Here you can find out how to recognize, fight and prevent rose rust, as well as information on home remedies and sprays 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 stun your roses. We'll show you how to spot, fight, and prevent an infestation.
Detect and determine rose rust
Do the shoots, leaves or buds of your roses have small yellow-red spots on the upper side of the leaves? If the underside of the leaf also shows pin-sized yellow-orange, later black spore deposits, it is almost certainly rose rust. In the case of a stronger infestation, which, however, occurs very rarely, the rose can also drop its leaves prematurely. Affected tissue may be enlarged (hypertrophied) as plant cells swell.
Rose rust: background information on the harmful fungus
The fungi that cause rose rust spread via airborne spores. Optimal conditions for the germination of the fungal spores are persistent leaf wetness for a period of more than two hours and temperatures of around 20 °C. The fungi overwinter as mycelium in the shoots of the rose or as spores on the fallen leaves. Incidentally, an outbreak of the disease is observed somewhat less frequently than the dreaded black spot (Diplocarpon rosae), also known as black spot disease. In addition, rose rust is a harmless rose disease compared to blackspot and usually only causes cosmetic problems due to unsightly leaf spots.
Rose rust Prevention
Preventing rose rust is - as with many other fungal diseases - a relatively difficult matter. However, if your rose is already affected, there is a trick to ensure that no new leaf spots appear, or only to a limited extent. For this you need to know that the fungus grows mainly on old fallen leaveshibernates. Therefore, the leaves should be collected and disposed of on the compost and then well covered with other organic waste. An alternative is the intensive incorporation of the leaves into the soil. In both cases, soil organisms break down the fungal spores of the rust pathogen relatively quickly, rendering 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 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 for the fungi. All this makes life difficult for the rust fungus and other fungi as well.
In addition to these preventive measures, preventive plant protection products are also available, for example products containing the active ingredient metiram. It is important to wet the entire plant and also the underside of the leaves. If you want to use home remedies to prevent this, you can inject horsetail or nettle tea in the critical phases and hope for a preventive effect.
And what about resistant varieties? That's not an easy question 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. It is therefore often not mentioned at all whether a variety shows resistance to rose rust. However, it is always advisable to buy roses with the ADR seal. In general, these rose varieties must be particularly resistant to diseases.
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 that your roses have a good supply of potassium and reduced nitrogen fertilization. With a fertilizer specially tailored to the needs of roses, you can easily achieve an optimal supply. Our Plantura organic rose fertilizer offers a perfect ratio of nitrogen to potassium and ensures strong roses over the long term.
Rose rust control: Effective pesticides
In the case of a light infestation with rose rust, treatment is not absolutely necessary. But if more than a third of the leaves show symptoms, we advise against itreact. We also recommend treatment if you 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 early. Active ingredients against rose rust are, for example, tebuconazole, azoxystrobin or difenoconazole. We recommend that you do not use the same crop protection agent 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 funds according to the application instructions and only in the shortest possible period of time, but until complete control is achieved. If after a certain time you no longer achieve any effect, it is possible that resistant fungi have established themselves. Then you should use a pesticide that comes from a different group of active ingredients. These groups are coded on the packaging of the crop protection products with a capital letter and a number.
A very common pest on roses are aphids. In our special article we will show you how to combat aphids on roses naturally.