Removing Lichen from Apple Trees: Safe Methods and Timing

An apple tree owner asks whether caustic soda (sodium hydroxide) can safely remove lichens and fungus, and whether winter or summer application is better.

Understanding Lichen on Fruit Trees

Lichens are symbiotic organisms (fungus + algae) that grow on bark surfaces. They don't parasitize the tree but can indicate poor vigor, excessive shade, or high humidity. Heavy growth may harbor pests and diseases.

Risks of Caustic Soda

Caustic soda is highly corrosive (pH ~14) and can severely damage living bark tissue, cambium, and buds. It's not labeled for horticultural use and poses significant safety risks to the applicator. Do not use household caustic soda on trees.

Safe, Effective Alternatives

1. Mechanical Removal (Winter/Dormant Season)

• Use a soft brush or plastic scraper on dormant trees
• Work gently to avoid bark injury
• Best done in late winter before bud break

2. Lime Sulfur or Copper Sprays (Dormant Season)

• Apply registered dormant sprays per label directions
• These suppress lichen, moss, algae, and overwintering pests/diseases
• Timing: Late winter, before green tip stage

3. Commercial Lichen/Moss Removers

• Products containing potassium salts of fatty acids or similar
• Follow label rates and safety precautions
• Test on small area first

4. Cultural Management

• Improve air circulation with proper pruning
• Reduce excessive shade
• Maintain tree vigor with appropriate fertilization
• Ensure good drainage

Best Timing

Late winter (dormant season) is ideal—before bud break, when temperatures are above freezing but tree is still dormant. This avoids foliage damage and targets overwintering organisms.

Always read and follow product labels. When in doubt, consult your local cooperative extension for region-specific recommendations.