Predominately found in stone fruits such as peach, nectarine, prune, plum, and sweet cherry, the Cytospora canker is also known as peach canker, perennial canker, and Valsa canker. Color photographs enhance the discussion of disease cycle, symptoms, and management. 2 pages

Grove, Gary

Johnson, Dennis

Regner, Kurt

Washington State University  institutional repository

EB1448  CYTOSPORA CANKER OF STONEFRUITS   Cytospora canker is a destructive disease of treefruits in Washington. Although most common onstone fruits, the disease can be encountered onapple. Also known as peach canker, perennialcanker, and Valsa canker in some areas, thedisease occurs wherever stone fruits are grown.The disease is general in occurrence in peach,nectarine, prune, plum, and sweet cherry orchardsin Washington, and limits President plumproduction in Idaho. Cytospora canker isassociated with winter-injured or mechanicallywounded twigs, trunks, and scaffold branches.Cytospora canker is caused by either of two fungispecies, Cytospora leucostoma or Cytosporacincta. These two fungi are very similarmorphologically and can be definitivelyseparated only by microscopic examination of thesexual fruiting structures. These structures, calledperithecia, are not frequently found.    Disease Cycle  The Cytospora fungi are vigorous woundinvaders that grow throughout the bark andcambium and to a lesser extent into the structuralwood of the tree. Common infection sites arebark that has been killed or injured by low wintertemperatures or sunburn, pruning cuts, or insectdamage. Winter injury is frequently an importantpredisposing factor to infection. Once establishedin dead or weakened tissue, the Cytospora fungiwill invade adjacent healthy tissue, causingdieback (Fig. 1) and stem cankers.As cankers enlarge, the fungus produces pinhead-sized, black, pimplelike, spore-producingstructures, called pycnidia. These structures produce millions of spores, called conidia.During wet weather, spores ooze out of thespore-producing structures in reddish to orangecolored gelatinous masses (Fig. 2). Spores arecarried to other infection sites (that is, wounds onthe same or nearby trees) by splashing andwindblown rain, insects, or people. These sporesare not adapted to wind dispersal. Sporesgerminate at wound sites, resulting in infectionand eventual cankering. Spore-producingstructures ultimately form in the new cankers,producing more spores for subsequent infections.The spore-producing structures generally form 4to 6 weeks after a cankered branch dies. Thefungus overwinters in diseased tissue of livinghosts and in stem debris on the ground.If cankers are allowed to remain for severalyears, a second spore-producing structure, theperithecium, develops in the diseased tissue andproduces ascospores. Ascospores are wind-disseminated; infection can result if moisture ispresent when ascospores are blown againstwounded host tissue.Infection can occur anytime during the year,except during very hot and dry, or cold weather.In Idaho, most infections occur during spring andearly summer when temperatures are mild andmoisture from rainfall is high.  Fig. 1. Plum tree infected withCytospora sp. showing dieback anda "flag."    Fig. 2. Spore-forming structures oncherry; some with gelatinousmatrix of spores.     Disease Symptoms  Usually, the first symptoms of infection are deadtwigs and dieback. Leaves above stem infectionsdroop and discolor through shades of green tovarious shades of brown, and often remainattached, sometimes through the winter. These "flags" (Fig. 1) are caused by stem invasions andgirdling or near-girdling cankers immediatelybelow the flag.Cankers are dark and depressed areas of deadbark and wood on main leaders and branches.Canker margins are sharp and distinct (Fig. 3) onthe bark and discolored wood. Cankers arefrequently perennial and may assume a zoneateappearance. Young cankers usually exude gum atthe margin and may have a sour, sap odor. Thesurface of the cankers may develop raisedpinhead-sized pycnidia in the bark. The spore-forming structures are rarely produced on cherrystems. After rainy weather, tendrils of driedreddish-orange ooze are sometimes visiblecoming from pycnidia (Fig. 4).Small at first, cankers slowly enlarge elliptically;sometimes they streak rapidly up and down thestem without girdling it immediately.  Fig. 3. Canker margin on apeach tree.     Fig. 4. Pyonidia and tendrils ofdried spores on infected cherrytree.     DiseaseManagement There is currently no cure for infected trees.Prevention and sanitation practices are the bestmanagement approaches. Use the following threesteps concurrently.1. Minimize injuries. Winter injuries are themost common infection sites. Painting tree trunkswhite before winter has reduced Cytosporainfections. Take other measures to reduce winterinjury and maintain good tree vigor. 2. Remove and destroy infected wood. Pruneout infected branches, flags, cankers, andmaintain good orchard sanitation. Cytospora hasbeen isolated from apparently healthy tissue oncankered branches. Make pruning cuts at leastone foot below the infected area.3. Prune correctly. Make cuts that leave a raisedcollar of tissue at the branch junction rather thanflush cuts or cuts that leave a stub. Pruning in thespring when wounds heal most rapidly haseffectively reduced disease incidence in someareas.Do not establish new orchards close to badlydiseased orchards. Treetop or other hedgerowpruning and overhead irrigation favor the disease.Maintain trees in good vigor, but with maximumhardiness. Trees under water stress or grown inpotassium-deficient soil are susceptible toinfection. Weakened trees easily become victimsof the Cytospora fungi.    By Gary G. Grove, Extension Plant Pathologist, Washington State University (WSU) Tree FruitResearch Center, Wenatchee; Kurt M. Regner, Research Assistant in Plant Pathology, WSU, Pullman;and Dennis A. Johnson, Extension Plant Pathologist, WSU Irrigated Agriculture Research and ExtensionCenter, Prosser.Issued by Washington State University Cooperative Extension and the U.S. Department of Agriculture infurtherance of the Acts of May 8 and June 30, 1914. Cooperative Extension programs and policies areconsistent with federal and state laws and regulations on nondiscrimination regarding race, color, gender,national origin, religion, age, disability, and sexual orientation. Evidence of noncompliance may bereported through your local Cooperative Extension office. Trade names have been used to simplifyinformation. No endorsement is intended. Published August 1987. A. Subject Code 356. EB1448

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Cytospora Canker of Stone Fruits

https://rex.libraries.wsu.edu/esploro/outputs/report/Cytospora-Canker-of-Stone-Fruits/99900502314901842

Cytospora Canker of Stone Fruits

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