Two moths may be imported into New Zealand to combat invasive horehound

The Horehound Biocontrol Group, a collective of farmers whose crops are infested with horehound, have applied to the Environmental Protection Authority to introduce the horehound plume moth and horehound clearwing moth to attack the weed. Its application was supported by the Ministry for Primary Industries’ (MPI) Sustainable Farming Fund.

The two moths attack horehound in different ways. 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 a year.

The weed is a serious threat to the viability of some farms, it is said, as it establishes strongly in hill and high-country, 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. MPI noted the negative impact of chemicals on the environment where spraying was used, as against the long-term benefits of bio-control.”

A firm that produces medicinal products using horehound weed told the authority harvesting the weed may become difficult if a biocontrol agent was released.  But the Decision-making 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, which is done by hand.

The committee further noted that farmers and herbalists could come to agreements regarding access to and management of horehound-infested areas to allow harvesting.

“The EPA decision-making committee heard evidence from farmers that lucerne is increasingly being used in the high country to mitigate the effects of drought. They explained that lucerne flourishes in dry conditions, and provides high-quality feed for longer periods than traditional pasture grasses. Farmers see it as an ally in their fight against climate change,” Dr Thomson-Carter said.

“The EPA accepted that 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.”

In coming to the decision to approve the application without controls, the authority noted that it did not identify any risks to native or taonga species, ecosystems or traditional Māori values, practices, health or well-being.

The Decision-making Committee also 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 further noted the potential beneficial effect of reducing the use of herbicides that can kill native or other beneficial plants when used incorrectly, Dr Thomson-Carter said.

All documents relating to the application can be read HERE. 

Source. Environmental Protection Authority 

Two moths would hound the horehound weed but herbalists oppose their importation

Picture of horehound plume moth

Two moths may be imported to combat the horehound weed, which a recent survey estimates is costing New Zealand dryland farmers almost $7 million a year.

The Environmental Protection Authority is considering an application from a collective of affected farmers – the Horehound Biocontrol Group – to introduce the horehound plume moth and horehound clearwing moth to attack this invasive weed.

It is calling for public submissions.

The application is supported by the Ministry for Primary Industries’ sustainable farming fund.

But the horehound weed is highly valued as a medicinal herb, and is harvested for that purpose. A literature review suggests the plant may be beneficial in the treatment of respiratory disorders, diabetes, inflammatory disorders and a wide range of other conditions.

Successful biological control would adversely affect the value of the medicinal harvest.

The applicant notes that the New Zealand Association of Medical Herbalists and the Herb Federation of New Zealand both oppose the proposed biological control programme.

The applicant also emphasises that the horehound weed is a serious threat to the viability of some farms. It establishes strongly in hill and high-country lucerne forage crops and is exceptionally hard to control.

Herbicide treatments aimed at the horehound weed are said to be highly detrimental to lucerne, and may do more harm than good.

The two moths attack horehound weed in different ways, and have been released successfully in Australia. The larvae of the plume moth feed on horehound leaves, while those of the clearwing moth feed in the roots.

The Horehound Biocontrol Group says that experimental evidence suggests neither moth will persist in or damage any native plant or desirable ornamental plant. Both feed on a narrow range of plants in their native Europe, and this was confirmed in Australia prior to their introduction, it says.

Public submissions on this application open on 29 May 2018 and close on ­­­­­11 July 2018.

Find out more about the application and make a submission

Source: Environmental Protection Authority