Hemm diseases of roses they are very common, as the rose is one of the most loved and cultivated ornamental plants in our country. It is therefore easy for pathogens of a fungal nature to attack them, causing diseases that can damage the plants even in a serious way. These pathologies are many and it is not always easy to recognize them.
In this article we see the damage they cause and understand how to prevent them, using agronomic techniques and treatments allowed in organic farming.
What are the diseases of roses
When we talk about diseases of roses, we are making a very broad speech, which can include pathologies of different nature, very distant from each other. Specifically, we could talk about downy mildew, powdery mildew (or bad white), scab, or, again, rust. So let’s see these diseases one by one, so that we can better identify them, and then run for cover, preventing them or treating the infected plants.
Downy mildew of the rose
Hemm downy mildew of the rose (Scattered downy mildew) is a specific disease of roses. It appears mostly in intensive cultivation, with conditions of high humidity and water stagnation. However, it can also occur in domestic crops.
The disease shows its symptoms on the leaves, where chlorotic spots appear. In correspondence with these spots and on the underside, a greyish mycelial felt is formed. The leaves of the plant first deform, then become blistered, later necrotize, dry out and fall off. On the flower the damage is indirect, as the decay delays or completely cancels the opening of the buds, and therefore the flowering.
Powdery mildew or white disease of the rose
"Lpowdery mildew of the rose (Sphaerotheca pannosa) is a disease that develops specific symptoms. For one thing, it has great virulence. It affects all the aerial organs of the plant, especially leaves, buds and flower buds. After an attack, on the affected parts first of all discolored areas are noticed, later, on these areas, a whitish and powdery mold develops. Flowering is impaired, as the buds wither and do not open. On young stems and twigs, powdery mildew causes more or less serious lesions.
The pathogen that causes this rose disease mostly develops in warm, humid environments.
Rose scab
Hemm rose scab (Diplocarpon rosae or Marssonina rosae) is among the most frequent rose diseases. It shows up both in intensive cultivation and in public and private gardens. Its main symptom are blackish spots, with irregular edges, which extend “like a flame” on the upper surface of the leaves. The spots vary in size and tend to merge, causing blackening on almost the entire surface. The final result of the disease is an accentuated defoliation, which compromises the flowers and weakens the plants, which are forced to germinate continuously.
The environmental conditions that favor the scab of the rose are the hot and humid periods, with temperatures around 20-25 ° C, therefore spring and late summer.
Rose rust
Hemm rust of the rose (Phragmidium subcorticum) is perhaps the most common disease of roses. Also in this case, it shows itself on the leaves, where angular and chlorotic spots appear on the underside. From an initial light orange color, the patches then become darker, necrotic. In correspondence, typical pustules are formed, which sometimes suggest the koċinilja. The pustules can join together, drying out the leaves. In any case, the affected leaves fall off, leaving the plant bare. The consequences, in addition to the aesthetic damage, are a minimized and delayed flowering. Furthermore, the plant gradually weakens, stopping its growth. Again, the disease appears in mild and humid periods.
How to prevent rose diseases
After describing the main diseases of roses, let’s see how to defend plants with agronomic prevention. In this sense, first of all, one is important correct pruning of roses. In this way we keep the plants luxuriant, stimulating the emission of new shoots, in practice we rejuvenate them. In addition, pruning has the effect of aerating the foliage, thus avoiding the formation of stagnation of humidity inside, which could cause fungal pathogens to take root.
Another recommendation is to eliminate pruning waste around the plant. Dying vegetation is the ideal environment for fungi to proliferate. This is all the more true if we are pruning diseased plants, where we are going to eliminate the affected parts. In this case, the best solution would be to burn the pruning waste (according to the provisions of the legislative decree 6/4/2006 n. 152, article 182).
Organic products for the fight against rose diseases
To prevent the rose diseases described above, gods can be used products allowed in bio. For example, immediately after pruning it is good to carry out a treatment with gods cupric salts (like these). These are organic products that can be purchased without the license for phytosanitary products. For dosages, follow the directions on the label.
With the arrival of spring, the best environmental conditions for an attack of fungal pathogens occur. In this season, therefore, an excellent preventive product, also allowed under the organic regime, is wettable sulfur (found here).
Finally, an even simpler preventive treatment is the bikarbonat tas-sodju (dosage: 10 g per 1 l of water). When dissolved and sprayed on the leaves in the evening, it creates an inhospitable environment for fungi and, therefore, avoids diseases.
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