Diseases of roses
Diseases of roses
Roses, delicate and beautiful plants, can be affected by various diseases. The agents responsible for diseases of roses can be fungi, insects, viruses, but also trivial cultivation and pruning errors, which lead the way for viruses or other pathogens to enter the plant. The diseases of roses are fought mainly with preventive strategies, to be implemented when the plants are still healthy and young, but also with chemical means if the same diseases are too widespread or overt. Otherwise, especially for diseases caused by viruses, it is necessary to completely eradicate the affected roses, replacing all the soil. Unfortunately viral diseases, for roses as well as for humans, are incurable, but if the latter often manages to overcome the infectious phase (see the influences) the same cannot be said for roses, which progressively impoverish throughout. their structure.
Fungal diseases are caused by fungi or ascomycetes which carry out parasitic survival on the plant structure of roses. The most feared and most widespread fungal diseases in roses are: gray mold, rot, white sickness, rust, downy mildew and scab. All these diseases are caused by fungi, which multiply thanks to favorable environmental conditions, such as heat and excessive humidity. The fungal diseases of the rose begin to make their appearances during the beginning of summer, becoming particularly infesting and widespread as soon as temperatures exceed 25 degrees and humidity rises to 80%. Muggy, humid, and rainless days can be fatal for roses. Gray mold is caused by the botrytis cinerea fungus, which attacks all parts of the plant. The disease presents with powdery gray spots that can also lead to the drying and folding of the buds. The rot is caused by several species of fungi, which reproduce in conditions of water stagnation. With this disease we witness the rotting of the roots of the roses and the collar of the entire plant, which slowly turns yellow and then dries up. Sickness, also called powdery mildew or white mold, is caused by a strain of ascomycetes belonging to the genus oidium. The disease occurs with the formation of a white powdery layer, which can spread over the whole plant, even if it is found mostly on the buds or leaves of younger roses. Rust is caused by the fungus Phragmidium subcorticium and manifests itself with yellow spots on the upper side of the leaves and powdery patches, always yellow, on the underside. Rose blight is caused by the Peronospora spread fungus, which causes purple, dark, or reddish spots on the upper pages of leaves. Another fungus, Diplocarpon rosae, causes black spots on the rose's younger leaves and petioles. This is the scab, also called "black spot". Fungal diseases of roses are prevented by avoiding water stagnation and excessive heat conditions. Some fungal diseases, such as powdery mildew, can be eradicated with the rain, which is why during the hot season it is advisable to irrigate the roses from above. In case of overt disease, specific or broad-spectrum antifungals must be used.
Parasitic insects also prefer roses, which naturally cannot do anything but host them, accusing phenomena of stunted growth or leaf malformation. Among the parasites of the roses we remember the leafhoppers, the aphids and the red spider. The leafhoppers, as the name implies, are very similar to small green winged cicadas. The name of these insects is Typhlocyba rosae. Leafhopper infestation occurs on the leaves and shoots, which appear lighter in the central part. They prefer rose buds and sprouts, aphids, also called "plant lice". With their pungent mouthparts, aphids suck the sap of roses causing the deformation of the flower parts and blocking their growth. The spider mite is an insect belonging to the mite family. This insect attacks the leaves, causing them to yellow and curl. On the lower part of the leaf margin you can also see cobwebs, which are a clear sign of the presence of the mite. Insect diseases are fought with specific products. Leafhoppers can be eliminated with pyrethrum-based products, while aphids require the use of products that act only on them. The red spider can, however, be removed manually by cleaning the leaves with a soapy cotton swab.
Sometimes, fungi, parasitic insects or cultivation errors, can favor the proliferation of viruses that can cause deadly diseases to roses. One of the most dangerous virus diseases for the rose is mosaic. This pathology attacks the leaves, which take on a yellowish color, with patches similar to a mosaic. The spots do not appear on the flowers, which, however, do not grow or tend to deform and appear smaller than normal. There is no cure for viral rose diseases. If the plant is affected by a virus it is best to eradicate it and completely replace the soil on which it was grown.
