# Common tree diseases: what to record before a diagnosis

Recognize signs worth reporting without treating a photo or app as a diagnosis.

Updated 2026-11-10. Also on the [web page](https://arborists.fyi/guides/common-tree-diseases).

A symptom is a clue, not a diagnosis. Take photos from safe ground. Record the tree type if known, the affected parts and when you first noticed the change. Keep older photos if they show how the crown changed.

## Oak wilt

University of Minnesota Extension describes oak wilt as a fungal disease. It can spread through connected roots and by insects. The page describes browning leaf edges, wilting and leaf loss. It warns that other diseases can cause similar symptoms and recommends an accurate diagnosis before control action. [University of Minnesota Extension, Oak wilt in Minnesota, fetched 2026-11-10](https://extension.umn.edu/plant-diseases/oak-wilt-minnesota).

If you suspect oak wilt, tell the arborist about nearby oaks, recent wounds and recent tree work. Ask about the local disease status and the right diagnostic service. Do not use the Minnesota page as proof that oak wilt is present in another region. Do not move suspect wood before you obtain local advice. The source warns against moving firewood from affected areas.

## Apple scab

Minnesota Extension describes apple scab as a fungal disease of apples and crabapples. It identifies olive-green to brown leaf spots and possible early leaf drop. Its guidance includes resistant varieties, leaf cleanup and a canopy that allows air movement. [University of Minnesota Extension, Apple scab, fetched 2026-11-10](https://extension.umn.edu/plant-diseases/apple-scab).

Record whether fruit is affected and whether the tree lost leaves in earlier seasons. Tell the arborist whether the fruit is for eating. The source distinguishes treatment uses and stresses timing. Do not buy a fungicide from a photo match alone. Ask for a diagnosis and a reasoned care plan.

## Build a useful observation record

Use a separate note for each tree. Include:

- The address and a map label for the tree.
- Photos of the whole tree, affected leaves and visible trunk changes.
- Which side or part of the crown changed first.
- Watering, drainage changes and recent construction you know about.
- Previous reports and treatments, with their dates.

Leave unknown items blank. Avoid cutting a sample before the diagnostic service tells you what it needs. Ask where to send the sample and how to label it.

## Ask for a care decision

Ask the assessor to distinguish observation, likely cause and confirmed diagnosis. Ask which action is urgent and which can wait for testing. Request a plan that states the purpose of any treatment, its follow-up and what change would require another visit.

Do not infer disease from leaf colour alone. Do not infer that a sick-looking tree must be removed. Ask the assessor to explain the retention options and the limits of the inspection. If there is an immediate safety concern, keep people away and seek urgent professional help.

## Sources

Both University of Minnesota Extension pages above were fetched 2026-11-10. Their geographic context is Minnesota. Use local diagnostic and pest advice in other regions.

## Questions

### Can a tree identification app diagnose disease?

Use it to organize observations. The extension source recommends an accurate diagnosis before oak wilt control. Ask a qualified assessor or plant diagnostic service.