The spotting on your house is the spores shooting through the air from the natural decaying process in the mulch. Act early on the first week to power wash the stain spots or they will be mush harder to remove. 

The artillery fungus, or shotgun fungus, is a wood-decay fungus that likes to live on moist landscape mulch. The worst thing about this fungus is that it shoots spores up to 20 feet, which often land on siding, cars and anything else that surrounds the mulch.

The only way to ensure that artillery fungus never comes back is to take out the mulch completely and replace it with stone, artificial mulch or ground-cover plants. However, if you dislike stone and still want to replace the fungus infested mulch with organic mulch, the best way to keep the fungus away is to use a course ground of wood chips. The larger pieces of wood will stay mostly dry and the artillery fungus won’t like it as much as moist, finely ground mulch. Generally, the key to preventing the artillery spores from ever sprouting is refreshing your mulch regularly.

NYBG Plant Information Service