We have recently received an enquiry asking for identification of a strange fungus like growth on tomatoes. The growth appeared almost overnight and there was concern about what it would do to the tomato plants and fruit.
The growth (seen above) is a slime mould called the dog vomit fungus or scrambled egg slime (Fuligo septica).
Slime moulds are an informal group of organisms that can live freely as single cells or gather together to form multi-cellular structures. Although they may look like fungi they are classed as protists.
They feed on microorganisms that live in or on dead plant material. Although they spend most of their time as single cells, when food is in short supply they can congregate and start moving as a single body. In the multi-celled state they can detect food sources and can change the shape and function of parts of the mass. They may form stalks that produce fruiting bodies, releasing spores, light enough to be carried on the wind or hitch a ride on passing animals.
The above dog vomit fungus slime mould disappeared again over a couple of days and did not cause harm to the tomatoes.