See:
Peach (Prunus persica) - Cytospora Canker
Grape (Vitis spp.) - Eutypa Dieback
Cause Although bacterial canker (Pseudomonas) dominates the canker diagnoses in the PNW, several cankers submitted to the OSU Plant Clinic were found to be caused by different fungal pathogens including Cytospora, Diaporthe (formerly Phomopsis), Eutypa, and Calospheria. Some fungal cankers may have been misidentified since bacterial canker can follow infection by these pathogens.
Cytospora canker has been the most prevalent since these are vigorous wound invaders (including wounds from sunscald and winter injury) that ramify throughout the bark and cambium and to a lesser extent the tree's structural wood. The specific pathogen(s) in the PNW has not been formally identified but the fungi Cytospora cincta (sexual: Leucostoma cinctum), and the closely related C. leucostoma (sexual: Leucostoma persoonii) have been suggested. These fungi have a wide host range and can infect virtually all stone fruit and pome fruit trees. Overwintering is in infected stems and stem debris on the ground. Conidia are produced in cherry and peach orchards in eastern Washington throughout the year and the inoculum concentration is highest during the spring and summer. Over-the-canopy and under-tree sprinkler irrigation can promote sporulation and disperse conidia.
Eutypa dieback, caused by Eutypa lata var. lata, can attack many hosts including all Prunus spp., apples, pears, grapes and walnuts and plants gown as ornamentals, or in riparian areas, such as big leaf maple, and willow. 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. In general, pruning wounds made early in the dormant period are much more susceptible than wounds made late in the dormant period.
Calosphaeria canker, caused by Calosphaeria pulchella, has not been diagnosed often in the past on cherry but has been found on both sides of the Cascades in Oregon. Cases may be increasing throughout the PNW as more samples are collected. Ascospores are also the primary inoculum for this disease originating primarily from within orchards. Wet weather and irrigation encourage dissemination of ascospores. Ascospores initiate infection through pruning wounds and sunburn lesions. Infections of pruning wounds are more likely to occur during periods of warm temperatures in the summer if inoculum is present.
Symptoms All of these diseases are noticed either in the spring when buds fail to sprout and foliage appears stunted and/or in summer when dead limbs become apparent following heat or water stress. Symptoms include branch and main scaffold dieback as well as cankers and vascular necrosis. Leaves above stem infections droop and discolor through shades of green to various shades of brown; they remain attached, sometimes through the winter. These flag shoots are caused by stem invasions that that girdle or nearly girdle the stem immediately below the flag.
Cankers are small at first but slowly enlarge elliptically; sometimes they streak rapidly up and down the stem without immediate girdling. Cankers are sunken due to dead tissue in the middle and living tissue at distinct margins that continue to grow. Cankers may or may not have gummosis. For Cytospora canker, a callus forms at the canker margins and it stops growing but fungal activity resumes again next spring. If not removed, continued expansion of these cankers each year gives it an elliptical look with concentric rings, which is why it has also been called perennial canker. Eutypa dieback has a V shaped discoloration in cross section of branch but other canker pathogens such as Botraspheria can cause similar symptoms.
Cytospora canker surfaces develop scattered raised pinhead-size pimples (pycnidia) that push through the bark, but these may not be readily visible. Amber to orange, hair-like spore tendrils extrude from the pycnidia in humid weather. These break off easily and can be blown about, tracked around by insects, and splashed by rain. In very wet weather, an amber spore droplet instead of the spore hair may form on the pycnidia. Calosphaeria canker produces perithecia in groups with long necks that emerge together through the bark at lenticels. Eutypa dieback fruiting bodies may not be seen at all or only when the bark is scraped back. Once they are produced black perithecia can be seen embedded in black stromata.
Cultural control
- Remove dead branches, cutting well below (at least 1 ft) any visible discoloration in the bark. Infected material should be removed from the orchard and destroyed if possible.
- Do not establish new orchards close to or downwind from badly diseased orchards.
- Treetop or other hedgerow pruning and overhead irrigation are not advised where the disease is a problem.
- Take special care to avoid wounding trees during the growing season. Tractors and sprayers commonly inflict such wounds, as do shakers, ladders, and pickers' feet.
- Control all insect and disease problems, such as brown rot of stone fruits, even in the first few nonbearing years.
- Train trees properly.
- Avoid rodent injury.
- Avoid excessive nitrogen fertilization, nitrogen applications late in the growing season, or late-season cultivation or irrigation.
- Paint the southwest side of tree trunks with white latex paint to avoid winter injury.
- Prune as late as possible in the dormant season. Prune in dry weather.
- Summer pruning can be helpful as long as wounds can be kept dry for 2 to 3 weeks.
- Surgically remove cankers from trunks and scaffold limbs in summer.
- 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 Use of latex paint, Captan and/or Topsin was shown to be effective wound protectants prior to Cytospora infection in Colorado. Latex paint, however, did not result in long term effective control while lime sulfur gave variable results. Use of these materials after pruning or winter injury may be helpful. Use of copper-based fungicides was ineffective.
- 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.
References Grove, G. G., and Biggs, A. R. 2006. Production and dispersal of conidia of Leucostroma cinctum in peach and cherry orchards under irrigation in Eastern Washington. Plant Disease 90:587-591.
Li, S., Travadon, R. and Trouillas, F. P. 2023. Seasonal Susceptibility of Sweet Cherry Pruning Wounds to Calosphaeria pulchella, Cytospora sorbicola, and Eutypa lata. Plant Disease, 107:3517-3522.