Last Word

How to fight the green slime on your drive­way

NZ Lifestyle Block - - Contents - Words Nadene Hall

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

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