Oof. Were it mine, I'd put a bit of cinnamon paste on the leaf spot, and also on the spot where new pbulb will be coming in. Maybe even try to get a little cinnamon back in behind that pbuld leaf if possible. Then I'd put a black sharpie marker outside the margin and see if it spreads beyond it. That's a start.
I had one several years back outside during the summer, and didn't notice there was a gutter drip right where it sat under the eaves. Got a similar looking spot on the same place you have on the pbulb leaf as shown in last picture... only thing I could figure was too much water was dripping down into the crevice and not getting dry. I finally excised a piece of it off with an Exacto knife, being careful to cut slowly so I didn't cut into anything below. It worked to fix it (plus moving out from under the leak in the gutter).
Bacterial Brown Spot in a Psychopsis mendenhall
Linear Mode
