Update on Big Jim: thankfully the peroxide douse I did when I first discovered this blight seems to have stopped it! I went and bought some Captan, but didn't get a chance to treat the plant with it before I got wrapped up in the regatta. When I finally got to have a day off yesterday, the plant had a few more dead leaves but nothing new showing up, so that is a big relief.
Will keep an eye on it and treat with Captan if the symptoms re-appear, for sure. Maybe it was just the "threat" that did it?
