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Canker

Plant disease

Description​

Canker is a general name for a localized area of dead bark and underlying tissue on a woody stem or branch, not a single disease with one scientific name. Various fungi and bacteria can cause it; injury and environmental stress can produce similar-looking damage. A canker may look sunken, cracked, discolored, or swollen around its edges. Some ooze sap or gum, while others develop small fungal fruiting bodies. As the affected tissue dies, the canker may enlarge and girdle a branch, interrupting the movement of water and nutrients. Leaves beyond it can wilt or die, and the branch may eventually die back. Cankers occur on many trees and shrubs, but their causes, appearance, and severity differ by host plant. A small canker on a removable twig is often manageable; one that encircles a trunk or main stem can seriously threaten the plant.

Symptoms​

  • Wilting
  • Leaves dropping
  • Stunted growth
  • Soft or rotting stems

How to Identify​

Look for a defined patch of dead, often sunken or cracked bark on a stem or branch, with dieback or wilting beyond it. The edge may be raised; gum, bacterial ooze, or tiny fungal fruiting bodies can sometimes provide clues. Check whether the damage is spreading beyond an obvious wound. Sunscald, frost cracks, mower injury, and insect damage can resemble canker but may lack an expanding area of dead tissue. A single photograph rarely identifies the cause: the host plant, season, and appearance of the lesion matter. For a valuable tree or a recurring problem, ask a local plant diagnostic service to examine a sample.

Prevention​

Choose plants suited to the site and, where available, varieties resistant to locally common canker diseases. Keep plants vigorous with appropriate watering and mulch, but avoid waterlogged soil and excessive nitrogen fertilizer. Protect trunks from mowers, string trimmers, and other injuries that can provide an entry point for pathogens. Space plants for airflow, and remove dead or infected branches promptly rather than leaving them as a source of inoculum. Prune in dry weather using sound cuts that leave the branch collar intact. The safest pruning season varies: for example, some stone fruits are best pruned during a dry summer period rather than in cool, wet weather. Clean pruning tools when moving between infected plants or branches.

Treatment​

First, confirm that the damage is a canker rather than an old injury. If it is confined to a small branch, prune that branch back into healthy wood, well below the visible lesion; allow a margin of about 15–30 cm (6–12 in) where practical. Disinfect tools between cuts, and dispose of infected prunings according to local guidance rather than leaving them beneath the plant. Support recovery with appropriate watering and by preventing further injury. Do not carve a canker out of a trunk or apply wound paint: neither reliably cures it. A canker that girdles the trunk or a main stem may make removal necessary, especially if the tree poses a safety risk. Fungicides and bactericides do not heal established cankers. For certain diagnosed diseases, a product labeled for that plant may help protect uninfected tissue, but timing and effectiveness vary; follow the label and seek local advice before spraying.

Plants Affected​

Alder, American Beech, American Chestnut, American Hornbeam, Aspen, Beech, Bigtooth Aspen, Black Cottonwood, Black Locust, Black Walnut, Blue Beech, Camellia, Cherry, Cherry Blossom, Chestnut, Chinese Chestnut, Cork Cypress, Cork Oak, Cork Redwood, Cork Sequoia, Cork Spruce, Cornus, Cypress, Eastern Cottonwood, European Beech, European Chestnut, European Hornbeam, Fir, Honey Locust, Horse Chestnut, Kerria, Larch, Locust, London Plane, Middlemist Red, Mountain Ash, Orange, Parsnip, Poplar, Quaking Aspen, Red Twig Dogwood, Redbud, Redwood, River Red Gum, Salix, Sequoia, Spruce, Trembling Aspen, Walnut, Water Oak, Willow, Yellow Birch

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