Don’t be alarmed if patches of yellow or tan spongy growth appear overnight on your mulch. These are not an indication that your dog is suffering from digestive upset. Fuligo septica is a type of slime mold that commonly appears during warm, humid weather. It thrives in a damp environment, whether from rainfall or irrigation. It is commonly called the “Dog Vomit Fungus” which gives a pretty accurate description of the appearance. It is not really a fungus, but a different group of organisms known as Protistas. Only a science geek would belabor the distinction, so I’ll keep referring to mine as slime molds.
These eyesores can appear on your lawn or shrubs, but they show up most often on mulch. While slime molds look disgusting, they live only on dead plant material so they are not damaging to living things unless they are so large they block sunlight from the host plant and prevent photosynthesis.
Don’t waste time, money or chemicals by spraying with fungicides. The molds will disappear on their own in just a few days. If you want to speed their demise, you can rake through the growths to speed drying of the host material. If you choose, you can remove them and bag them for disposal. Molds are usually yellow for a day or two, then turn tan as they mature and prepare to release reproductive spores into the air.
This slime mold is about six inches across. The tan color indicates that it is nearing the end of its lifecycle. It was lemon yellow yesterday.