The spores that become Black Spot can exist in "conventional" soils for a very long time, but it that soil is made into a good, healthy soil well endowed with organic matter and with the pH in the range the plants growing there need and a well balanced nutrient base, the Soil Food Web can suppress those spores so that is not a problem for you.

i put compost all over my beds this spring. I saw flowers that did not appear last year, but i still have lots of blackspot on many roses. my roses have been sad this season. I want to make sure i get rid of blackspot for next year if it is in the soil. What more than composting should i have done to the soil to have avoided diesease? I want to do it this fall to be ready for next year.

Thanks Kimmsr. No that bed is not healthy...Way too much hard clay. Been working on getting it in shape. OK. Think I'll pick a better spot for my new baby..Buff Beauty.

Sudzy

Black spot fungus doesn't survive in the soil.

Instead, it survives on infected plant debris -- leaves and canes (stems) that remain in the garden.

Regular cleanup helps reduce the disease. As does a new annual application of mulch to cover any dropped leaves which were missed during cleanup.

Nothing will stop it cold.

Select roses with resistance -- none are 100% -- then provide a full-sun site with good air circulation and provide the necessary care.