Dear Robin: Nice to hear from you!

This is Black Spot, that caused the surfaces of the leaves surrounded by a yellowish area outside the blackspot, the spots will eventually grow together and cause the leaf to turn yellow, wilt, and fall off. This would cause the plant  unable to function as using sunlight to produce energy for plant to grow and blooms.

Since BlackSpot  can be prevented by regular applications of fungicide spray, just make sure sprayed on both upper and lower surfaces of the leaves and stems; rotate application every two weeks and do it in the morning while the weather is not so hot.

I know you don't like to spray any fungicide as many of us, here are a few suggestions would give you a good start:

1, Variety: Select the good healthy variety

2, Location: plenty of sun, space and airflow

3, Soil: pH 6-7  and well drainage

4, Pruning: early spring cut back to initiate  new grow

5, Sanitation: Keep Clean each early spring clean up all the old leaves or debris

Since you already have roses grown on the ground for many years, then it might be able to  prevent this disease by limiting rose bush exposure to excess water, watering in the morning and only apply to the roots zone not on the leaves, make sure to give enough space between each rose. Air circulation can be improved by pruning and make sure to discard any dead stems or leaves to keep place clean.

In your case if BlackSpot has already effect badly, “Cut Back = Pruning”might be effective remedy. Again clean up area well to void disease reproduces. Please be caution to cut back your rose, it must be cut up to the good healthy eye(bud) and leave good healthy green stems.

Hope this would help!

Ping