Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Peach -- Cytospora Canker
 
Cause: Leucostoma cincta (asexual: Cytospora cincta), fungus, and the closely related Leucostoma persoonii (asexual: C. leucostoma). These are vigorous wound invaders (including wounds from sun scald and winter injury) that ramify throughout the bark and cambium and to a lesser extent the tree's structural wood.

Overwintering is in infected stems and stem debris on the ground. These fungi have a wide host range and can infect virtually all stone fruit and pome fruit trees. They can be devastating in cherry, peach, and apricot orchards. Conidia are produced in cherry and paech 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. Cankers have been reported on apple in all Pacific Northwest regions, especially after severe winters. Various ornamental shrubs and trees are susceptible as well. All these hosts can provide overwintering sites. Cytospora fungi do not destroy the tree's structural strength, but other fungi (principally the genera Stereum and Polyporus) commonly invade the Cytospora infection sites and cause rapid wood rotting, which adds to the severity of the disease's effects.

Symptoms: To the casual observer, the first evidence of infection usually is dead twigs. Leaves above stem infections droop and discolor through shades of green to various shades of brown; they remain attached, sometimes through the winter. These "flags" are caused by stem invasions that have raised cankers that girdle or nearly girdle the stem immediately below the flag. Canker surfaces develop raised pinhead-size pimples (pycnidia) in the bark of most smooth-bark cultivars, but these may not be readily visible in cankers on peach and cherry stems. 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.

Cankers are small at first but slowly enlarge elliptically; sometimes they streak rapidly up and down the stem without immediate girdling. In late season, a callus forms at canker margins, and fungal activity resumes in spring. If branches and trees do not die outright, they look very ragged; this stage is often known as perennial canker. All cultivars are susceptible, but reaction to invasion varies widely. Weakened trees are always easy victims. In Idaho, this disease is the limiting factor in 'President' plum production.

Note the cankered area on the lower portion of this trunk.

This infected peach twig has numerous dark pycnidia of the fungus.

Infected twigs turn brown and eventually gray. Small black fruiting bodies form in the dead tissues.

 
Cultural control:
  1. Remove dead branches, cutting well below (at least 1 ft) any visible discoloration in the bark. Paint wounds immediately with a disinfecting solution.
  2. Do not establish new orchards close to or downwind from badly diseased orchards.
  3. Treetop or other hedgerow pruning and overhead irrigation are not advised where the disease is a problem.
  4. 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.
  5. Control all insect and disease problems, such as brown rot of stone fruits, even in the first few nonbearing years.
  6. Train trees properly.
  7. Avoid rodent injury.
  8. Avoid excessive nitrogen fertilization, nitrogen applications late in the growing season, or late-season cultivation or irrigation.
  9. Paint the southwest side of tree trunks with white latex paint to avoid winter injury.
  10. Prune as late as possible in the dormant season. Prune in dry weather.
  11. Summer pruning should be avoided if the disease is a problem. If pruning can not be avoided, let wounds heal for 14 to 21 days before irrigation is started again.
  12. Surgically remove cankers from trunks and scaffold limbs in summer.
References:
Biggs, A.R. 1989. Integrated approach to controlling Leucostoma canker of peach in Ontario. Plant Disease 73:869-874.
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.
Content edited by: Jay W. Pscheidt on January 1, 2009
 
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