I have some wood in the garage that's been having this white stuff grow on it. I think its white mold but there's two issues
The wood is stored in a hot, dry, area. Either the garage or outside in the blazing southwestern sun. So as far as i know it's not humid enough for mold.
In the picrel there's also a large white mass formed in a knothole that doesn't look like the rest of the powdery growth.
The wood has been in there for around 2 weeks and I only recently noticed the white stuff so who knows what it is.