Slime molds
Fuligo septica, Physarum & Mucilago spp.
also called Dog vomit fungus, Fuligo
A bright yellow foam on the mulch or a gray powder on the grass. It is not a fungus, it is not a disease, and it is not hurting anything.
- A bright yellow, orange or white foamy mass on bark mulch, appearing overnight after rain and looking exactly as unpleasant as its common name suggests.
- Within two or three days the mass dries to a crusty gray-brown pad that puffs dark spores when poked.
- On lawns, a gray, blue-gray or purple powder coating the grass blades in a patch a hand-span across.
- The grass beneath the coating perfectly green and undamaged when you rub it clean.
- The whole thing gone within a week, and back after the next wet spell.
Not a fungus and not a plant pathogen. A slime mold is a colony of single-celled organisms that creep together across damp organic matter feeding on bacteria and decaying material, then gather into one mass to produce spores — which is the stage you notice. It uses your mulch and your grass blades as a surface to climb, nothing more.
Warm, wet weather over damp organic matter: fresh bark mulch, a compost heap, a lawn with heavy thatch, or shady beds after a run of rainy days. It appears within a day of a downpour and disappears as soon as things dry.
- Nothing needs treating. If it bothers you, break it up with a rake or a jet of water and it will dry out and go.
- Scoop the mass off the mulch and put it in the compost heap, where it will carry on doing what it does.
- Mow the lawn or brush the grass blades to knock the gray coating off.
- Let mulch dry between waterings and turn it over occasionally.
- Do not spray a fungicide. It will not work, because this is not a fungus, and there is nothing to cure.
- Turn and fluff bark mulch occasionally, and keep it to a five-centimeter layer rather than piling it.
- Reduce thatch in a lawn that gets it repeatedly.
- Improve drainage and light in a shady bed that stays permanently damp.
- Water in the morning so surfaces dry through the day.
- Accept it as a sign of a healthy, biologically active mulch — because that is what it is.
Nothing is attacked. It appears on mulch, lawns, compost, low bedding plants and anything else damp that it can climb.
The Cottage Garden Companion — the gardener's apothecary at cottagegardencompanion.com