Here you can find out how you can recognize, fight and prevent rust on rose, as well as information on home remedies and pesticides against rose rust.
Rose rust ( Phragmidium mucronatum or Phragmidium tuberculatum ) is one of the most common fungal infections in roses. Infested leaves look ugly and a heavy infestation can reduce the growth of your roses. We will show you how you can recognize, fight and prevent an infestation.
Recognize and determine rose rust
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Do the shoots, leaves, or buds of your roses have small yellow-red spots on the top of the leaves? If the underside of the leaf also shows pin-sized yellow-orange, later black, spore bearings, it is with great certainty that it is the rose rust. In the case of a stronger infestation, which occurs very rarely, premature leaf shedding is also possible on the rose. Affected tissue can be enlarged (hypertrophied) as the plant cells swell.
Rose rust: background information on the harmful fungus
The fungi that trigger the rose rust spread via spores that are transported through the air. Optimal conditions for the fungal spores to germinate are persistent leaf wetness for a period of over two hours and temperatures of around 20 ° C. The mushrooms overwinter as mycelium in the shoots of the rose or as spores on the fall foliage. Incidentally, an outbreak of disease is a little less common than the dreaded black spot ( Diplocarpon rosae ), also known as black spot disease. In addition, rose rust is a more harmless rose disease compared to star soot and usually only causes cosmetic problems due to the unsightly leaf spots.
Rose rust prevention
As with many other fungal diseases, preventing rose rust is a relatively difficult matter. However, if your rose is already infected, there is a trick to prevent new leaf spots or only to a limited extent. You have to know that the fungus overwinters mainly on old fallen leaves. Therefore, the leaves should be collected and disposed of on the compost and then well covered with other organic waste.
An alternative is to work the leaves intensively into the soil. In both cases, soil organisms break down the fungal spores of the rust pathogen relatively quickly and thus render them harmless. If you want to be on the safe side, you can dispose of the infested leaves directly in the residual waste. The location also plays an important role. Here it is important to avoid roses that are too close together and to ensure that they are in a sunny location.
We also recommend that you keep the leaves dry when watering so that the fungal spores do not have the necessary leaf wetness to germinate. In addition, you should avoid planting wild roses in the immediate vicinity, as these are popular hosts of mushrooms. All of this makes life difficult for rust and other fungi.
In addition to these preventive measures, preventive pesticides are also available, for example, agents with the active ingredient medium. It is important to wet the entire plant and the undersides of the leaves. If you want to prevent with home remedies, you can inject field horsetail or nettle tea in critical phases and hope for a preventive effect.
And what about resistant varieties? It’s not that easy to answer. Since rose rust is not one of the most important rose diseases, resistance to it is not as important as, for example, powdery mildew. For this reason, it is often not mentioned at all whether a variety shows resistance to rose rust. However, it is always advisable to buy roses with an ADR seal. In general, these rose varieties have to be particularly resistant to diseases.
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An optimal supply of nutrients to your roses ensures that your plant is less susceptible to harmful organisms such as rose rust. We recommend that you ensure a good supply of potassium and reduced nitrogen fertilization of your roses. With a fertilizer specially tailored to the needs of roses, you can easily achieve an optimal supply. Our organic rose fertilizer offers a perfect ratio of nitrogen to potassium and ensures strong roses over the long term.
Fighting rose rust: Effective sprays
Treatment is not necessary in the case of a slight infestation with rose rust. But if more than a third of the leaves show symptoms, we advise you to react. We also recommend treatment if you can see an infestation nearly every year. In this case, you should pay close attention to an infestation from the beginning of May and treat the rose rust at an early stage.
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Active substances against rose rust are, for example, tebuconazole, azoxystrobin, or difenoconazole. We recommend that you do not use the same crop protection product every year, but rather change the group of active ingredients. Such a change is possible, for example, with the active ingredients difenoconazole and azoxystrobin. Please use the agent according to the instructions for use and only in the shortest possible time, but until the control is completely successful.
If you no longer have any effect after a certain period of time, resistant fungi may have established themselves. Then you should use a plant protection product that comes from a different group of active ingredients. These groups are coded on the packaging of the plant protection products with a capital letter and a number.
A very common pest on roses is aphids. In our special article, we will show you how you can combat aphids on roses in a natural way.