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Red Rot

Disease

Red rot is a fungal disease that primarily attacks the internal tissues of woody stems. It matters because it compromises the structural integrity of the plant, often leading to internal decay that is hidden until significant damage has occurred.

Symptoms by part

Stems

The internal wood turns a reddish or brownish color and becomes soft, brittle, or spongy to the touch.

Causes

  • Wounds on the stem caused by pruning or mechanical damage
  • Excessive moisture trapped against the bark
  • Poor air circulation around the main trunk or branches
  • Stressed plants with weakened natural defenses

Could be confused with

  • Heart rot · Heart rot typically affects the very center of the trunk and is often associated with older, mature trees, whereas red rot can appear in younger stems.
  • Sunscald · Sunscald causes bark to crack and peel on the outer surface, while red rot focuses on the internal decay of the wood beneath the bark.

Treatment

  1. Prune away branches showing signs of internal discoloration using sterilized tools.
  2. Cut back into healthy, firm wood to ensure all infected tissue is removed.
  3. Clean your pruning shears with a solution of rubbing alcohol between every single cut to prevent moving the fungus to healthy parts of the plant.

Without chemicals

  • Improve air circulation by thinning out crowded branches.
  • Ensure the plant is not sitting in waterlogged soil.
  • Avoid making large pruning cuts that leave big wounds open to infection.
  • Use a rain cover or shelter if the plant is in a container to keep the stems dry during wet spells.

Preventing it

  • Keep pruning tools sharp and clean to make smooth cuts that heal quickly.
  • Avoid wounding the bark with lawn equipment or garden tools.
  • Provide adequate spacing between plants to encourage airflow.
  • Water at the base of the plant rather than overhead to keep the stems dry.

Season

The warm growing season when humidity is high and fungal spores are most active.

Spread risk

Moderate

Severity

High

When to act

Act as soon as you notice discolored or soft wood during pruning. If the rot has reached the main trunk or the plant shows signs of structural instability, consult a professional tree surgeon to assess if the plant can be saved or must be removed for safety.

Think it's Red Rot?

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 plant with red rot?
If the infection is limited to a few small branches, you can often save the plant by pruning them out. If the rot has moved into the main trunk, the plant is likely too far gone.
Is red rot contagious?
Yes, it can spread to other plants through spores carried by wind or water, or by using contaminated pruning tools.

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