I believe this is black spot, but it was very sudden. What should I do to repair it? I live in Piedmont NC
thanks

It could be a fungal disease but "black spot" is specifically a rose disease. It doesn't look like a rose leaf. Do you know what kind of plant it is?

It looks like a variegated Aucuba. They don't like it too wet.

Yes, it's an Acuba. I love them for 2 reasons: they can grow in shade and I love their look. I dislike them b/c I've killed a couple. Turned black. One went slowly but the other went pretty fast.
@Daisyl - you think it's having wet feet? I had thought it was me.
When my 2nd one was still healthy i tried to give it to a neighbor. He couldn't believe that I was serious and wouldn't take it. Too bad b/c it died later on. Seeing his skill with shrubs, I'm sad that he didn't take it from me, but haven't (yet) said 'told you I'm a killer'.

Sorry. Spelling it wrong. It's Aucuba. Or more specifically it's Aucuba Japonica.
You should definitely remove the leaf with the black spot. It's not going to get better but will just not ever be pretty again. One leaf here and there isn't bad. It's when the whole thing turns black then you know you have an ex-plant.
I think the main problem is too much water. This can cause root rot. And on and on. There are treatments for it but I'd start with cutting back on water. Probably would be good to remove it from the soil it's in. Is your plant in the ground or in a pot?