What causes green and black streaks on Orlando houses?
Heat, humidity and rain make walls a perfect place for algae and mildew. North-facing walls, areas under live oaks and spots beside sprinkler heads are hit first because they stay damp longest. Stucco is porous, so growth holds on and shows as green, gray or black streaks.
Orange or brown marks low on a wall are often rust from iron in irrigation water. These need a different treatment and may only partly lighten. Dirt, pollen and spider webs build up under eaves, around windows and on soffits too.
- Algae and mildew on shaded walls.
- Rust from sprinkler overspray.
- Dirt and road film on garage doors and trim.
- Mud splash near the base of walls after heavy rain.

