Slime moulds do not attack plants, but obtain their food by engulfing bacteria, fungal spores and other tiny pieces of organic material as they move. Some slime moulds spend most of their life as single-celled, amoeba-like structures, invisible to the naked eye. Others form a larger structure called a plasmodium. The plasmodium constantly changes its shape as it creeps along, and is sometimes seen as a white or yellow (but sometimes other colours) slimy ‘sheet’, or a network of strands, on the soil, grass or stems and lower branches of plants.
Slime moulds are triggered into spore production by environmental conditions. Depletion of nutrients is a common trigger. The spore-producing structures may develop throughout the year, but are found most commonly in late summer and autumn. The spores of many slime moulds are extremely resilient and can survive for many years before germinating.