Roses are thorny shrubs and shrubs of the rose family. 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 many hybrids and cultivars. Easy to live with, they come 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 marsonia of the rose bush
This cryptogamic disease is responsible for pathogenic fungi, Marssonia rose et Diplocarpon rose. Symptoms usually appear in the spring. The marsonia of the rose is manifested 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 leads to a slowdown in the growth of the rosebush.
Treating and Preventing Black Spot Disease
Between May and September, every three weeks, sick roses should be treated 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.
Powdery mildew or powdery mildew
The pathogen of powdery mildew is the fungus Sphaerotheca pannosa var. roses. The signs of this cryptogamic disease can be observed from March until November, in the form of a white felting appearing on the leaves, twigs, flower buds that dry up. Foliage drops prematurely.
Treating and preventing powdery mildew
It is necessary to remove all parts affected by powdery mildew and then burn them. Potash permanganate is then applied as a spray. To prevent powdery mildew, sulfur-based products are effective.
The pathogenic fungi responsible for rust are Phragmidium mucronate et Phragmidium disciflorum. The upper surface of the rose leaves is covered with yellowish spotsand the underside of pustules first orange then brown. In the event of heavy infestation, early leaf fall is quickly observed.
Treating and preventing rust in roses
All contaminated leaves should be removed. You can then treat either with a decoction of horsetail or with a commercial fungicide. As a preventive measure, it is advisable not to wet the leaves when watering and to spray nettle manure three times, one application every two weeks.
The culprit of this fungal disease is Scattered downy mildew, a fungus with a non-cellular mycelium, i.e. an Oomycete. Symptoms caused by downy mildew are quite similar to those caused by marsonia or black spot disease. In fact, we observe brown and/or yellowish spots on the upper side of the leaves of the rosebush. The color of the spots gradually changes, forming a sort of mosaic purple, black and red.
As for the underside of the leaves, it is covered with a greyish felting. Mildew causes defoliation and sometimes even a canker on the twigs and necrosis at the level of the lesions or even an abortion of the flower buds.
Treating and preventing rose blight
It is necessary to eliminate all the branches affected by mildew and, to avoid contaminating the other plants, they must be burned rather than put in the compost. A fungicide marketed in garden centers is then applied or liquid manure is prepared by macerating plants with an antifungal action such as bracken, horsetail or nettle. As for Bordeaux mixture, it is frequently used in the garden for its preventive action against mildew.
Various plant pathogens can cause rose canker, namely Macrophoma, Botryosphaeria, Coryneum or the mushroom Coniothyrium fuckelii. The wounds caused during the pruning of roses encourage the penetration of parasitic fungi into the plants. The fabrics located under the bark are then necrotic. A more or less black canker is observed on the stems, and in the most serious cases, the roses do not survive not to disease.
Treating and preventing rose canker
Bordeaux mixture can treat the disease. To prevent rose canker, Bordeaux mixture should be applied just after pruning and then put a healing mastic on the wounds of the rose.