Rust stains on a leaf
Traces of rust on the underside of a leaf
Rust on the leaves of a rose bush
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Rust disease: causes, symptoms and treatments
A disease caused by micro-fungi, rust has aesthetic consequences. However, it can weaken plants, slow their development and limit their productivity.
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Find all our tips in the application
Rust is a fungal disease, like moniliosis and powdery mildew. The term refers to a family of diseases caused by parasitic Puccinia spp. fungi, which belong to the order Pucciniales.
It takes its name from the change in appearance it causes when it attacks a plant.
Rust disease generally affects plants at an advanced stage of growth. It targets aerial parts, mainly leaves, and to a lesser extent stems and buds.
Contributing factors
Many species of vascular plants, including houseplants, are affected by rust. Roses, carnations and marigolds are the most likely to be affected. In the vegetable garden, asparagus and peas are particularly vulnerable. Trees such as birch and plum should also be monitored.
Plant rust occurs almost year-round. Spring, summer and early autumn are particularly at risk because of the weather. Humidity and intense heat favor the onset of the disease. Indoors, poor ventilation represents a danger.
Finally, previous contamination is an additional factor, as not all pathogens may have been eliminated.
Finally, previous contamination is an additional factor, as not all pathogens may have been eliminated.
How it works
The fungus emits spores that spread over the aerial parts of plants. They are carried by the wind into your garden, living room or vegetable patch. Wind also facilitates transmission from one plant to another.
Sometimes, an attack of rust comes from parasites that have spent the winter in the humus, among plant debris. When spring comes, they start to spread again.
Symptoms
Plant rust is most noticeable on the leaves. The upper surface of the leaf blades shows yellowish spots, which may turn orange or red. White or brown pustules form on the underside, stems or buds.
The color of the aureoles or necroses varies according to the type of rust and the variety concerned.
The disease does not kill crops, but it does have aesthetic consequences. An attacked leaf is weakened and eventually falls off. The plant produces fewer flowers and fruit, as photosynthesis is slowed down.
Treatment
To prevent rust and stop it spreading, spray the foliage with a decoction of garlic or horsetail slurry. Remember to clean and disinfect your tools (pruning shears, shears) so that they don't transmit the disease.
Limit conditions favorable to rust development. Place your plants in an airy environment, without excessive heat or humidity. Water preferably in the morning or evening, targeting the base rather than the foliage.
A fungicide treatment is recommended in most cases. Bordeaux mixture is the remedy most often used by gardeners to combat rust disease.
As soon as you notice the infection, cut off and destroy all affected leaves.
