Colorful and exuding a delicately aromatic fragrance – roses are among the most important and diverse woody plants that are cultivated in Germany’s gardens. Properly cared for and optimally watered, the popular plants thrive in every green area. But the “Queen of Flowers” ​​also shows susceptibility to various diseases and pests, which can be felt, for example, through mold, fungal diseases or viruses. The leaves and buds are particularly often affected, and they then tend to discolour or to expectorate. But if targeted remedial action is taken, even beginners can get a good grip on rose diseases.

Fungal attack on roses – powdery mildew

Roses are particularly often affected by various fungi. Powdery mildew is known above all, which is a hose fungus that spreads on the surface of the plant and penetrates the cells with special suction organs. There important assimilates are withdrawn from the infected roses. Powdery mildew in particular shows the following symptoms:

  • In spring and summer the rose petals are covered with whitish or gray spots; the fungus is still in the early stages.
  • If a floury-moldy layer can be seen on and under the leaves, on the buds, flowers and fruits, rose disease has reached the second stage.
  • Later, the leaves will curl up while the flowers will not open and the rose will wither.
  • If the powdery mildew is discovered late, the brownish discoloration of the pavement will already appear.

Powdery mildew is usually favored by incorrect care. Particular care should be taken to ensure that sufficient space is left between the individual plants when planting roses. A high nitrogen fertilization and high temperature fluctuations can also promote fungal attack. Unlike most other fungal diseases, powdery mildew does not spread best in damp weather, but rather in warm, dry conditions. Therefore, the strongest infestation can be observed in late summer and early autumn.

In order to be able to combat powdery mildew effectively, the infected parts of the plant must be removed in good time; this also applies to fallen leaves and plant remains. If there is already a strong infestation, special fungicides can also be used, for example lecithin preparations that are gentle on beneficial organisms or sulfur agents, which are considered to be relatively environmentally friendly. So that the rose does not become infected with the fungus in the first place, special precautions can be taken: One-sided fertilization with high amounts of nitrogen and too close planting should be avoided. If high-pressure weather is announced or there are strong temperature fluctuations, garlic broth or plant strengtheners can be introduced as a preventive measure, which make the crop more resilient overall.

Wrong mildew

In contrast to powdery mildew, which is characterized by the infestation of pouches, downy mildew is caused by algae fungi. These live between the cells inside the plant and from there form whitish gray or brown velvety coatings that show up on the underside of the leaves. On the other hand, brown or purple spots form on the upper side of the leaves, some of which also affect the flowers. In contrast to powdery mildew, this rose disease mainly develops in a moist environment, but is also favored by high nitrogen levels. Systemic fungicides, which are absorbed through the roots and leaves, have proven to be particularly effective in combating the fungus.

However, powdery mildew and downy mildew can also be treated with the help of tried and tested home remedies. Various mixtures can be given over the roses with the help of a spray bottle:

  • Combating the current infestation and preventing it at the same time is achieved with a mixture of one part water and one part milk.
  • Starch garlic stock is made from half a liter of boiling water and 3 small cloves of garlic.
  • Table salt also helps: a mixture of half a teaspoon of table salt and one liter of water also curbs the spread.

The very effective horsetail broth with its high silica content ensures that the firmness of the cells on the leaf surface is increased, so that the fungal spores can no longer easily penetrate the leaf. Overall, infections are made more difficult or even prevented with the help of the broth. The broth is easy to make: 750g fresh field horsetail or 100g dried plants are needed for the mixture. Only the summer shoots that are cut close to the ground should be used. The horsetail is then added to five liters of rainwater and left to stand for a total of one day. Then the mixture is boiled for half an hour, strained and diluted with water in a ratio of 1: 5.
As a preventive measure, the horsetail mixture can be given every three weeks; if there is an acute infestation, it should be administered every other day.

Tip: Chives, chervil or basil should be planted between roses that are threatened by powdery mildew.

Treat fungal diseases effectively

In addition to powdery mildew and downy mildew, rose plants are also often attacked by rose rust, star soot or gray mold. The rose rust, which occurs particularly frequently, is a fungus that overwinters with blackish spores on the fall foliage. In spring, the new infection takes place and it spreads via summer spores, which are formed in the yellow pustules on the underside of the leaf. From May yellowish to reddish spots can be seen on the upper side of the leaves. The underside of the leaf also shows clear symptoms of fungal attack: reddish to yellow pustules can be seen here at the beginning, later reddish brown, and finally dark pustules in autumn. The fungus leads to premature leaf fall. The plant as a whole is significantly weakened by the drastic loss of leaves. In order to be able to fight the rose rust effectively,

  • Completely remove infected leaves in summer
  • In autumn, make sure that infested fallen leaves are no longer a source of infection
  • If an infection occurs repeatedly, spray fungicides, some of which are also effective against powdery mildew and star soot.

