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Josef Rauscher Studio

Bonsai care · Acer campestre

Powdery mildew on field maple

A white, mealy coating forms on young leaves and shoots shortly after budding.

Josef Rauscher

Maple leaf with a whitish coating and brown discolouration along its edges.
Maple leaf with a whitish coating and brown discolouration along its edges.
Pale coating and brown discolouration on a maple leaf.
Pale coating and brown discolouration on a maple leaf.
Discoloured maple leaves with a whitish coating on the shoot.
Discoloured maple leaves with a whitish coating on the shoot.
In this article · 2 chapters
The field maple in its pot in the garden.
The field maple in its pot in the garden.

Infestation in detail.

The affected leaves stand up steeply, remain bent backwards, curl up and gradually dry out from the edge. Whole shoots can wither down to a leaf cluster with small, stunted leaves at the shoot tip.

In addition to the white fungal coating, purple-reddish discolorations are sometimes visible on the leaves.
If the inflorescences are infested, the flowers are no longer fully developed, the petals remain narrow and turn green.
Severe infestation can also result in fruit infestation in susceptible varieties.

The fungus penetrates the inside of the leaf in spring. The spores through which it spreads are usually only formed in summer within the white coating.

Whitish coating on the leaf surface.
Whitish coating on the leaf surface.
Whitish coating and dark edge discolouration on a yellow-green leaf.
Whitish coating and dark edge discolouration on a yellow-green leaf.
Several discoloured and curled leaves on the branch.
Several discoloured and curled leaves on the branch.

Treatment and tool care

The affected leaves must be removed and the bonsai must be treated with a powdery mildew agent. In the following spring, a prophylactic treatment with another powdery mildew agent should be carried out during the new shoots in spring.

Caution: After treatment, clean the tools thoroughly with spirit, otherwise the spores will be transferred to other bonsai.

The whitish-grey coating covers much of the leaf surface.
The whitish-grey coating covers much of the leaf surface.

Three practical tips.

  1. Look closely

    Check young leaves and shoots for a white coating and visible changes.

  2. Remove affected leaves

    Remove affected leaves as described in the article.

  3. Clean your tools

    Thoroughly clean the tools used after finishing the work.