Have you heard of Nostoc?

It's scientific name, Nostoc commune, sounds like a chat between Trump and Putin but it’s actually a living organism that troubles more than a few Kiwis on their quarter acre paradise.

Brown-green “gorilla snot” is another name, star jelly, witch’s butter, and mare’s eggs... But most folk call it brown, slimy scum.

It’s a colony of cyanobacteria (blue-green algae) that form dense gelatinous mats of slimy and leathery bits and pieces on driveways, gravel, and bare soil.

It is usually terrestrial but can also be aquatic (such as in wet paddy fields).

The trouble with this stuff is its persistence and difficulty to control. It reproduces by binary fission, meaning each cell simply splits in two when conditions are suitable.

Gardeners often complain that it thrives on Roundup weedkiller, and most other weedkillers for that matter (I doubt that, by the way!!). Chlorine and salt don’t work, and bleach simply runs off the rubbery squishy invader. Copper sulphate and sodium hypochloride are also ineffective.

On the various online “help me” websites (hilarious to read, by the way) people state that some Benzalkonium chloride (a quaternary ammonium compound often used as an algaecide) may be the answer.

Why is it so difficult?

Nostoc occurs anywhere from the tropics to the dry valleys in Antarctica – an impressive range of climatological conditions. In summer it dries out to a crispy, brown material, while in winter it’s lush, soft, and spongy, and blueish green or olive green.

It’s particularly good at coping with water stress. A colleague once did some experiments showing that it could lose more than 70% of its weight in water before cell metabolism was affected – hence its success on driveway shingles.

It grows on alkaline soils in the tropics and doesn’t care about brackish water either. It’s resistant to heat as well as continuous freezing/thawing cycles and it produces no oxygen when it’s dormant. Despite the fact it hasn’t got Chloroplasts, it can fix Nitrogen from the atmosphere.

Nostoc is eaten in Asia, but it’s not recommended (there have been some suggestions of toxicity). Having said that, some varieties (such as Nostoc commune var. sphaeroides) may be beneficial by means of an anti-inflammatory mechanism.

So… how do we control it on our driveways?

Good question! Let us know your success stories…

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