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 forPrimary Industries' sustainable farming fund.
However, the horehound weed is highly valued as a medicinal herb, and is harvested for that. A literature review suggests the plant may be beneficial in 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 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 weed are 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 feed on leaves, while the clearwing moth feeds 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, confirmed in Australia before their introduction, it says.
