Cytospora Canker

Cytospora spp. (Valsa spp., Leucostoma spp.)

136 host plants

Last updated

Data Maturity Structured

This profile synthesizes data from multiple published sources. Expert field review is in progress.

Cytospora canker manifests as dead twigs and branches in spring, with foliage above the infection turning brown while remaining attached to the stem (creating "flags"). The canker itself appears as a sunken, elongated lesion in the bark, often with visible pinhead-sized fruiting bodies; in humid weather, you may spot amber or orange spore tendrils extruding from the bark. The fungus is vigorous in exploiting wounds from winter injury, sunscald, frost cracks, or pruning, and once it establishes in the cambium, it slowly girdles the stem. This disease affects pome fruits, stone fruits, and ornamental trees including oak and aspen.

Cytospora canker becomes a serious problem when trees are stressed and wounded, particularly in spring and early summer as the fungus resumes activity. Minimize damage by avoiding pruning wounds during the growing season, training trees properly to reduce branch breakage, and protecting against rodent damage and frost crack. Do not over-apply nitrogen or irrigate late in the season, as vigorous growth followed by cold snaps creates ideal conditions for canker formation. If you spot infected branches, prune them off at least a foot below any visible discoloration, sterilizing tools between cuts, and avoid establishing new orchards near badly diseased ones where inoculum loads remain high.

Quick Reference

Causal Agent
Cytospora spp. (Valsa spp., Leucostoma spp.)
Host Plants
136
Spread
Conidia released as amber spore tendrils or droplets from pycnidia in wet con...
Favorable Conditions
Cytospora cankers reactivate with spring sap flow (March–May in Pacific North...

Management

Vulnerability Window

Peak infection risk during spring through early summer (April–July) when sap flow is rapid and wounds from pruning or weather damage are fresh. Spring wound entry establishes infections that expand through late spring into summer (May–Aug). Cankers reactivate each spring during dormancy break, with damage visible as branch flags in early growing season. Winter injury and frost cracks create late-season (November–March) wounds that become infection sites when sap flow resumes in spring. Trees are especially vulnerable when stressed from drought, nutrient imbalance, or poor vigor (BBCH 10–70, bud break through active growth).

What Triggers Infection

Cytospora cankers reactivate with spring sap flow (March–May in Pacific Northwest); fungal activity is greatest during warm, moist periods (75–85°F with high humidity). Spore release is triggered by prolonged moisture (rain, dew, irrigation). Wounds are essential for infection entry; sources include pruning, frost cracks, sunscald damage, winter injury, and branch breakage. Stressed, weakened, or poorly vigorous trees are most susceptible. Overhead irrigation, late-season nitrogen, and dense shade all increase risk. The fungus exploits any break in the bark.

Cultural Controls

  • Remove dead branches, cutting well below (at least 1 ft) any visible discoloration in the bark.
  • 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.
  • Train trees properly.

Host Plants (136)

