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Mysterious White Patches on Lemon Tree Bark: Fungus, Canker, or Something Else?

Symptoms

Older lemon tree on central California coast. White patches on bark: mostly circular, discrete margins, slightly raised, scrape off with a bit of bark. Not noticeably fuzzy. Moderate climate with morning dew.

Possible Causes

Opportunistic fungus: Superficial growth on dead/damaged bark.
Citrus canker: Unlikely in California; would have distinct raised, corky lesions with yellow halos.

Next Steps

Examine lesions with a magnifying glass for fuzzy details (indicates fungal structures).
If possible, provide clear photos for remote diagnosis.
Avoid treatment until identified; unnecessary sprays can harm beneficial microbes.

Expert recommends further research and photo submission if possible.

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