I'm assuming the correct technique to remove what you suspect is an infected leaf, would be to pinch it off with your fingers at the stem. Would that still include the entire leaf if only 1 of it's leaflets was affected? I have 60 heirlooms of many varieties in the ground and most are having the lower leaves turn yellow with brown edges later appearing. They do not look like any disease I can find but I am still removing and spraying with daconil. I do have aphids though, but I don't think they are the cause.