I wish I could find something to stop it as well. Twice a year I use a bleach solution and straw broom to clean my screen porch. sigh.....I even tried the stuff that says it will "prevent" it but it did not
I use it around the house to kill mold & mildew on stone and siding. I get it at my local Costco. Mix it 5:1 with water in a garden sprayer and spray it on the green areas. Don’t scrub. Let it dry. Give it a few days and the green should disappear. It changes the pH of the area to kill it. Safe for plants.