Q.Black Spot Fungus
I have two rose beds with in 4 feet of each other (similar orientation, airflow, sun, etc.). One has constant trouble with black spot, the other does not. The rose varieties are different and vary in each bed. Still, I have serious black spot problems in just one bed.
Might there be something in the mulch or dirt that is causing the issue in the one bed? I haven’t seen any conversation about that – only how to deal with it once there is a problem.
Certified GKH Gardening Expert
The spores can't survive on bare soil, but will overwinter on plant material. The spores are carried by the wind and splash onto plants when watering. Different rose varieties have different levels of disease resistance, if any, so it more than likely is lack of resistance in the roses in that bed. Plus, you must be diligent to remove infected leaves that drop and also cut back the affected bush. Or the disease continues to the next season.
the soil and overwinter on leaves and stems, waiting for favorable conditions. The spores make contact with the rose by splashing onto it in drops of water.