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Canker

Disease

Canker is a fungal disease that creates localized dead areas on the bark of woody stems. It matters because these lesions can girdle branches or trunks, cutting off the flow of water and nutrients to the rest of the plant.

Symptoms by part

Stems

Sunken or discolored patches on the bark, often accompanied by oozing resin or sap. You may also see foliage on a specific branch turning yellow or brown while the rest of the plant remains green.

Causes

  • Wounds on the bark from pruning or storm damage
  • High humidity or frequent rainfall that keeps bark wet
  • Drought stress that weakens the plant defense system
  • Splashing water that carries fungal spores onto open wounds

Could be confused with

  • Aphid damage · Aphids leave sticky honeydew and often cause distorted growth, whereas canker causes distinct sunken lesions and dead patches on the wood.
  • Winter injury · Winter damage usually affects the tips of branches uniformly, while canker creates localized, specific dead zones on larger stems.

Treatment

  1. Prune out infected branches at least 6 to 10 inches below the visible lesion to ensure all diseased tissue is removed.
  2. Sterilize your pruning shears with a solution of 70 percent isopropyl alcohol between every single cut to prevent spreading the fungus.
  3. Dispose of all pruned material by burning or burying it away from your garden, never compost it.

Without chemicals

  • Prune during dry weather to allow wounds to seal quickly.
  • Improve air circulation around the plant by thinning out dense foliage.
  • Provide deep, consistent watering during dry spells to reduce plant stress.
  • Use a rain cover or protective structure if the plant is small enough to keep the foliage and stems dry during wet spells.

Chemical options

  • Tebuconazole, apply as a systemic spray to the foliage and stems to protect healthy tissue, follow the label.
  • Triticonazole, apply as a protective spray to the bark and foliage, follow the label.

Preventing it

  • Avoid wounding the bark with lawn mowers or string trimmers.
  • Water at the base of the plant rather than overhead to keep stems dry.
  • Select resistant varieties when planting new cypress trees.
  • Maintain plant vigor with proper spacing to ensure good airflow.

Season

The warm growing season, especially during periods of high humidity or heavy rain.

Spread risk

Moderate

Severity

High

When to act

Act as soon as you notice a branch turning brown or see oozing on the bark. If the canker has reached the main trunk, consult a professional tree surgeon to assess if the tree can be saved or if it must be removed.

Think it's Canker?

This guide covers the general picture. Pocket Botanist looks at your actual plant from a photo and tells you what's really going on, how serious it is, and what to try first. Identification and a health check are free.

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Questions people ask

Can I save a branch that has a canker?
Usually no. Once the fungus has established a lesion, the tissue is dead and will not recover. Pruning it out is the best way to stop it from spreading to the rest of the tree.
Will my tree recover if I just leave the canker alone?
It is unlikely. Cankers tend to expand over time, eventually girdling the branch or trunk and killing the parts of the plant above the infection site.
Does pruning spread the disease?
Yes, if you do not clean your tools between cuts. The fungus can easily travel on your shears from an infected branch to a healthy one.

Plants it affects

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This guide was generated with AI and is general information, not horticultural advice. Read about how we build these guides.