Black mold patches on wood siding
We purchased an older house that is overall in VERY good shape. However, a sprinkler-placement on the front lawn, plus mold spores in the air, teamed up to turn some areas of the vertical wood siding black. To be more specific, the lower 4-foot portions of about eight boards are stained black. Yet, after a scrupulous inspection, I've determined that all this siding is handsome and sound.
This siding is rough sawn (actually, bandsawed) 11-inch-wide wood boards 7/8" thick - hard to get a replacement for in my area. So because the boards are functionally in good shape and the problem is strictly on the surface, I want to do a cosmetic clean-up.
I remember hearing that household bleach can be used for this purpose. I've also heard that oxalic-acid products can be. (And I remember reading you should never mix these two, since very toxic fumes are yielded.)
I know these chemicals may be used in brand-name products, but the brands may vary with region, so I need to know about what chemicals we're talking about. Are the ones I've mentioned the best products? Anyone know how effective either of them is? Or have another procedure to recommend?
What would be the best thing for me to try on a 'test-patch' area? Thanks.