Rose black spot: We show how to recognise the black spot disease on roses, how to prevent it and what means you can use to combat the fungus.
Rose black spot can be identified by these symptoms
Rose black spot is a common fungal disease and exclusively affects roses (Rosa). In most cases, the infestation first appears on the leaves near the ground and, in the worst case scenario, spreads from there to the entire plant. The first symptoms may appear as early as May. The disease can be recognised by small, star–shaped spots with a blurred edge. The spots are blackish brown and can reach a size of 3 cm. Later in the course of the disease, the leaves become so weakened that the foliage turns yellow and falls off. If the summer is characterised by many wet and humid weather periods, the rose may lose all its foliage.
Rose black spot pathogen
Rose black spot (sometimes called black spot disease) is caused by a fungus by the name of Diplocarpon rosae. It overwinters in the form of spores in the soil, particularly on old, infested leaves and shoots. But plants can also be infected by the wind. In wet weather with temperatures above 15 °C and high humidity, the fungus spreads particularly quickly.
First of all, old infested leaves and parts of plants must be disposed of with your general waste. The spores do not decompose in the compost and can infest your roses again from there. To prevent fungal spores from gaining a foothold on the rose, it is extremely important to dry the leaves quickly. For this reason, a sunny and airy location is very important. Splashing water should also be avoided when watering, and fertilising with a strong emphasis on nitrogen is also not a good idea. As well as this, many gardeners recommend regular spraying (once a week) with horsetail tea. The silicic acid contained in it strengthens the cell walls of the leaves and the fungus has little opportunity to because an infection.
How to effectively combat rose black spot
Unfortunately, combating rose black spot is often unavoidable. As a result of the disease, flowers are absent or appear only in small numbers, and in addition, the sensitivity to frost of the entire rose is increased. On top of that, the disease is very likely to reappear next year. To put an end to the infestation, we recommend the use of a fungicide. With repeated application, rose black spot does not stand a chance.
Unfortunately, roses are often affected by diseases and pests. So we now show you the most common rose diseases, their symptoms and how you can deal with them.