Diseases due to crop errors
Errors in fertilization, pruning, watering, can damage roses more than actual pathogens. If the fertilizers are not correctly dosed, symptoms of mineral excess or deficiency can occur on the plant. The excess and deficiency of minerals can also occur on soils not suitable for the rose, soils on which amending fertilizers must be applied. The rose is easily affected by iron deficiency, accusing the symptoms of chlorosis. This pathology manifests itself with leaf yellowing, due to the plant's inability to synthesize chlorophyll correctly. It is known, in fact, that iron intervenes in the metabolic processes that allow the plant to produce chlorophyll, which is the substance that gives the leaves the green color. In the rose, pruning errors, such as inaccurate cuts, can cause wounds that are difficult to heal, resulting in the entry of viruses and bacteria. Excessive watering of the plant can also cause rot, while insufficient watering can cause the branches to dry out.
Diseases of roses: how to prevent and treat them
- January 27, 2021
- Published by My Green Help
Roses are plants that need scrupulous care to vegetate properly and give exceptional blooms every year. Unfortunately, rose diseases can also affect specimens of an experienced gardener, but most of the time they are the result of poor maintenance.
To reduce the risk of diseases it is of fundamental importance to follow the cultivation rules! You can follow these rules by reading our article Rose cultivation: The rules to follow
There are many diseases that can affect a rose plant, below we propose the most frequent and the related remedies:
What are the causes of rose rust?
Rose rust is, as we have said, a disease caused by a fungus, but to develop and create its dangerous molds it needs the right climatic and environmental conditions.
In this sense, excessive humidity is temperatures that are too high (especially in spring), they favor the inoculation of spores, which remain hidden at the base of the rose garden (in the midst of dry leaves that may not have been eliminated well) throughout the winter.
Another great cause of the spread of rust is excessive irrigation: mold, in fact, finds a precious ally in water stagnation.
The aphids (or lice) of roses
Aphids, scale insects, cetonias and red spider mites are the main parasites that can grip the roses. How to recognize their presence? They suck parts of the plant causing the leaves to curl and with reproduction they can completely cover the stems and the bottom of the leaves.
One of the most frequent natural remedies is that related to predatory insects like the seven-point ladybird, which can devour up to a hundred aphids a day. Infested leaves can be cleaned with a moistened cotton swab (in the case of aphids) or soaked in denatured alcohol (in the case of mealybugs). Cetonie and red spider are instead identifiable with the naked eye and can be removed manually.
Powdery mildew (or white disease) of roses
The bad white, Also known as powdery mildew of roses, makes its appearance in spring as a fungal disease that attacks the shoots. A kind of white mold on roses and leaves that curl up, turn yellow and finally dry up. In the case of the first stage of the disease, the natural treatment with bicarbonate sodium: 30 g diluted in a liter of water, with the compound that is sprayed on the affected parts of the plant. Alternatively, numerous products are available on the market, extremely effective.
Scab of roses
There scab is one of the most common diseases of roses. It stands out for the yellowing of the leaves of the roses and the appearance of black spots. It is generally caused by excessive humidity or incorrect watering, combined with spring or autumn temperatures. The black spots reach a diameter of about one centimeter, while the affected leaves turn yellow and dry quickly. It is necessary to act with the appearance of the first black spots on the leaves, using a copper-based antifungal to be performed weekly, until the symptoms disappear.
Rust of roses
Rust is a fungal infection that attacks roses, causing the appearance of rust-colored spots on the leaves. It is a very frequent disease, especially in the spring period. When the first spots appear, the first thing to do is to remove all the affected leaves. Then, carry out treatments with natural remedies or specific products. For example, you can use natural garlic-based infusions: boil 3 heads of garlic in 10 liters of water, let it cool and pour the mixture into the ground.