How to fight the green slime on your driveway
It’s slimy, slippery and most people assume it’s a kind of algae. Confusingly, its common name is ‘blue-green algae’.
But what you’re looking at is a different type of organism, a cyanobacterium of the nostoc family (probably Nostoc commune), and it’s quite a remarkable thing: • it’s a type of bacteria that is about 3.5 billion years old; • it produces its own food using sunlight and carbon dioxide, and releases oxygen; • it has a huge influence on the global balance of atmospheric carbon dioxide and oxygen; • some types of nostoc can fix nitrogen, helping soil microbes; • in some countries it’s eaten (but don’t eat it as the type in NZ is not confirmed as edible).
The problem is it’s very slippery. It’s also not a pleasant thing to look at, having the consistency of jelly and… snot.
When NZ Lifestyle Block was first asked about this ‘slime’ several years ago, we spoke with phycologist Phil Novis of Landcare Research. He has studied nostoc found living on Mt Erebus in Antarctica.
“Nostoc is a remarkable organism, frequently dominating terrestrial habitats in the Antarctic dry valleys, yet also being abundant in some tropical habitats. It is particularly good at coping with water stress. I once did some experiments showing that it could lose 70% of its weight in water before cell metabolism was affected, hence its success on driveway shingle.
“It is one of the most robust organisms on the planet. There are stories of people who had varying specimens dried out for 100 years who then revived it, so it’s pretty tough. People always want to know how to kill it but it’s a losing battle in some ways.”
Phil suggests trying boiling hot water (which destroys the cell walls) or a herbicide. However, he stressed controlling it (not eradicating it) would be an ongoing process. He likened it to fighting gorse, saying it would require repeated applications but you’d never get rid of it completely. That’s because nostoc is easily spread, coming in on vehicles and shoes. Once it’s in an area, it will always be an issue.
The workplaces that have the biggest problem with nostoc are nurseries. Trials in nurseries have found glyphosate products can have an impact, but ingredients in the spray can also encourage it to come back.
Scientists in Oregon studying nostoc infestations in nurseries found two methods that work well: a copper sulphate spray, and solarisation.
The solarisation method uses 6mm clear plastic sheets. Use one with an underside that has an anti-condensation coating for effective solar heating. The sheets need to be weighted down around the edges with a band of gravel to prevent heat leaking out, and to keep the sheet in place. It needs to stay in place for 2-4 weeks to be effective. Don’t let water pool on the plastic as it limits the heating effect.
It is one of the most robust organisms on the planet