Brad, a simple power washing will take it right off there. Just be careful not to get the washer tip to close to the wall as it may cut into it.
To prevent it you need to if possible try to get more sunshine on the wall. Extreme shading with large trees that do not allow sun to hit the walls will tend to keep the moisture level on the surface up thus allowing the mold to grow.
I'm with Wood on this one. The best, natural cure is to get more sunshine on that spot. My backyard has a ton of trees and because of all the shade, plenty of rocks have moss on them. In fact, it's so bad, I barely have any grass and instead, have a bunch of moss.
However, a good power washing will clean the surface quite well, just heed Dans warnings.
I use to live in S FL in what had been a part of the Everglades and this was a problem for me. I made a watered down solution of bleach, sprayed on, then used a long handled brush (soft bristles) and scrubbed it down. The bleach worked quickly and little scrubbing. The bleach got down in any grooves and killed the algae or else it would return quickly.
You can throw some house wash solution in with the bleach. The detergent in the wash helps break down dirt and allows the bleach to stay on the house to work longer.
You could also try some safe, Eco friendly products that remove algae like growth from roof shingles such as roof reviver or zymeaway. These are Eco friendly so you dont have to worry about killing anything.
Thanks for all the responses. Changing the shade level to get more sunlight is not an option; the problem is caused by how the house sits relative to the sun path; it's on the north-facing sides that are blocked from sunlight by elevation and other parts of the structure. I *hate* the thought of using a pressure washer on the stucco (fear of damage), so I'll try one of the solutions and the brush options first .
Check out Tim Carters web site Askthebuilder.com. He has a product called Stain Solver. See if that would help you.
you get power washed with a little bleach in the water..
Brad, what type of stucco do you have? Cement, or EIFS with foam boards under the surface? This makes a difference on how you can clean the siding.
Power was and mean green
Power wash it. You might have to use bleach like the power wash says