Rose rust: recognise, prevent & control

Here you can learn how to recognise, control and prevent rust on the rose, as well as info on home remedies and sprays for rose rust.

Rose rust (Phragmidium mucronatum or Phragmidium tuberculatum) is one of the most common fungal infections of roses. Infested leaves look unsightly and a heavy infestation can reduce the growth of your roses. We show you how to recognise, combat and prevent an infestation.

Detecting and identifying 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 exhibits pin–sized yellow–orange, and later black spore deposits, it is almost certainly a case of rose rust. In the event of a more severe infestation, something which is thankfully quite rare, premature leaf drop is also possible in the rose. Affected tissue may be enlarged (hypertrophied) as the plant cells swell.

Background information on the harmful fungus

The fungi that because rose rust spread via spores that are transported through the air. Optimal conditions for germination of the fungal spores are prolonged leaf wetness for a period of more than two hours and temperatures of about 20 °C. The fungi overwinter as mycelium in the shoots of the rose or as spores on the autumnen leaves. As it happens, disease outbreaks are somewhat less common than the dreaded rose black spot (Diplocarpon rosae), also called black spot disease. In addition, rose rust is a less harmful rose disease compared to the common rose aphid, and usually causes only cosmetic problems due to the unsightly leaf spots.

Rose rust prevention

Preventing rose rust, as with many other fungal diseases, is a relatively difficult matter. However, if your rose is already infested, there is a trick to ensure that new leaf spots do not appear, or do so only to a limited extent. For this you need to know that the fungus overwinters mainly on old fallen leaves. Therefore, the leaves should be collected and disposed of in the compost, and then well covered with other organic waste. An alternative is to intensively work 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 general waste. The location of the plant also plays an important role. Here it is important to avoid roses that are too close together, and to make sure they are in a sunny position. Also, when watering, we recommend that you keep the leaves dry so as not to provide the fungal spores with the necessary leaf wetting time to germinate. In addition, you should avoid planting wild roses in the immediate vicinity, as they are popular hosts of the fungi. All this makes life more 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 here to wet the entire plant and also the undersides of the leaves. If you want to use home remedies for prevention, you can spray with horsetail or nettle tea during the critical phases and hope for a preventive effect.

And what about resistant varieties? This is a tricky one. Since rose rust is not one of the most important diseases of roses, resistance to it is also not as important as, for example, against powdery mildew. Therefore, it is often not even mentioned whether a variety has resistance to rose rust.

Optimal nutrient supply to your roses ensures that your plant is less susceptible to harmful organisms such as rose rust. Here we recommend you to pay attention to a good potassium supply as well as reduced nitrogen fertilisation of your roses. With a fertiliser specially adapted to the needs of roses, you can easily achieve optimal care. Our Plantura Rose Food offers a perfect ratio of nitrogen to potassium and provides long–lasting food for strong roses.

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Combating rose rust

In the case of a light infestation of rose rust, treatment is not necessarily required. But if more than a third of the leaves show symptoms, we advise taking action. Also, we recommend treatment if you can see an infestation almost every year. In this case, you should pay close attention to infestation from the beginning of May and treat rose rust early. Active ingredients against rose rust include tebuconazole, azoxystrobin or difenoconazole. We recommend that you do not use the same crop protection product every year, but change the group of active ingredients. You can do a switch of this kind for example, with the active ingredients difenoconazole and azoxystrobin. Please use the treatments according to the application instructions and for the shortest time possible while ensuring they are successfully treated. If you do not achieve any effect after a certain time, it may be that resistant fungi have become established. Then you should use a crop 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 of roses are aphids. We will show you in our special article how to fight leaf aphids on roses in a natural way.