Black Spot On Roses.
How can I stop the black spot on my roses?
Black spot is a fungal disease, and the best way to stop it, or cut back on the effects it has on flowering is to use cultural methods which are as follows;
Firstly, in the autumn rake up and burn all the old fallen leaves. Secondly, spray the bare stems and the soil under the roses with diluted Jeyes Fluid (make sure you drench the stems, so that the Jeyes Fluid runs into all the cracks in the stems to kill all the over wintering spores).
Thirdly, once you have removed all the old leaves, mulch the soil under the roses with a fresh compost or bark mulch. This stops the overwintering spores in the soil from being splashed back onto the fresh spring growth by rain drops.