Various fungal diseases cause brown leaves
If the rose petals develop large, blackish-brown spots, it is often due to the blackened soot - one of the most common rose diseases - caused by the fungus Diplocarpon rosae. If, on the other hand, it is initially orange and only later brownish, the rose rust has attacked your roses.
Treat infected roses properly
Basically, infected areas are to be removed as quickly as possible with the rose shears. After that, the infected leaves and shoots do not belong in the compost, but in the household waste. In severe cases, chemical treatment can also be useful, as otherwise the roses are completely bare of leaves in midsummer.
Prevention is better than cure: Always water roses from below, the leaves must not be wetted or must be able to dry quickly. That's why an airy location is so important! In addition to the appropriate care, the right soil and a sunny, but not too warm place are also relevant for rose health.