Slime moulds appear as patches of watery or jelly-like slimy material that covers the surface of the soil, pasture, lawns, fallen leaves, or mulch on garden beds. After a few days the jelly-like material produces fruiting bodies that are commonly ash grey, though in some instances they may be bright yellow or red. These fruiting bodies usually occur in great numbers on the affected plant material and may cover an area of up to a square metre.
The organisms survive from one season to the next as microscopic spores that are very resistant to desiccation. These spores germinate under cool, moist conditions and give rise to a jelly-like material that creeps over the soil or surface vegetation. At maturity, the moulds move on to grass, leaves, twigs, etc. and rapidly produce the spore-bearing formations.
The spores are dispersed by wind, rain splash, animals, insects, and other agencies.
Most slime moulds live on organic matter or feed on other micro organisms. The species found on lawns, shrubs and other low-growing plants are not parasitic. However, in some instances they may smother plants or cause them to look unthrifty.
The moulds may also form a water-repellent crust on soil surfaces, which reduces the water available to nearby plants.
In the normal course of events slime moulds will disappear on the return of hot or dry weather. They may also be brushed or hosed away.
Spraying with a copper fungicide solution is a good method of control. However, if you need to spray over lawn areas or close to existing plants or seedlings, one of the milder copper solutions such as copper hydroxide is recommended, to prevent damage to leaves.
It is also worth bearing in mind that poor surface soil drainage can contribute to the problem, particularly on lawn areas, so aerating or spiking the surface to a depth of at least 15cm can help.
Please report any suspect pests, weeds and diseases to the Department of Agriculture and Food, Western Australias's Pest and Disease Information Service (PaDIS) by emailing images to firstname.lastname@example.org or on 9368 3080. You can also make a report using the mypestguide app.