While we're concentrating on a predator-free New Zealand, rampant weeds are choking the life out of our native species - and we can't keep using chemicals on them.
Photo: RNZ/Carol Stiles
The search for a way to deal with New Zealand's $1.7 billion weed problem - without relying on herbicides - has thrown up a solution straight out of the future.
If the AgResearch invention can be developed commercially, expect to see drones cruising paddocks and vineyards to swoop on weeds, blasting them with a laser bolt of intense heat to kill them instantly.
You can watch a video of it here:
AgResearch principal scientist Dr Graeme Bourdôt was involved in the 'Map and Zap' programme.
"It certainly is a novel way of killing weeds," he says.
"The idea is that you map a species from the air with a camera mounted on a drone... that same drone may also be carrying a laser which can fire a shot at the weed and kill it.
"I think the idea has potential in certain areas of weed management, particularly perhaps in natural environments where you've got very difficult-to-access sites, say down bluffs where currently we have people abseiling down to dig out some plants.
"I can imagine Map and Zap being potentially a much safer replacement for that method of weed control."
Whether it becomes mainstream for managing weeds in crops or pasture remains to be seen.
"In those cases we are talking about hundreds, if not thousands of weed plants per square metre," says Bourdôt.
Today on The Detail we look at why these unwanted plants pose such a danger to the economy, why we have to cease our national love affair with herbicides, and what other methods we could use to rid ourselves of weeds.
For example, Stu Loe is a farmer from the Scargill Valley in North Canterbury who is trialling the use of a leaf-eating tortoise beetle which kills Californian thistle.
It's been about 10 years since their introduction.
"We've still got them and they're chipping away," he says. "It's not going to happen overnight, but I am seeing reduced numbers where we've released them."
Loe hasn't used herbicides for thistles for about 15-20 years, saying the spray drift could damage the crops at nearby vineyards.
He's confident that the beetles won't spread beyond the thistle, because that's all they eat.
Weeds reduce biodiversity, outcompete native plants and kill whole species. In agriculture they reduce the yields, quality and sometimes the marketability of crops, or introduce extra costs in processing.
"A weed, in my definition, is simply a plant that impacts negatively on some human endeavour," says Bourdôt.
In cases such as Chilean Needle Grass, which is becoming a problem, they can have a devastating effect.
"It's got these very sharp drilling seeds that drill straight through the fleeces, through the skin and into the underlying muscles of animals.
"The pelts become useless because they're full of holes, the muscles have got abscesses so the meat is downgraded, the animal has health issues during its life because it might be blinded by the seeds."
There are only about 2300 native plants in this country - but there are between 22,000 and 25,000 introduced exotics. Every year about 20 species, known as 'sleeper weeds' become a problem.
When conditions are right, they "jump the fence" from suburban yards. Such conditions could be something like two mild winters, and with climate change that's becoming increasingly worrying.
Dr Margaret Stanley, an ecologist at the School of Biological sciences at the University of Auckland, says New Zealand spends very little on weed control - "which is really why it's out of control".
She says weed eradication is the poor cousin of Predator Free 2050.
"People are really hyper-aware of possums and rats and things that you can see cause immediate death to birds. But often we have this, what we call 'plant blindness' where you just see green. You don't actually know it's a weed and you can't see the immediate death of a bird, but in actual fact that weed is removing all the resources for the birds and completely smothering the habitat.
"I think it's really hard for people to understand the impact of weeds because it's really slow compared to... a stoat or a possum or a rat."
Anything that's been planted in a widespread way - such as kiwifruit or wilding pine - is highly likely to become a weed.
"Traits like, you can just break off a fragment and it will grow from a fragment - that means it's more likely to spread around. Bird-dispersed seeds is another one... and is it really tolerant of a lot of soil types? There are a lot of different reasons why sleeper weeds start popping up. Sometimes it's just because it takes a long time. Trees... we can have them for 100 years in the country before they start becoming weeds."
Stanley is urging people who go to the garden centre to think about what they're buying - and nursery owners to think about what they're selling.
She says the next big challenge for nurseries is to invest some time into figuring out a good group of trees, shrubs, grasses, and native herbs that would grow well in people's gardens and that could be grown in commercial numbers for back yards.
And she wants a word about tidiness.
"I think a lot of herbicides are used actually for lawns and berms - tidiness - which I don't think is a great idea.
"I think we should live with a little bit of messiness."
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