Moths to combat weed
Two moths may now be imported into New Zealand to combat invasive horehound, following a decision by the Environmental Protection Authority (EPA).
The Horehound Biocontrol Group, a collective of farmers whose crops are infested with horehound, applied to introduce the horehound plume moth and clearwing moth to attack the weed.They were supported by the Ministry for Primary Industries’ (MPI) sustainable farming fund.
The larvae of the plume moth feed on horehound leaves, while those of the clearwing moth feed on the roots.
The applicant group noted a recent survey estimating horehound costs to New Zealand dryland farmers at almost $7 million per year. The weed is a serious threat to the viability of some farms, as it establishes strongly in hill and highcountry, especially when the valuable crop, lucerne, is dormant in the winter. One farmer noted that horehound quickly grows out of control, resulting in lucerne paddocks failing well before their expected 10-year life cycle.
“The EPA received 40 submissions on this application, 39 of which were in favour,” noted its general manager of Hazardous Substances and New Organisms, Dr Fiona Thomson-Carter. “The Department of Conservation and MPI both supported the application.”
A firm that produces medicinal products using horehound weed told the EPA that harvesting the weed may become difficult if a biocontrol agent was released.
But the committee found that, in unmanaged environments, the moths would be the only means used to control horehound, so herbalists should be able to continue their harvesting by hand. Farmers and herbalists could come to agreements on access and management.
Lucerne is increasingly being used in high country to mitigate the effects of drought. Lucerne flourishes in dry conditions, and provides high-quality feed for longer than traditional pasture grasses. Farmers see it as an ally in their fight against climate change, Fiona said.
“The EPA accepted there are no native species related to horehound that would be at risk if these two moths were introduced. Both were released in Australia 20 years ago, and there was no evidence of adverse effects on non-target species there.”
The EPA said it did not identify any risks to native or taonga species, ecosystems or traditional Ma¯ ori values, practices, health or well-being.
“The committee concluded that introducing the two moths would curb the vigour and abundance of horehound in New Zealand, thus reducing its progressive invasion of new habitats, and sustaining biodiversity.
“The committee noted the potential beneficial effect of reducing the use of herbicides that can kill native or other beneficial plants when used incorrectly.”