All my searches here and elsewhere and no answers, yet. My indigo spires (probably) has begun to yellow on many leaves. Each leaf starts off with dark brown spots around the front tip and edges, then goes all yellow and drops off. All info on the web says that Indigo spires has no pest/disease problem, so I'm stumped. I don't see or feel small bugs, no whiteflies or aphids, etc. The plant is in a large pot, in mostly bright shade with two hours of strong, Middle eastern sun, which will get more as the summer sun moves. I have been deadheading the dry flower spikes, and should probably prune it, as it's leggy (I know, it wants more sun, but......) It gets the right amount of water, and is about two years old - one in my garden. The flowers are lovely and I want to save this plant......can anybody guess as to what's wrong? Much obliged.