Rachel Rose: Herbicide resistance rising - let's adapt

RESISTANCE: Spraying herbicide on our crops looks like the law of diminishing returns.

True, we don't have gun control issues like America, but New Zealanders are lamentably trigger-happy when it comes to spraying dangerous chemicals.

I'm not surprised that former Royal gardener Graham Gibbons was so horrified at our liberal use of glyphosate. Laurel Stowell's story for the Wanganui Chronicle hit a nerve last month; for a time it was the most-read story on the entire NZ Herald online network.

Roundup generates strong opinions. On the one hand, greenies loathe it; on the other hand, conventional farms, forestry blocks and market gardens rely heavily on herbicides (of which glyphosate is by far the most popular). So do councils and the NZ Transport Agency.

It's not just weeds in fields and forests far from you that are being targeted, it's suburban roadside edges, highway roadsides, school grounds, parks and public gardens - and very likely your own lawn. Places where your kids walk and your dogs roll.

Graham Gibbons' comments carried particular weight I thought because he works in horticulture and uses glyphosate, very carefully and selectively. That makes him harder to dismiss by glyphosate's cheerleaders.

In fact, it would make sense if the rural sector was leading the call to restrict the use of herbicides. (No, you didn't misread that.)

Why? Let me introduce you to Dr Charles "Merf" Merfield, head of the Biological Husbandary Unit's Future Farming Centre, located at Lincoln University.

Merf told me that the popular herbicides are going to stop working thanks to widespread and incorrect use. He particularly criticises the way they're used in urban areas and on roadsides the length of the country.

"It's not if herbicides fail ... it's when," he warns.

"Globally, there are now almost 500 positively identified herbicide-resistant weeds, 160 of them in North America. Many of them are resistant to multiple herbicide classes, with one species now resistant to 11 different modes of action.

"They are almost completely herbicide-proof, and once you have a weed like that, due to weed seed banks, you have it forever."

In New Zealand, Merf says there are seven or eight weeds whose herbicide resistance has been confirmed through formal trials in greenhouses. More than 30 other cases are suspected.

He says what's going on in New Zealand's cities would get you locked up in Europe.

"It's so incredibly stupid, it's bizarre. It's completely unacceptable to [continually spray herbicides] with regard to biodiversity, soil pollution, protecting water … and [councils] are spending money to do it. In urban areas, weed control is usually for aesthetic reasons. Well, your aesthetic is going to have to change."

And so are the tools we rely on.

Tauranga horticulturist and teacher Kazel Cass has formed a company, Hot Grass, to import electro-thermal weeders out of the UK. The impetus was a caretaker who sprayed glyphosate around the edge of the food forest she helped establish at her children's primary school.

This technology uses electricity to turn the water in plant tissues to steam. It flows through the stem into the roots and delivers a systemic kill that it's impossible for resistance to develop to.

"Everything has a thermal death point. If the plants start getting used to the heat, we'll turn the dial up," Merf quips.

It's also vastly superior technology compared to steam and flame weeders, which are horribly energy-inefficient and less effective because they don't kill plant roots. Or so says Merf, and he should know.

His key speciality is thermal weeding and he's been working in the area for 25 years. "[Electro-thermal weeding] will kill plants outright in one hit.

"In my humble opinion, it's a game-changer".

Before you get carried away (I did), this is not yet a DIY technology. Ubiquetek's Root Wave units need to ride on a trailer or ATV vehicle and can only be used by trained operators in expensive gumboots. They currently use a potentially lethal voltage.

However, research is under way into the backpack-sized unit I so want.

Electro-thermal weeding is in fact old technology. It was successfully proven in commercial applications back in the 1980s only to fall out of favour when new systemic herbicides and weed-wiper applicators arrived.

There's been a leap forward in electronics since then, notes Merf, and he expects the machines will be designed to work at a much higher and (counter-intuitively) safer frequency.

I'm doing my best to make sure Whanganui is included when Kazel takes the Root Wave units on the road to show what they do. I hope our district and regional councils and the contractors they hire will at least check it out.

Kazel is initially leasing the machines to operators she will train in their safe use. She's marketing it as a substitute for spraying parks, streets and schools with herbicides.

Meanwhile, Merf says he has "a bunch of farmers on my back wanting to try this out" and he's focused on building a prototype farm-scale machine.

I hope he's right and electro-thermal weeding is a game-changer, because whether you want to use herbicides or not, you'd better prepare for a future without them.

Our choices and practices now will dictate when that future arrives.

■Rachel Rose is a local writer, editor, gardener and beekeeper. Sources and more reading can be found at www.facebook.com/rachelrose.writer