areas. In addtion E. laevata has been found in Washington and E. leptoplaca has been recovered in Oregon. Up to 24 species in various genera are reported to cause this disease but E. lata is the most common. The disease is prevalent on 'Concord' vines in eastern Washington but also on wine grapes throughout the PNW. Symptoms are generally not noticed until year 8 when disease incidence may be about 10% but yield losses are, to this point, minor. Incidence is especially high in older vineyards where large pruning wounds were made to alter the training system. A brief preliminary survey found incidence high in non-irrigated vineyards containing old vines in southern Oregon. Moderately infected vineyards can lose 19% to 50% of yield; severely affected vineyards 62% to 94%. The disease has been observed frequently on wine grapes in the Willamette Valley of Oregon. Also, the fungus can infect cherry trees, which are heavily planted within many of the same areas and can act as a reservoir of inoculum. The fungus can attack other hosts including many orchard crops such as Prunus spp., apples, pears, and walnuts and plants gown as ornamentals, or in riparian areas, such as big leaf maple, and willow.
E. leptoplaca, has been found in vineyards of northern California. Isolates of this fungus collected from California bay laurel and bigleaf maple trees adjacent to vineyards were found to cause disease in grapevines when inoculated.
Ascospores are released from perithecia in infected wood during rain events and may be carried long distances on air currents. Ascospores are discharged after 2 hours of rainfall and are released for 36 hours at which time perithecia are depleted of available ascospores. New mature ascospore are available for release after 12 more days. Infection occurs when airborne ascospores contact fresh pruning wounds during or immediately following rain. Pruning wounds become resistant to infection about 2 to 4 weeks after pruning. In general, pruning wounds made early in the dormant period are much more susceptible than wounds made late in the dormant period. Although water stressed vines are more susceptible to infection, subsequent colonization of the vine is more limited.
Cultivar susceptibility is dependent on various evaluation systems and high variability. One study found the number of inoculated spurs to be 72% for Grenache and 47% for Pinot Noir but the rate of stain spread was significantly higher for Pinot Noir. Cabernet Sauvignon was similar to Pinot Noir and Merlot had the least number of spurs infected and lowest rate of stain spread. Differences in susceptibility may also be due to reaction of the foliage to translocated toxins which is only produced by one species, E. lata.
Symptoms Stunted spring shoot growth, yellowed and cupped newly emerged leaves, shed blossom clusters, vascular discoloration, and cankers in stems associated with old pruning wounds. In advanced stages, part or all of a vine dies. Symptoms are best seen in spring when healthy grapevine shoots are 10 to 15 inches long. Later in the season, affected shoots are 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. Experience in Australia has shown that foliar symptoms may be variable from year to year, especially in 'Shiraz'. 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.
Cankers expand lengthwise in both directions from the wound and girdle and kill cordons or trunks of infected vines in 5 to 10 years. Removal of the bark will expose the extent of the canker. When cut in cross section, cankers may show wedge-shaped discoloration where the widest part is near the outside of the trunk or cordon and the thinnest part near the center. This symptom can be produced by several other grapevine trunk disease fungi such as Botryosphaeria.
Cultural control Preventative tactics are more effective when started early in the life of a vineyard.
- In spring, when symptoms are evident, mark diseased vines for future removal during dry weather.
- Prune hard well below the visible canker. Remove diseased wood 4 to 6 inches below discolored vascular tissue, and train a new, healthy shoot into position.
- Use a multiple trunk training system, which will allow for trunk replacement without losing an entire vine.
- If the canker is below ground, remove and replace the vine.
- Avoid large pruning cuts when possible; avoid pruning during and before wet weather. Pruning later in the dormant period has been useful in California but not British Columbia.
- When making large cuts during wet weather, leave a stub several inches long to be pruned off later during dry weather. Sometimes referred to as delayed or double pruning or prepruning.
- Remove and destroy all large trunk or cordon pieces from the vineyard.
- Pruning wound treatments with sealants or paints have been effective when used within 24 hours of the pruning cut. These products include B-Lock, Spur Shield, or Vitiseal. See labels for details.
Chemical control Useful when pruning a new planting or retraining vines and making large trunk or cordon cuts. Tank mixes with products from different FRAC groups has also been helpful.
- Mettle 125 ME at 5 fl oz/25 to 50 gal water/A as a spray directed onto cuts within 24 hr of pruning. A second spray 2 weeks later is recommended. Do not use more than 10 oz/A/year for this and in-season powdery mildew treatments. Group 3 fungicide. 12-hr reentry.
- Rally 40 WSP at 5 oz/50 gal water as a spray directed onto cuts within 24 hr of pruning. A second spray 2 weeks later is recommended. Do not use more than 24 oz/A/year for this and in-season powdery mildew treatments. Group 3 fungicide. 24-hr reentry.
- Topsin 4.5 FL at 30 fl oz/A as a spray directed onto cuts within 24 hr of pruning. A second spray 2 weeks later is recommended. Topsin 4.5 FL may also be used at 4 fl oz/1 gal water and applied as a paint to cut or pruned surfaces. Use when rain is not expected after application. Group 1 fungicide. 2-day reentry.
- Topsin M WSB at 1.5 lb/50 gal water as a spray directed onto cuts within 24 hr of pruning. A second spray 2 weeks later is recommended. Topsin M WSB may also be used at 3.2 oz/1 gal water and applied as a paint to cut or pruned surfaces. Use when rain is not expected after application. Oregon only SLN OR-150009A. Group 1 fungicide. 2-day reentry.
Biological control Use in conjunction with cultural control tactics such as thorough sanitation. Trichoderma sp. have been shown to help protect pruning wounds, basal ends of propagation material, and graft unions before infection. Use within 24 hr of pruning.
- Bio-Tam 2.0 (Trichoderma asperellum and T. gamsii) at 1 lb/A in 25 to 50 gal water plus a dye. May take a few weeks after application to be effective. 4-hr reentry. O
- Serenade ASO (Bacillus subtilis strain QST 713) can be used as a 2% to 5% solution applied to pruning wounds. Active ingredient is a small protein. Efficacy in the Pacific Northwest is unknown. 4-hr reentry. H O
References Hillis, V., Lubell, M., Kaplan, J., and Baumgartner, K. 2017. Preventative disease management and grower decision making: A case study of California wine-grape growers. Phytopathology 107:704-710.
Gramaje, D., Úrbez-Torres, J.R., and Sosnowski, M.R. 2018. Managing grapevine trunk diseases with respect to etiology and epidemiology: current strategies and future prospects. Plant Disease 102:12-39.
Mondello, V., Songy, A., Battiston, E., Pinto, C., Coppin, C., Trotel-Aziz, P., Clément, C., Mugnai, L., and Fontaine, F. 2018. Grapevine trunk diseases: A review of fifteen years of trials for their control with chemicals and biocontrol agents. Plant Disease 102:1189-1217.