What are the main diseases of the rose bush? How to treat?


Roses are thorny shrubs and shrubs of the Rosaceae. Vigorous, easy-going, very floriferous and with decorative fruits (rose hips), they are among the most cultivated plants in the pleasure garden. Genre Rosa has nearly two hundred species of roses and there are also multiple hybrids and cultivars. Easy to live with, they are available in such diversity that you can easily enhance your outdoor space with roses of all shapes and colors that bloom from June until frost. But you still have to be vigilant, because no one is immune to cryptogamic or fungal diseases of roses. Let’s see which are the most common and take stock of the treatments and prevention solutions.

Black spot disease or rose marsonia

This fungal disease is responsible for pathogenic fungi, Marssonia rosae and Diplocarpon rosae. Symptoms usually appear in the spring. Rose marsonia manifests itself by black stains that appear on the leaves. These turn yellow and then fall off. The defoliation can be very important and a severe infestation causes a slowdown in the growth of the rose bush.

Treat and prevent black spot disease

Between May and September, every three weeks, it is advisable to treat diseased roses with a mixture of 10 liters of water and 1 liter of horsetail manure or nettle manure which is applied by spraying. To prevent black spot disease, a sulfur-based product such as Bordeaux mixture can be used.

The white of the rose or powdery mildew

The pathogen of powdery mildew is the fungus Sphaerotheca pannosa var. rosae. Signs of this fungal disease can be seen from March through November, in the form of a white felting appearing on drying leaves, twigs, flower buds. The foliage falls prematurely.

Treat and prevent rosebush powdery mildew

It is necessary to remove all the parts affected by powdery mildew and then burn them. Potash permanganate is then applied as a spray. To prevent rose powdery mildew, sulfur-based products are effective.

Rosebush rust

The pathogenic fungi responsible for rust are Phragmidium mucronatum and Phragmidium disciflorum. The upper surface of rose leaves is covered with yellowish spots, and the underside of pustules first orange then brown. In the event of a heavy infestation, we quickly notice the early fall of the leaves.

Treat and prevent rust in roses

All contaminated leaves should be removed. It can then be treated either with a decoction of horsetail or with a commercial fungicide. As a preventive measure, it is advisable not to wet the leaves during watering and to spray nettle manure three times, at the rate of one application every 15 days.

Downy mildew of the rose bush

The culprit of this fungal disease is Peronospora sparsa, a fungus with non-cellular mycelium, that is to say an Oomycete. The symptoms caused by late blight are quite similar to those caused by marsonia or black spot disease. There are indeed brown and / or yellowish spots on the upper surface of the leaves of the rose bush. The color of the spots gradually changes, forming a kind of mosaic purple, black and red.

As for the underside of the leaves, it is covered with a grayish felting. Downy mildew causes defoliation and sometimes even canker on twigs and necrosis on lesions or abortion of flower buds.

Treat and prevent rose blight

It is necessary to eliminate all the twigs affected by mildew and, to avoid contaminating other plants, they should be burned rather than put in the compost. A fungicide marketed in garden centers is then applied or else a liquid manure is prepared by macerating plants with antifungal action such as eagle fern, horsetail or nettle. As for Bordeaux mixture, it is frequently used in the garden for its preventive action against mildew.

Rose canker

Various phytopathogenic agents can be the cause of rose canker, namely Macrophoma, Botryosphaeria, Coryneum or the mushroom Coniothyrium fuckelii. The wounds caused during the pruning of roses promote the penetration of parasitic fungi into plants. The fabrics located under the bark are then necrotic. There is a more or less black canker on the stems, and in the most serious cases, roses do not survive not to disease.

Treat and prevent rose canker

Bordeaux mixture is used to treat the disease. To prevent rose canker, apply Bordeaux mixture just after pruning, then apply a healing mastic to the wounds of the rose bush.