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

The Environmental Protection Authority (EPA) 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, and is calling for public submissions. The application is supported by the Ministry for Primary Industries’ sustainable farming fund.

However, 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 could 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.

But it stresses 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.

View application details

What we do: The EPA sets the rules for use of new organisms under the Hazardous Substances and New Organisms Act 1996 by assessing the environmental and economic risks and benefits to New Zealanders and the environment.

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