Slime mold
A reader recently wrote to ask about the identity of a “foamy yellow substance” that appeared on top of some mulched areas in a shrub border. Slime molds (Fuligo septica) have mystified many a gardener, popping up suddenly and often forming large patches. The fungus-like organism, sometimes called “dog vomit slime mold,” dries to form a yellow or orange crusty material. Slime molds are benign and usually short-lived. They can be raked up or dispersed with a spray of water.