Why Your Roof Gets Covered with Black and Green Stains and Streaks
Mildew, moss, lichens, and other fungi on your roof benefit from a lack of sunlight and the presence of moisture. Shaded areas under trees and near shrubbery are very susceptible to fungus growth.
Additionally, roofs have asphalt shingles are among the most widely used roofing materials throughout the United States. As the name implies, asphalt shingles consist primarily of asphalt, though the shingles can be organic- or fiberglass-based. Organic asphalt shingles contain once-living materials such as waste paper, cellulose, and wood fiber that the fungi feed on.
The black and green streaks you see on your roof are gloeocapsa magma, a black fungus that migrated up from the gulf states several years back. The green is a mildew (Aspergillus). The roof is the buffet where they come to meet and dine. In the process, it makes your roof unsightly and significantly reduces your roof life, even causing your shingle to bend eventually.