Why would I have yellow leaves in some areas and black splotches in others?
Certified GKH Gardening Expert
The yellow leaves could be natural as the rosebush sheds some of her older leaves. Sometimes the lower leaves get cast into the shade of the newer upper foliage, so the rosebush will let them turn yellow and drop off as they are no longer productive to its life cycle. When it gets to be real hot out and we have strings of high 90's to 100+ degree temps, roses will sometimes drop foliage to help allow better air circulation through the bush to keep cooler. The Black Splotches could be either Black Spot fungus or may be Downy Mildew. This fungus will attack the leaves and cause them to turn yellow and can defoliate an entire rosebush if left alone. If you have a significant attack of either fungus going on, I highly recommend buying some Mancozeb fungicide. It is the one product that I have found that will stop both dead in their tracks. It can be purchased on Amazon.com, just search for Mancozeb Flowable Fungicide. You mix it with water in a sprayer and spray it liberally over all the rosebushes foliage. It does leave a yellowish powdery residue upon the foliage as that is how it works. Spray the rosebushes with the fungicide at 7 to 10 day intervals for three sprayings. The black spot marks will not go away on the foliage but if it has been completely killed the new foliage should be free from the black spot markings. The damage that the downy mildew does to the leaves will not go away either but the new foliage should be free from it as well if the fungus was fully killed. If for some reason it was not, do another three time spraying cycle.