What is the Fungus on Our Lawn?

Q.We have a fungus spreading on our lawn and would appreciate comments as to how to deal with it. It starts as bright yellow small ‘bubbles’ on the stems and grows quickly to a whitish covering.

The pictures attached show progress. Any help would be appreciated.

(Mr Leslie Oppitz, 8 September 2008)


A.Although what you’ve photographed does look for all the world like a nasty fungus infection, what you have on your lawn actually isn’t a fungus – it’s a slime mould – and the good news is that although it’s a bit unsightly, it’s not harmful either.

Slime Moulds

Slime moulds are fascinating and rather weird things that spend part of their time behaving like fungi and the rest behaving like very simple animals. For years no one really knew how they fitted into the tree of life – with both mycologists (fungus experts) and protozoologists (single-celled animal specialists) each claiming them as one of their own. The puzzle of where they fit into life on earth was ultimately solved by DNA analysis and to cut a long story short, the slime moulds (and there are many different kinds) got a separate special biological group all to themselves – the “Protoctista.”

OK – very interesting, but what about our lawn?

First of all, don’t worry about your garden; your grass isn’t being damaged, slime moulds don’t usually affect other types of plants – although they can occasionally – and they aren’t harmful to the soil. I’m not sure when you took these pictures, but slime moulds tend to be more often seen like this in the spring and then again in early autumn and most usually when there’s been a period of heavy rain. Although where I live has been quite dry this summer, I’m guessing you’re in one of the areas that has been a good bit wetter – which probably triggered this outbreak in your garden.

A Simple Cure

Since slime moulds aren’t a pest as such – they just make the garden look a little ugly for a while – and they do have a minor role to play in helping keep the soil in good condition, generally the best solution is simply to wash them away with a hosepipe.

Although some fungicides are effective against slime moulds, there’s really no need to reach for them. Once you’ve solved the immediate aesthetic problem and washed all the “scrambled egg” off your grass, you might want to think about a spot of prevention.

A Spot of Prevention

You’ll probably already have noticed that once the yellow bubbles have turned whitish as you describe, they will eventually go more greyish – this happens when the slime mould is releasing spores, which will then end up down in the soil. Which means, they’ll be back if you don’t address the conditions that brought them out in the first place.

Obviously you can’t do much to stop it raining, but from those great photographs you sent in it looks as if the patch of affected grass is in a dampish spot, judging by other plant leaves in the picture – so improving the drainage here should help stop it happening again.

Try to rake up any of the dead plant material from the patch and then spike the ground with a rotary lawn aerator if you have one – or a trusty garden fork if you don’t – and then leave everything alone over the winter. Next spring, spread sharp sand over the area and let the worms do their stuff. You’ll soon have better drainage, well aerated soil and the slime moulds should stay where they belong – out of sight!

Fascinating though these strange living organisms are, they’re not exactly pretty!

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