White fungus on a Japanese maple

Written by mark bingaman
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White fungus on a Japanese maple
A powdery mildew infection may jump aboard a Japanese maple. (Image by Avlxyz; Flickr.)

Nearly all ornamental plants suffer infection from a fungal disease known as powdery mildew. Japanese maple trees are likely to survive an attack, although the disorder can be unsightly with a white, powdery growth coating the plant's otherwise attractive-looking leaves.

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A white fungus known as powdery mildew is one of several leaf diseases prone to attacking the brightly coloured Japanese maple tree, Acer palmatum. Japanese maples may also be troubled by anthracnose, leaf spot, leaf scorch, root rot, aphids, scales and borers.

Powdery mildew

Powdery mildew appears as a white or grey fungal substance throughout the leaves, stems, flowers and fruit of a plant. Leaves may curl or twist even before the white fungus is apparent. Severe powdery mildew infection will result in yellowed leaves, dried and brown leaves, and disfigured shoots and flowers.


The disease rarely results in the death of the Japanese maple, but it may increase the likelihood of leaves falling prematurely and the tree moving into autumn dormancy earlier than normal. Trees typically suffer infection when temperatures range between 15C and 27C; powdery mildew normally does not appear during the extreme heat of summer or cold of winter.

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