How to prevent blackspot on roses using Jeyes Fluid?

My roses are susceptible to blackspot. I heard that applying Jeyes Fluid into the soil can prevent this issue. Is it true, and if yes, when and how should I do it?

While it used to be recommended, Jeyes Fluid is not a suitable option to use on soil anymore, and it would have limited effect on black spot. The best way to prevent blackspot on roses is to spray a rose fungicide such as Rose Clear from bud break.