June 10, 2025, 3:13 am | Read time: 4 minutes
The name “rose rust” is quite fitting: Pustules resembling rust on the underside of rose leaves indicate this fungal disease. myHOMEBOOK explains how to distinguish this disease from other fungal infections, how effective prevention works, and what to do in serious cases.
If you have roses in your garden, you likely agree: Fungal pathogens love the most romantic of all flowers. Rose rust (Phragmidium mucronatum) is one of the most common fungal diseases affecting roses, alongside powdery mildew, black spot, and gray mold. We explain here what rose rust looks like, what you can do to prevent your roses from getting sick, and what to do if the disease has already struck.
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Identifying Rose Rust
Rose rust overwinters in the form of hardy spores on fallen leaves and woody shoots. As early as the end of March, the new leaves become infected. Rose rust becomes clearly visible in May when small red-yellow spots appear on the upper sides of the leaves. If the infestation is severe, the spots can merge. On the underside of the leaves, small orange-red, later dark pustules form.
Distinguishing Rose Rust from Other Fungal Diseases
- Powdery mildew causes a white, powdery, easily wiped-off coating on the upper side of rose leaves.
- Downy mildew forms a gray-white fungal mat on the underside of the leaves and leads to yellowish to brownish spots on the upper side.
- Black spot appears on the upper side of the leaves as irregularly shaped, sooty-looking black-gray spots, which may be surrounded by a yellowish halo.
- Gray mold leaves brown, dead spots on leaves, buds, and flowers, which are eventually covered by a mouse-gray fungal mat.
Also interesting: When and how to prune roses correctly
Preventing Rose Rust: 6 Tips for Healthy Roses
There are numerous ways to prevent an infestation with rose rust.
1. Choose robust varieties: ADR roses (tested roses with high resistance) are considered particularly robust and are less affected by rose rust.
2. Choose an airy and sunny location: A sunny spot with good air circulation ensures the leaves dry quickly, making it harder for fungal spores to germinate. Avoid planting too closely together. At the same time, regularly remove shoots growing into the interior of the bush.
3. Targeted watering: When watering, make sure to water at the base to keep the leaves as dry as possible.
4. Do not over-fertilize: Proper fertilization strengthens plant tissue and reduces susceptibility to fungal diseases. Over-fertilization, however, makes plant tissue soft and more prone to diseases.
5. Plant-based strengthening agents: Spraying with, for example, horsetail can strengthen cell walls and support the natural defense against rose rust and other diseases.
6. Maintain hygiene: Quickly remove affected plant parts. Do not compost them, as many garden composts do not reach the temperatures needed to destroy the fungal spores.
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Combating Rose Rust
Whether rose rust should be combated after its outbreak mainly depends on the extent of the infestation. A light infestation can often be managed with proper pruning the following spring, combined with thoroughly removing fallen leaves. Often, rose rust disappears on its own this way. However, if rose rust returns every year or the infestation is severe, targeted treatment can help. No curative biopreparations are available, so organic gardeners primarily rely on preventive measures. Those who wish to use conventional fungicides have systemic agents with active ingredients like azoxystrobin, difenoconazole, or triticonazole available, which specifically kill rose rust. It is important to rotate these active ingredient groups to prevent resistance. Active ingredient groups can be identified by the endings of the active ingredient names. For example, difenoconazole and triticonazole belong to the same active ingredient group and should not be used consecutively.