However, various preventive measures can help so that the roses are not attacked by the fungus in the first place. This includes regular thinning and targeted cutting of the plants, and balanced, potash-based fertilization. Watering should not be done in the evening and, above all, care must be taken not to wet the leaves. In spring, repeated administration of plant strengtheners or horsetail broth helps to make the plant more resistant.

These measures also help if the flowers are infected with rose rust. The disease is easy to spot; in the event of an infestation, the leaves show small, round spots of brown to black color with a radiant edge from May onwards. The leaves turn yellow prematurely and lead to premature waste. This fungus can also overwinter on the fallen leaves without any problems, which is why a complete removal of the fallen leaves is of great importance.

In addition to rose rust and star soot, roses are particularly often attacked by gray mold. Rosen disease is caused by the harmful fungus Botrytis cinerea, which is widespread in numerous species around the world and which overwinters in the form of small permanent bodies on dead plant parts. An infestation with gray mold manifests itself in the formation of mouse-gray fungal lawns, which are very dusty. The buds and leaves of the roses are particularly affected; in addition, flowers and buds become soft and rotten quickly. With high humidity and warmth, the fungus spreads strongly.

As a preventive measure, an airy location with a permeable soil has proven its worth. In addition, care should be taken that the roses are not planted too densely and that they are thinned out regularly. During irrigation, the leaves should not be wetted with moisture as far as possible, as damp parts of the plant promote the spread of the fungus. Regular loosening of the soil can also reduce the infestation of gray mold. The roses should be fertilized with a caliber emphasis, with caution when using nitrogenous fertilizers.

As with the other fungal diseases, various plant strengtheners have proven effective as a preventive measure; In addition to horsetail extracts, this also includes various rock flour. If the plant is infected, the diseased parts must be removed immediately. An approved fungicide must be used very early or, preferably, as a preventive measure, if experience has shown that gray mold occurs frequently.

Tip: It is best for beginners to use particularly resistant rose varieties, for example Red Yesterday or Ricarda.

Viral disease of the rose

The so-called “mosaic disease” is one of the most common virus diseases in roses, which appear on the leaves through yellowish discoloration of the edge of the leaves and red mosaic spots in the form of rings or ribbons. The infestation can also be recognized by the soft, wavy leaves that are formed by the virus. The transmission is presumably done by ooculation. If the roses are infested, they will develop very slowly. The formation of the flowers is also disturbed, which overall remain quite small. Infested plants tend to shed their leaves prematurely; this weakens the rose even more, which can be shown in a higher susceptibility to other rose diseases or pests. If the plant is infected, it can no longer be saved. To prevent further spread,

Rose diseases due to insufficient supply

Roses must always be supplied with sufficient nutrients. For example, if the plant suffers from iron deficiency, symptoms of chlorosis, also known as yellowness or bleaching, will show up. This is a flat yellow or whitish lightening of the leaves, which occurs due to the lack of production of the plant pigment chlorophyll. The leaf veins usually remain green, while the rest of the leaf brightens overall. The inadequate supply can be due to various causes:

  • Chlorosis is particularly common when the soil is too calcareous.
  • Even with excessive compaction of the substrate, leaf lightening can occur more frequently.
  • Drought also plays a role; Permanently moist soils can promote the development of chlorosis.

In the long term, the only thing that helps against chlorosis is to improve the properties of the soil, so that the rose can thrive again optimally. Loose substrate mixtures are best suited. It is important that the roots have enough space underground to develop. This ensures that sufficient nutrients can be absorbed through the root tips. Soil that is not too cold and rich in humus, which does not tend to waterlogging, is particularly suitable for planting roses.

Roses are among the most popular plants that should be in every home garden. The fragrant flowers are suitable for passionate hobby gardeners as well as for plant lovers who have not yet gained so much gardening experience. However, since roses are generally quite susceptible to various diseases, beginners should resort to the robust varieties. – Then the joy of the “Queen of Flowers” remains undimmed for a long time!

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