Porkpal, that's an interesting observation. I applied the manure for the first time last Fall and had no blackspot in the Spring or throughout the summer. Typically I have it in the Spring and the Fall when the temps drop. I didn't see any this Spring or summer until the Fall (only one time period instead of two). Not only are the temps lower when it appears but it always seems to happen after a hard Fall rainfall. Maybe during the hot summer, the spores are multiplying like crazy. And than when it finally rains in the Fall, the raindrops splash the spores all over the plants and the b/s shows up. Perhaps the key is to spray the roses with a mild solution of baking soda and water (alkaline) early in the morning during the hot summer months to cut down on the spores.
I have already applied the manure this Fall AND will do it again in the Spring. I'll keep you abreast of the results. Thanks for taking the time to write and discuss this matter.