Asimina triloba Common Pawpaw Custard Apple Betula lenta Sweet Birch, Cherry Birch, Black Birch Eucalyptus cinerea Silver Dollar Eucalyptus, Silver Dollar Gum Argyle Apple Malus 'Indian Magic' Indian Magic Crabapple Malus atrosanguinea Carmine Crabapple Malus brandywine Brandywine Crabapple Malus floribunda Japanese Flowering Crabapple Malus fusca Pacific Crabapple Malus hupehensis Tea Crabapple Malus prairifire Prairifire Crabapple Malus pumila Apple Malus robusta Cherry, Crabapple Malus sargentii Sargent Crabapple, Pigmy Crabapple Malus snowdrift Snowdrift Crabapple Malus transitoria Transitoria Crabapple Picea abies Norway Spruce Picea abies var. pendula Weeping Norway Spruce, Pendulous Norway Spruce Picea asperata Dragon Spruce Picea breweriana Brewer Spruce, Brewer's Weeping Spruce Picea engelmannii Engelmann Spruce Picea gemmata Szechwan Spruce Picea glauca White Spruce, Canadian Spruce, Skunk Spruce Picea koyamae Koyama's Spruce, Yatsugatake-tohi [Japanese] Picea mariana Black Spruce, Bog Spruce, Swamp Spruce Picea omorika Serbian Spruce Picea orientalis Caucasian Spruce, Oriental Spruce Picea pungens Colorado Spruce Picea pungens var. glauca Colorado Blue Spruce Picea rubens Red Spruce Picea sitchensis Sitka Spruce Picea wilsonii Wilson's Spruce Populus alba White Poplar European White Poplar, Silver Poplar Populus angustifolia Narrowleaf Cottonwood, Mountain Cottonwood Populus balsamifera Balsam Poplar Populus canescens Gray Poplar Populus deltoides Eastern Cottonwood Populus fremontii Fremont Cottonwood, Western Cottonwood Populus grandidentata Bigtooth Aspen Populus nigra Black Poplar Populus tremula European Aspen European Trembling Aspen European Quaking Aspen Populus tremuloides Quaking Aspen Populus trichocarpa Black Cottonwood Prunus americana Wild Plum American (Red) Plum August Plum, Goose Plum Prunus armeniaca Apricot Prunus avium Sweet Cherry Prunus besseyi Sand Cherry, Western Sand Cherry Prunus blireiana Blireiana Plum Prunus caroliniana Carolina Cherrylaurel American Cherrylaurel Prunus cascade Prunus cascade Prunus cerasifera Cherry, Plum Prunus cistena Purpleleaf Sandcherry Redleaf Sandcherry Cistena Sandcherry Cistena Plum Prunus dream Prunus dream Prunus emarginata Bitter Cherry, Wild Cherry, Quinine Cherry Prunus first Prunus first Prunus fruticosa Steppe Cherry, European Dwarf Ground Cherry, Mongolian Cherry Prunus glandulosa Dwarf Flowering Almond Prunus ilicifolia Hollyleaf Cherry, Holly-leaved Cherry Prunus laurocerasus Cherry, Laurel Prunus lusitanica Portugal Laurel Prunus maackii Amur Chokecherry Amur Cherry, Manchurian Cherry Prunus mume Japanese Apricotc Japanese Flowering Apricot Japanese Flowering Plum Prunus newport Newport Flowering Plum Prunus okame Okame Flowering Cherry Prunus padus European Birdcherry Common Birdcherry Prunus prostrata Rock Cherry, Mountain Cherry Prunus sargentii Sargent Cherry, Sargent's Cherry Prunus serotina Black Cherry, Rum Cherry Prunus serrula Birchbark Cherry, Paperbark Cherry, Tibetan Cherry Prunus serrulata Japanese Flowering Cherry Prunus snow Prunus snow Prunus subcordata Klamath Plum, Sierra Plum, Pacific Plum Prunus subhirtella Higan Cherry Prunus subhirtella var. autumnalis Autumn Flowering Higan Cherry Prunus tai Prunus tai Prunus virginiana Prunus virginiana Prunus virginiana var. demissa Western Chokecherry Prunus virginiana var. virginiana Common Chokecherry, Eastern Chokecherry Prunus yedoensis Yoshino Cherry, Somei-yoshino Cherry, Tokyo Cherry Quercus acutissima Sawtooth Oak Quercus agrifolia Coast Live Oak Quercus alba (Eastern) White Oak Quercus arizonica Arizona Oak, Arizona White Oak Quercus berberidifolia California Scrub Oak, Scrub Oak, Inland Scrub Oak Quercus bicolor Swamp White Oak Quercus bimundorum Two Worlds Oak, Bimundors Oak Quercus castaneifolia Chestnut-leaved Oak, Chestnutleaf Oak, Persian Oak Quercus cerris Turkey Oak Quercus chrysolepis Canyon Live Oak Quercus coccinea Scarlet Oak Quercus douglasii Blue Oak, California Blue Oak Quercus durata Leather Oak Quercus emoryi Emory Oak, Black Oak, Blackjack Oak Quercus engelmannii Engelmann Oak, Mesa Oak Quercus frainetto Hungarian Oak, Italian Oak Quercus gambelii Gambel Oak, Rocky Mountain White Oak Quercus garryana Oregon White Oak Quercus garryana var. breweri Brewer's Oak Quercus glandulifera Konara Oak Quercus glauca Japanese Blue Oak, Ring-cupped Oak Quercus hypoleucoides Silverleaf Oak, Whiteleaf Oak Quercus ilex Holly, Oak, Holm Oak Quercus ilicifolia Bear Oak Quercus imbricaria Shingle Oak Quercus kelloggii California Black Oak Quercus leana Lea's Oak Quercus lobata Valley Oak, Roble Oak, California White Oak Quercus macrocarpa Bur Oak, Mossycup Oak Quercus marilandica Blackjack Oak, Jack Oak Quercus mongolica Mongolian Oak Quercus montana Mountain Chestnut, Oak, Chestnut, Oak, Rock Chestnust Oak Quercus muehlenbergii Chinkapin Oak, Chinquapin Oak, Yellow Chestnut, Oak Quercus myrsinifolia Chinese Evergreen Oak, Bamboo-leaf Oak Quercus nigra Water Oak, Possum Oak Quercus palustris Pin Oak, Swamp Spanish Oak Quercus petraea Sessile Oak, Durmast Oak, Irish Oak Quercus phellos Willow, Oak Quercus prinoides Dwarf Chinquapin Oak, Dwarf Chestnut, Oak, Scrub Chestnut, Oak Quercus robur English Oak Quercus rubra Northern Red Oak Quercus sadleriana Sadler Oak, Deer Oak Quercus stellata Post Oak Quercus suber Cork Oak Quercus turbinella Scrub Live Oak Quercus undulata Wavyleaved Oak Quercus vaccinifolia Huckleberry, Oak Quercus velutina Black Oak Quercus virginiana Southern Live Oak, Live Oak Quercus wislizeni Interior Live Oak, Chapparal Oak Sorbus alnifolia Korean Mountain Ash, Alder, Mountain Ash Sorbus aria Whitebeam Mountain Ash Sorbus aucuparia European Mountain Ash Sorbus koehneana Chinese Mountain Ash, White-fruited Chinese Mountain Ash Sorbus poteriifolia Mountain Ash Sorbus scopulina Greene Mountain Ash, Western Mountain Ash Sorbus sitchensis Sitka Mountain Ash, Pacific Mountain Ash, Western Mountain Ash Sorbus yunan Sorbus yunan (no English common name)