Cause Diaporthe ampelina (formerly Phomopsis viticola), a fungus. The disease has been not been found frequently in vineyards west of the Cascade Range and rarely in Oregon. The fungus overwinters in last year's cane growth. Fruiting bodies of the fungus (pycnidia) develop in the periderm and produce many spores in the spring. These spores are exuded during rain events when the bark is wet. Spores are then rain splashed to developing shoots. Warm temperatures during long wet periods favor infection. About 10 hours of shoot wetness is required for light infections at 50°F. Young, rapidly growing tissues are most susceptible. Cluster rachis lesions are associated with the most consistent cause of economic loss. This same fungus has been found infrequently as a trunk pathogen but the connection between cane symptoms and grapevine trunk disease is unknown. Vineyards severely infected with cane and leaf spot also had a high incidence of vine dieback.
The more susceptible cultivars include Grenache, Flame Tokay, and Thompson Seedless. Under high inoculum cultivars Colombard, Cabernet Sauvignon, and Petit Verdot may show symptoms as well. Other cultivars are less susceptible.
Symptoms In the dormant season, infected canes may become bleached, and numerous black fruiting bodies (pycnidia) may develop all along the cane's basal region. This is the most common symptom in the Pacific Northwest; however, other nonpathogenic fungi can cause similar cane bleaching. Susceptible cultivars may show elongate lesions on the cane's basal internodes. Small leaf spots also can occur early in leaf development, which can severely crinkle or misshape the leaf. Leaf petioles and cluster rachises also can develop lesions in severe years. Fruit rot has not been observed in the Pacific Northwest on vines grown for wine.
This same fungus has also been found infrequently as a trunk pathogen causing cankers, interior wood discoloration, poor vigor, and dieback. Symptoms are similar to those of Botryosphaeria dieback or Eutypa dieback. Historically, the disease was called Dead Arm and is now referred to as Phomopsis dieback.
- Remove infected canes during normal pruning operations in the dormant season.
Chemical control Spray when shoots are 0.5 to 1 inch long and again when shoots are 5 to 6 inches long. Applications just before or just after cluster emergence helps manage rachis infections. Application of lime sulfur prior to or at bud break was useful in combination with in-season fungicides for control of this disease in Ohio. Rotate fungicides that have different modes of action. Group M3 and M4 fungicides are better than group 3, 7, or 11 fungicides.
- Abound at 10 to 15.5 fl oz/A. Do not apply within 14 days of harvest or with silicone-based surfactants. Sprayers should not be used on apples. Group 11 fungicide. 4-hr reentry.
- Aprovia at 8.6 to 10.5 fl oz/A plus an adjuvant. Do not use within 21 days of harvest. Group 7 fungicide. 12-hr reentry.
- Bonide Captan 50 WP at 1 to 1.5 Tbsp/gal water can be used in home gardens. H
- Captan 80 WDG at 1.25 to 2.5 lbs/A. May be applied up to the day of harvest. Do not use with oils, lime. or alkaline materials. Group M4 fungicide. 48-hr reentry.
- Cevya at 4 to 5 fl oz/A. Do not use within 14 days of harvest. Group 3 fungicide. 12-hr reentry.
- Cueva at 0.5 to 1 gal/100 gal water/A. May cause marginal leaf burn in some cultivars. Group M1 fungicide. 4-hr reentry. O
- Flint Extra at 3.5 to 3.8 fl oz/A. Do not use on 'Concord' grapes. Do not use within 14 days of harvest. Group 11 fungicide. 12-hr reentry.
- Hi-Yield Captan 50 W Fungicide may be used in home gardens at 1 to 1.5 Tbsp/gal water. H
- Mancozeb products such as Dithane, Manzate Pro-Stick, or Penncozeb at 1.2 to 2.5 lb/A. Do not apply within 66 days of harvest. Disease may be called "dead arm" on some labels. Group M3 fungicides. 24-hr reentry.
- Nu-Cop 50 DF at 2 to 6 lb/A. Group M1 fungicide. 48-hr reentry. O
- Oso SC at 6.5 to 13 fl oz/A. May be applied on the day of harvest. Group 19 fungicide. 4-hr reentry. O
- Sovran at 3.2 to 4.8 oz/A. Do not apply within 14 days of harvest. A marginal burn may develop on young leaves if an organosilicone-based adjuvant is used. May injure some sweet cherries, such as 'Van' if accidentally sprayed. Group 11 fungicide. 12-hr reentry.
- Ziram 76 DF at 3 to 4 lb/A. Group M3 fungicide. 48-hr reentry.
- Aprovia Top at 8.5 to 13.5 fl oz/A. Do not apply within 21 days of harvest. Group 3 + 7 fungicide. 12-hr reentry.
- Luna Sensation at 5 to 7.6 fl oz/A. Do not use on 'Concord' or within 14 days of harvest. Group 7 + 11 fungicide. 12-hr reentry.
- ManKocide at 2.5 lb/A. Do not apply within 66 days of harvest. May injure copper-sensitive cultivars such as Concord. Group M1 + M3 fungicide. 48-hr reentry.
- Miravis Prime at 9.2 to 13.4 fl oz/A. Do not use within 14 days of harvest. Group 7 + 12 fungicide. 12-hr reentry.
- Pristine at 8 to 12.5 oz/A. Do not use within 14 days of harvest. Do not use on labrusca-type grapes such as 'Concord' and 'Niagara' due to possible foliar injury. Group 7 + 11 fungicide. 12-hr or 5-day reentry based on activity.
- Quadris Top at 12 to 14 fl oz/A. Do not use within 14 days of harvest or on 'Concord' grapes. Group 3 + 11 fungicide. 12-hr reentry.
- Topguard EQ at 8 fl oz/A. Do not use with silicone surfactants or within 14 days of harvest. Sprayers should not be used on apples. Weak control. Group 3 + 11 fungicide. 12-hr or 5-day reentry based on activity.
Note Some registered products offer only suppression of this disease and thus are not recommended for use. These products include Luna Experience.
Although Gavel is registered, it contains a chemical for control of downy mildew, a disease not found on grape in the PNW and thus is not recommended for use.
- Serenade ASO (Bacillus subtilis strain QST 713) at 2 to 4 quarts/A. Active ingredient is a small protein. Unknown efficacy in the PNW but not expected to be good. 4-hr reentry. O
References Anco, D.J., Madden, L.V., and Ellis, M.A. 2013. Effects of temperature and wetness duration on the sporulation rate of Phomopsis viticola on infected grape canes. Plant Disease 97:579-589.
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.