OMG!!! I see tread marks on your mulch! I'm going to guess that you've brought a little batch of one of the many slime molds home with you from the nursery. I say this because it appears to be crawling over your rubber mulch (as if THAT stuff will do it any good, lol). Slime molds will behave that way. They 'walk'. True fungi does not. Slime molds are not a mold, fungus, mildew, or anything even remotely related to a disease. They feed on organic matter, such as the nursery mix from your azalea (which is probably mostly composted bark fines). It does not need to be removed nor does your plant need to be treated. Slime molds do not affect plants, which you have already observed. I wouldn't worry about removing leaves. Nothing is sick!! Since I see that you are using landscape fabric besides rubber mulch, I doubt very much that you will see this stuff back again. There's nothing that it will want to grow on. Unfortunately, I could not find an image of a slime mold that looks like this but I feel fairly certain that this is what you have. A correction would be most welcome.

Redwood will defently mold up left with no upkeep the mold truns to slime in the rail that will track in off your shoes.Power washing will not kill mold and mildew. J

lindac92, and everyone else... Here's what's being talked about. (Remember, if you're using a "real" computer you can click the photo to enlarge it, then right click the enlarged image and select "View Image", and then sometimes click on that to enlarge it yet again. In this case especially, the larger the better.) I've copied a relatively small portion of the third picture, then magnified it by 200%. That's what you see on the left side of the pic above. On the right side is the very same image, but with the colors far more intensified, not changed, just intensified to a degree that actually makes them easily visible. My guess is that we're looking at mold and/or mildew on the back of the canvas. Without smelling the odor I can't be certain, and others may have a better idea, but here's what seems to be sound advice on "How to Remove Mold From a Painting."

Possibly dry rot--serpula lacrymans? From Wikipedia: Serpula lacrymans has a preference for temperatures of 21 to 22 °C (70 to 72 °F) but can survive any temperature from 3 to 26 °C (37 to 79 °F). It is not clear how much light is needed to promote Serpula lacrymans growth. In terms of aeration Serpula lacrymans often grows near ventilation shafts which shows a preference for concentrated oxygen. A moisture content of 30 to 40 percent is its ideal level in wood to promote fruit body formation.[5] It appears that Serpula lacrymans requires an environment where both inorganic and organic materials are present. The fungus uses calcium and iron ions extracted from plaster, brick, and stone to aid the breakdown of wood,[6] which results in brown rot.