Is it humid where you live? Its humid here,l where I live. I get that on the beadboard in my carport every year. Power washing removes it all. If its just a few spots, you can do it by hand with the clorox in the spray bottle, or any bottle of spray mildew cleaner. It will come back, if you dont have good air circulation. In my case, its just surface mildew, and looks like yours is too. I run a big fan out there, and it helps it stay away all summer, after its cleaned in the spring. I also have a ceiling fan, but, that alone, wont keep it away, like it does with the big fan running.

Agree with Cat. If you live in a humid climate moving air is the only way to slow it down. You have to stay vigilant and clean it, just another home maintenance item.

Thank you! Great info & tips.

We use 30 Second Outdoor Cleaner on our pontoon boat. There are different solutions you can use as to what you need.

There is something called wet and forget that comes in different formulas too. One is for mold and mildew. Might be an option for you. I have never used it, so have no idea if it is as good as they say it is or not. I do know that Ace Hardware (probably a lot of other places too), sells it. Its probably very much like what Kathyg_in_mi mentioned in the above post.