My bag of mulch has white specks in it that looks like powder. I don't
recall seeing it on there last year. Could it be some sort of fungus?

I bought it and opened it last year. I stored the mulch in it's
original bag and then placed that bag in a trash bag and tied it up.
I've kept the bag in my spare room since I got it last year.

If the mulch has a fungus, wouldn't it be bad to use on plants such as
tomatoes and peppers? I'm growing tomatoes and peppers in large pots
and was going to use this mulch in the pots. I'm worried about the
fungus infecting these plants.