Many gardeners get some leaf spot. It is easily spread. I'd trim back the leaves that are affected - dispose the leaves in bags, not in the compost. Some advise dipping the shears or scissors in rubbing alcohol after each cut. Then you can use a fungicide. Since we're avoiding toxic chemicals that aren't good for the earth, I'm going to try a natural product called Neem oil, which is mixed with water and a bit of detergent for sticking power. Since overhead watering may spread the leaf spot, we're also working up to installing a drip system that avoids the leaves. Our occasional spotting isn't as bad as yours, however. Good luck.
