15 Aug 2016

Moth move could curb stinking horehound

9:17 pm on 15 August 2016

A high country sheep farmer wants the government to introduce two types of moth into New Zealand to help control a putrid-smelling lucerne crop weed called horehound.

Sheep in green feed crop looking out over Lake Taupo

Sheep in regular lucerne, which is used as feed (file) Photo: ( RNZ / Alexa Cook )

Horehound looks like mint and is recognised as one of the worst lucerne weeds - sticking to sheep wool and reducing its value, and it can also taint the meat if large amounts are eaten.

Lake Tekapo farmer Gavin Loxton, who formed the Horehound Biocontrol Group, is working with Landcare Research to survey farmers and then apply for government funding to introduce two moths to control it.

"Australia introduced two moths from Europe to control horehound and they've been hugely successful there, and we're just trying to bring those two moths into New Zealand."

He said the weed had exponential growth and needed better controls.

"It's doubling every two years - according to the surveys I've had back. We've got areas [where] we never used to see horehound starting to be invaded."

Mr Loxton believed a few decent droughts over recent years had assisted the weed and, with New Zealand drylands predicted to become even drier, he was concerned the weed would get worse.

"Once pasture has died, horehound can invade and establish quicker than more desirable pasture species.

"This is why the moths were introduced as biocontrol agents in Australia in 1994, because of the increasing prevalence of drought conditions."

The weed had been in New Zealand for over 100 years and herbicides were currently the only control, but Mr Loxton said they were too damaging.

"They leave residual chemicals that stunt the lucerne and significantly reduce yields as much as 30 percent. If it happens to coincide with a dry year you can also lose a lot of lucerne plants.

"They're not actually solving the problem. You're simply left with unproductive land."

Landcare Research researcher Ronny Groenteman also said farmers needed a better method.

"At the moment all farmers can do is use chemical sprays and they only manage, at best, to keep the weed from getting worse. But they're not actually managing to control it.

Dr Groenteman said introducing the moths, one of which fed on the weed's foliage and the other on the roots, should prove be a "relatively straightforward undertaking" given the extensive safety testing carried out in Australia before it was introduced there.

He said the first biocontrol agent could be introduced in as little as two years, with the cost estimated to be around $400,000.

Get the new RNZ app

for ad-free news and current affairs