Well, humidity is that of a normal NY summer, same for temperatures, so there's no nighttime chills going on as it's 70 at the coldest. The best guess I hve on the subject is either some sort of fungus that's prevalent in the area or a virus. None of the surounding vegetation seems affected and not all of my plants have the problem, it varies from year to year, sometimes most of them, sometimes only a few. It happens without any stress factors so I'm stumped???? Any other guesses?