The odium, or
Under the name of cryptogams are hidden (this is also the etymological origin of the word) microscopic fungi, whose development is favored by moisture. The diseases they cause (fungal infections) hinder the development of all cultivated plants. The rose is particularly sensitive to six of these diseases.
Also called White, this disease results from attacks of a fungus of the family of Erysiphaceae Sphaerotheca pannosa, which manifests itself from the first heat in the form of a white down gradually covering the entire plant. This very disgraceful disease considerably harms the development of the plant, the mycelium taking directly into the cells of the plant.
Climbing roses are particularly susceptible to powdery mildew, whose spores vegetate in dormant buds. A nitrogen excess, which promotes the rapid growth of vegetation, is also conducive to powdery mildew.
The fight against powdery mildew begins with a selection of roses, especially in humid climates and particularly hot summers. There are many products on the market, allowing curative or preventive treatments of powdery mildew. These are, in all cases, fungicides based on sulfur, karathane, dinocap, diphenyl crotonate. Effective curative treatment must nevertheless be followed by regular treatments, because powdery mildew is again very easily (like all mushrooms) once it finds favorable conditions for its development. A good precaution will also be to avoid wetting foliage during watering.
Rust results from attacks of a mushroom from the family of basidiomycetes, Phragmidium subcorticium, which causes the appearance of spots of a brownish orange, then pustules on the inner side of the leaves. These are not slow to fray, then fall. This disease particularly affects botanical roses and old; it sometimes affects contemporary roses. It often comes from a potash deficiency. You will find many very effective anticryptogamic products on the market.
The black spots of rose leaves (or marsonia or black spot) originate from the attacks of a fungus of the family of discomycetes, the Diplocarpon rosae, which are manifested by the appearance of purplish-brown spots on the leaves, causing them to fall prematurely. The disease begins as soon as the rose bush starts to grow in July-August and in the most severe case reaches all the rose leaves. He can lose all his leaves. Despite a radical size, the plant may refuse to bloom for several years. In addition to the curative chemical treatment, care must be taken to collect all the dead leaves and to burn them, the spores vegetating at their level. Avoid mixing with compost, especially if the affected leaves fall on the lawn during the mowing season; in fact the disease would spread the following year through the provision of compost at the foot of healthy roses. Again, some contemporary varieties are significantly more resistant to the disease than older roses. Botanical species are always the first to be affected.
Preventive treatment with a multipurpose fungicide product is usually sufficient. It must be applied as soon as the leaves appear on both sides. For curative treatment, use specialized products based on zineb or sulfur.
The root rot comes from the attacks of a fungus of the family of PyrenomycetesRosellinia necatrix, which readily attacks the vine, fruit trees and many herbaceous plants. The roses do not escape; these attacks affect the roots that they invade a cottony coating and eventually rot. They often result from a contribution of fresh manure, carried out immediately before planting. The risk is even greater on a wet or poorly drained land. The evil is practically irremediableit is necessary not only to tear the affected roses, but to burn them, disinfect the soil thoroughly, or even completely change the soil.
This mold results from attacks of a fungus of the family of discomycetes, otherwise known in eminently sympathetic forms (the morel and the truffles), but much more formidable for the rose bush, the vine and many other floral plants in the form Botrytis. The disease is manifested this time on petals, sometimes on pimples, which fail to flourish. The hot, stormy and humid weather favors its development. In addition to commercial polyvalent fungicide products, captan or thiram sprays are quite effective. Disinfection of the soil before planting is an excellent prevention. In the case of an illness observed during the previous season, preventive spraying must be carried out as soon as the vegetation has recovered.
Rose canker is one of the many forms of this disease bacterial naturewhich affects in comparable forms very many plants. It affects the stems, from the graft to the branches, causing browning of the bark and the appearance of calluses that hinder the progression of the sap. The chancre results here from the development of Coniathyrium fuekelii. Its spread often comes from a bad disinfection of a pruner having served to the size of affected subjects. We must therefore carefully consider the roses at the reception, especially if they come from uncertain sources. There is practically no no cure; the only solution is to tear and destroy by burning the affected plants.
The rose can also be reached by:
- mildew, result of attacks of a mushroom of the family of Phycomycetes: Peronospora. Although not very visible, it impairs flowering by forming small brown spots on the sepals.
Little subject to attacks by virus, the rose bush can in exceptional cases be reached by:
- Mosaicwhich causes lightening of the veins. The leaves gradually cover with yellow mosaic-like spots and stun. There is no other cure for the treatment of virus diseases thantear off the plant reached and the burn.
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