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Rose black spot

Rose black spot: This fungus causes the characteristic star-shaped spots on roses and laurel.

recognize Rose black spot
Rose black spot on Zépherine Drouin, foto: Rasbak - CC BY-SA 3.0

Rose black spot (Diplocarpon rosae). This fungus causes the characteristic star-shaped spots on roses and laurel. In humid weather, the fungus becomes active. The affected leaves yellow and fall off prematurely.
Spores of the fungus hibernate on the soil; splashing rain infects the lower leaves, after which further infection occurs.
Weak plants are more susceptible to Rose black spot than healthy ones..
Some roses are more susceptible to Rose black spot than others: the thornless climbing rose Zépherine Drouhin is very susceptible, as are older varieties while some cultivars are now resistant.

Where to find

Control

Remove infested leaves. Spraying with horsetail spray.

Prevention

Water around the plant on the ground, do not water the plant itself. This is how you keep the humidity at the plants low.
For susceptible roses, ensure a sunny location so that the foliage does not stay damp for long after a rain shower. After leaf emergence, treat the foliage preventively with horsetail spray.

Pruning waste and prematurely fallen leaves can contain fungal spores; prevent re-contamination and do not put this waste on the compost heap but dispose of it in the organic waste container.

Roses resistant to Rose black spot are also available.