Thanks for the suggestions. It's helpful to see the photos (which
finally loaded after I shut down the antivirus/ad blocker: ??). And
the writeup was really interesting too. I've been amazed to see one
orchid I got come back & bloom from near-dead; it was marked down in a
garden center, & then lost all but one leaf, & looked terrible. I've
just rescued a couple more from Walmart, one of which has no roots but
finally after lots of rooting powder, is starting to make one. I'm
amazed how tough they can be.
So, SuE, I put some peroxide on it today. Eek, did it sizzle. There
is a sort of big round cavity where the leaf was; the last stump of it
came out, & the bottom of the hole, which is black, is solid & not
squishy. But the next leaf down has started to yellow in the last
couple of days.
So, how often should I pour peroxide in this hole? This plant usually
gets watered every 4 days. For watering the roots, is it ok to put the
plant in a dish to submerge the bottom part of the pot, or to water
carefully, the roots around the edge of it? And put the peroxide in
the middle at the same time? These roots look good & I don't want them
to dry out, & am scared to put peroxide over them too! (What does
that do to the velamen? Anything?)
I like that the first thing you suggested was peroxide & not something
more toxic. I don't like, and don't have, "toxic chemicals" in the
house as a rule, although somewhere there is a little bottle of
no-damp. Is there a point at which I should consider using it, & if
so, how much? I much prefer the peroxide, pleasepleaseplease make it
work.... !

Alison