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The parasites of roses
Roses are among the most widespread plants in gardens and terraces throughout Europe; much of this success is due to the spectacular blooms, which have made this flower popular, even as a cut flower, for bouquets and bouquets, full of symbolic meanings: the rose has always been the flower of lovers. Another reason that makes roses as interesting as garden plants is undoubtedly the ease of cultivation; even a novice gardener can grow them successfully, obtaining abundant blooms and healthy and vigorous plants.
Even the most experienced hobbyists, and even the nurserymen themselves, may experience minor inconveniences, due to various causes, from the most common insects, to the climate or to deficiencies of particular chemical elements. We therefore examine the main threats to our roses, so as to keep them healthy over time.
Oidium (Sphaerotheca pannosa)This fungus develops circular spots, quite large, with a dusty appearance, white in color; it is generally called white mal and develops on the leaves and on the chalice of flowers. Generally the damage is only aesthetic, although massive infestations can cause the buds to not open and the leaves to curl up. Powdery mildew develops mainly in spring and autumn, characterized by cool nights and very hot days, with high humidity. It is weakened with the use of specific fungicides, generally based on sulfur; sodium bicarbonate treatments are also effective, to be repeated weekly.Punctuation (Diplocarpon rosae)Also called black spot this fungal parasite develops thick dark, black or purple spots on the leaves and on the stems; often infestations are such as to cause the leaves to turn yellow, with consequent fall. It develops mainly during the summer months. Sulfur or triforine fungicides are used against scab. To prevent the spread of the disease it is good to remove the sick leaves and stems, and also the fallen leaves, which will be destroyed.Rust (Phragmidium)These are reddish, sometimes dusty, even bright orange spots that develop on the underside of the leaves and sometimes even on the stems. It is prevented and treated with sulfur-based fungicides. To prevent rust it is advisable to remember to remove all the foliage of spring prunings, as these mushrooms winter on fallen leaves.MildewFungal disease with rapid development: the leaves turn yellow and dry dramatically, the young branches and floral goblets are covered with reddish or dark marks; downy mildew develops mainly in a very humid climate with fairly low temperatures. To prevent the development of downy mildew it is good to put the roses in a well-ventilated place and not too thick; to treat infected plants it is good practice to start by removing the infected tissues, then treatments with Bordeaux mixture or cupric products are practiced.Botrytis (Botrytis cinerea)Very common especially in potted roses and nurseries, this fungal disease develops blotchy, felty, greyish, dusty-looking patches, generally followed or preceded by the blackening of buds and small stems, which tend to rot and deteriorate very quickly. To prevent the development of botrytis it is good to put the roses in a well-ventilated place, avoid water stagnation. The damaged parts are removed, therefore copper-based treatments are practiced.Anthracnose (Sphaceloma rosarum)On the leaves small pink, purple or red spots spread, which tend to discolor, generally leaving holes on the leaf blade; subsequently the foliage dries up and falls. Anthracnose develops in areas with poor drainage and high humidity or water stagnation. In case of illness sulfur-based treatments are practiced.Cranial cancerThis definition indicates several fungal parasites that spread through the lesions caused on the stems by other fungal diseases or pruning. It is good practice to remember to clean the tools used during pruning, both before starting, and during the passage from one plant to another, to limit the spread of this type of pathogens. Generally they appear as very obvious spots along the stems, also characterized by deep marks, hump or lacerations of the bark. The only truly effective "cure" consists in removing the infected stems and in the consequent destruction of the same.Nutritional deficiencies
Roses are very generous and vigorous shrubs, which produce a large amount of new vegetation every year; over time they tend to exploit the soil a lot, facing very evident nutritional deficiencies. A good semi-annual fertilization is essential, but often there may be cases where further interventions are necessary, sometimes even based on microelements.
Excess calcium in the soil, low amount of iron and very high soil pH values can cause the development of ferric chlorosis. Gradually the leaves turn yellow, to completely discolor; plants affected by ferric chlorosis tend to develop stunted and produce few flowers.
The leaves of poorly fertilized roses tend to be opaque, yellow-green, progressively lighter.
Plants that suffer from this deficiency tend to have very damaged leaves, with dark, often dry, zoning; the color is off, gray-green.
In addition to scarce blooms this deficiency over time is manifested by the yellowed leaf tips, often dry, and can also lead to the loss of the leaves.
The leaves become gray-greenish, tend to dry and discolor at the edges, progressively starting from the outer leaves.
the veins tend to turn yellow, on the leaves there are light or dry zoning, often the buds are stunted.
Plants grown in soil free of zinc have deformed leaves, greenish-yellowish, thin and elongated.
Leaves with striking green veins with a page that gradually turns yellow and dries. The excess of manganese instead manifests itself with small black spots spread over the entire leaf page.
In cultivation we note that sporadic contact with small doses of herbicide, such as glyphosate, can cause various types of damage, such as yellowed leaves and bizarre-shaped flowers, which often bloom with very short and matted petals. Practicing weeding is good to be careful to avoid the leaves of the shrubs; moreover it is always advisable to avoid spraying the herbicide during windy or very hot days. The damage caused by herbicides are generally mild, and only damage the flowering immediately following the damage itself, so they do not last over time.
Sometimes roses have poor growth, both in the single year and over the course of several years, they produce short and stunted stems, they bloom poorly, without having other striking symptoms. This behavior could be due to irregular watering and occurs above all in potted specimens. Excessive watering, with soil soaked in water, leads to the suffocation of the roots, which therefore are not able to supply the plant with nutrition; in the same way, poor watering, especially during dry periods, can quickly lead to desiccation of the plant. Poor or excessive watering continued over time leading to the drying of leaves and branches, and therefore of the entire plant. Incorrectly watered plants are also more sensitive to the attack of various types of diseases.
Stunted growth can also be due to scarce or no fertilization: let us remember to fertilize our plants, in autumn or at the end of winter, with organic fertilizer; in June we can repeat the fertilization, perhaps using a slow release fertilizer with the addition of microelements.
Most roses need good lighting for a balanced development, the ideal place is full sun. Plants grown in the shade generally produce few flowers, have very long stems and few leaves, which also grow small; sometimes it can happen that the plants grow in the direction of the light, assuming a posture completely bent to one side.
Mosaic of the rose
It is a virus that causes streaks on the leaves, elongated or rounded, yellow or green; the plant has a rapid decline, with a lack of flowers and new shoots. Generally, as with most viruses, mosaic plants quickly perish, until they die. There is no cure for this virus, it is therefore necessary to eradicate the diseased rose and replace it with a healthy one. There are varieties of roses particularly resistant to the mosaic virus.
Rose pests: Natural remedies against rose lice
It is not always necessary to use chemical products to counter the spread of the most common rose pests, or aphids, commonly known as lice. These insects feed on the youngest and tender parts of plants and can spread very quickly, so as to quickly cover both the leaves and the stems and buds.
A natural remedy very effective to safely and quickly eliminate the problem is to boil garlic in water, then going to filter it and vaporize it on the infested plants. The quantities can be of a head of garlic divided into segments per liter of water. The infusion should be boiled for at least five minutes before being filtered and vaporized. It is also possible to prepare a nettle macerate, for which the entire plant is used, commonly found in lawns and gardens. The proportions are 1 kg of freshly harvested nettles or 200 grams of dried leaves per 10 liters of water. It would be better to use rainwater and a container that is not metallic. To get the macerate, the nettles must remain in soak for about 15 days, leaving the container open, perhaps protected with a net to prevent dirt or insects from entering it. This product, once filtered, will be diluted before being used, calculating a proportion that varies for one liter of macerated water from 10 to 20 liters.
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