[Cynthia, Prescott, AZ]

My preference would have been to cut the leaf off below the discoloration immediately. Cutting some of the outer bracs won't hurt anything. Use a sterilized cutter for any surgery and dust with sulfur or cinnamon. I like Phyton 27 for serious cases like this, but my experience is that Phyton 27 is on the expensive side for most people. I paid $53 for 8 oz. I hope you got a better deal than this. Definitely hang on to the stuff, and don't waste it on general fungal spotting. If you cut below where I see the damage in the picture, you will not really lose much of the leaf, as there is a lot of growing left to do.

I use the Phyton about once a week or a little longer, what ever is convenient. And since I have a lot of orchids and a lot of work keeping up after them, this dictates how often. I have no hard data on how often to do it. I have a few serious problems right now. They are at least a couple of months past their discovery time, and have now gotten 3 to 4 sprayings. They appear to have stabilized, so they probably wont get any more treatments. However, I spray thoroughly, I don't soak or drench, the material is just too expensive to use it liberally, and spraying seems to work.

As to why this happened, you may want to look at your culture. Weakened plants have these kinds of problems. Maybe not enough light, maybe too cool, or maybe shock from a chemical treatment the plant can't take. Well grown plants (the right conditions) don't get these serious problems, no matter how many spores are around.