tree health

Most Unwanted: pests and diseases


These are six pests and diseases that could have a very serious impact on our trees.

You are unlikely to find most of them during your OPAL survey, as they are not widespread or not yet present in the UK. But if you do find them, it is important that you take the right action immediately.

If you think you have spotted one of the Most Unwanted, it is essential that you alert Forestry Commission officials through:

Oak pests and diseases


Oak mildew

Oak mildewOak mildew is caused by the fungus Erysiphe alphitoides. It was first found in England in 1908 and is now common throughout Europe.

It infects younger leaves and soft shoots, especially the second growth of leaves in summer. Its severity varies according to the weather conditions in a particular year, and it is worst during warm, wet summers when humidity is high.


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