Mix cheap white vinegar 3 to 1 with warm water. 3 parts vinegar. Spray on with garden sprayer, wait 5 minutes then high pressure wash. Keep your nozzle 6 inches or less from surface, your siding will look like new.
clorox and water...best siding cleaner ever. One part bleach to 5 parts water. Gets rid of everything. I had white siding on my last house that started turning green in the one shaded area. Sprayed the clorox on with a pump sprayer and hosed off. Clean as a whistle.