The easiest way is to get some Jomax, which you mix with a little bit of bleach and then spray that on with a garden or bug sprayer. Let that sit for a few minutes and then power wash it off. Heavily mildewed areas may need to be treated twice. Sometimes a scrub brush helps, but power washinng is usually enough.

I do pretty much what paintguy said. (We have a cedar fence stained in semi-solid that gets mold under the shaded horizontal supports, and a solid white stained picket that will get some green>black mildew/mold on the shady side). Sometimes bleach water is enough, sometimes I combine Soilax + bleach (it's no longer available so am using last of my stash, will have to look into Jomax).

Don't get too close to the wood with the pressure washer, you can send splinters of wood flying off. I twist the nozzle for fan spray rather than jet stream also.

Our white fence will need done this year and I have a can of Cabot's solid white stain on hand. Have never used their solid but was really pleased with the Cabot semi cedar tone on the privacy fence. The original white I used was an Olympic stain I got from an independent paint store (not big box). It held up pretty well for 14 years, no yellowing or anything. Exterior solid stains have probably made a lot of progress since then, tho, so there could be some better choices out there.

I can tell you in recent years I used Behr stain on rental decks, complete waste of time and $ for me. That stuff was fading/pulling off by end of summer (I applied in spring). Not just in walk paths, either, but surfaces hit most by sun, or railing where hands occasionally rubbed. Did all the proper prep, too. Google and you'll see complaints on their stain (I checked too late, after the fact when I noticed the problems.) On our old deck I had good success with REZ solid stain, but primed with their oil-based primer first, then stained (per paint store instructions).

Thanks for the suggestions! I do have rosebushes and other plantings along some of the fence line. How could I protect them?

Soak all your plants with water first before spraying any kind of solution with bleach in it. If the bushes are in actual danger of being power washed, then I would use a big piece of cardboard as a shield.

Okay, that's a great idea to soak the plants with water first. Paintguy, can you recommend one white stain over another? Per Moonshadow, I wouldn't purchase the Behr.

TIA for all the help

If you are talking about acrylic stains then I like C2, Coronado Maxim 2 or Benjamin Moore Super Spec in that order.