A plume moth could be nibbling the leaves of plants as soon as November while the more aggressive horehound clearwing moth breeds only once a year so its release could be a year or so away.
Tekapo farmer and Horehound Biocontrol Group chairman Gavin Loxton said the moths have successfully controlled the weed in Australia and given conditions here are wetter he is quietly confident they will perform better here.
The moths, which still must go through quarantine, provide a two-pronged attack.
The larvae of the plume moth feed on the leaves, weakening the plant, while those of the clearwing moth feed on the roots.
Sheep won’t eat horehound, which is estimated to cost farmers about $7 million a year from contaminated wool. It significantly infests lucerne crops when dormant over winter, reducing the lifespan of the crops.
It is widespread in dry areas of the South Island, Wairarapa, Hawke’s Bay, East Coast, Bay of Plenty and the Chatham Islands.
Since being introduced 20 years ago the moths have reduced Australian infestation to a few unhealthy plants in the corner of a paddock compared to thousands of healthy and thriving plants spread throughout NZ.
“What they consider a huge problem is nothing compared to what we have,” Loxton said.
Such has been the Australians’ success it is logical to use their research, knowledge and ease of access to source the moths.
The moths will have to be distributed manually because they don’t spread far naturally.
Loxton hopes to involve schools to spread them.
Judging by the success of biological controls for ragwort and nodding thistles he wants to see a significant reduction within five years.
The Horehound Biocontrol Group is a collective of farmers who led the application, which was supported by the Primary Industry Ministry’s Sustainable Farming Fund.
EPA hazardous substances and new organisms general manager Dr Fiona Thomson-Carter said 40 submissions on the application were received with 39, including the Department of Conservation and MPI, in favour.
A firm that produces medicinal products using horehound opposed the application because harvesting the weed might become difficult if biocontrol agents are released.
