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Unfortunately, the countless species and varieties of the genus Rosa are quite susceptible to various diseases, which are mainly promoted by an unsuitable choice of location or incorrect care. Only wild roses and their hybrids are more robust than many cultivated roses, although these representatives of the rose family are not immune to the most common leaf diseases. These are mainly caused by fungi.
Powdery mildew also affects roses with preference
powdery mildew
Powdery mildew is also known as the "fair weather fungus" due to its increased occurrence, especially on hot and dry summer days. It primarily attacks the leaves and young shoots, and sometimes also buds and flowers. Powdery mildew is caused by the fungus Sphaerotheca pannosa, although there is also a variety that only affects roses. This can be recognized by a white coating on both sides of the leaves and by the reddish-colored leaf ends.
Wrong mildew
In contrast to powdery mildew, downy mildew, which is caused by the fungus Peronospora sparsa, occurs primarily on damp summer days. You can recognize an infestation by the dark violet to reddish-brown leaf spots, which are brown on the underside. The typical white-grey spore coating also appears here at high humidity. In addition to the leaves, the stems are often affected.
blackspot
Also the black spot (caused by Diplocarpon rosae) appears on the leaf mainly in humid weather. The rose petals first lighten or turn yellow, before developing round, black-brown spots. These spots are small at first, but grow larger as the infestation progresses.
rose rust
The fungus Phragmidium mucronatum affects roses mainly in spring and causes the quite common rust disease. This can be recognized quite easily by the large, orange spots on the upper side of the leaves. The rose rust lasts until late summer, when tiny black fruiting bodies form on the underside of the leaves. The fungal spores overwinter in these, only to attack the rose again the following spring.
gray mold rot
Reddish or brown specks on the leaf are typical of an infestation with Botrytis cinerea, the gray mold rot. As the process progresses, soft, putrid spots appear not only on the leaves, but also on the shoots and flowers. Gray mold is particularly common in high humidity and rainy weather.
tips
Most leaf diseases on roses are caused by excessive moisture and especially when the leaves are permanently wet - for example because it has been raining for a long time or due to incorrect watering behavior.