Is this area in alot of shade?
Or underneath a deck or where water comes down?

It is on the west side of the house, exposed to sunlight - no shade - no deck. Just a couple of rose bushes on that side.

I have found that if all the conditions are right, that mildew will grow anywere and anytime. To remove it wash the siding with JOMAX which is a great product.

That is rare in MN where I live,usually moisture has to cause this such as sprinkler systems,no gutters above this area,what #5 said works also Ben Moores deck and siding wash,any kind of deck and siding wash will work.
Make sure you are not getting any bleaching agaent or brightner otherwise your stain will change color.

Hey ret you need to remember that not everyone has stained siding like everyone in MN must have.

Even if it was painted the bleeching agent would still cause color problems.

If you use the Jomax according to directions and if the siding is painted and is not chalky and broken down it will not change the color.