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Hypericum rust

Hypericum rust on St John’s wort is caused by a variant of Melampsora. This fungus primarily affects woody crops.

recognize Hypericum rust
Hypericum rust underside leaf St John's wort, photo: W.N. Ellis - CC-SA 4.0

Hypericum rust (Melampsora hypericorum). Rust on St John’s wort is caused by a variant of the fungus Melampsora. This fungus primarily affects woody crops.
The spores of the fungus hibernate on the fallen leaves. The dead leaves are also the source of renewed infection in the spring. As early as early spring, yellow spots appear on the leaves, which gradually increase in size and clump together to form dark brown spots. Orange fungi form on the underside. The leaves fall off prematurely – sometimes as early as August. Members of the Hypericaceae family are the host plant of this fungus.

Where to find

Control

Trim away infested leaves and twigs; remove fallen leaves (kerbside garden / food waste, not on your compost pile).

Prevention

Plant less susceptible (resistant) varieties and provide good growing conditions. Clean up fallen leaves in the fall.

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