EPA calls for submissions on weevil to control field horsetail weed

The Environmental Protection Authority (EPA) has opened submissions on an application to introduce the horsetail weevil (Grypus equiseti) as a biological control agent for the weed field horsetail (Equisetum arvense).

The application to introduce this new organism, from the Rangitikei Horsetail Group, is made under the Hazardous Substances and New Organisms (HSNO) Act 1996.

“Biological control agents, like the horsetail weevil, are used as natural enemies to reduce the populations of pests such as insects and weeds. We’re notifying this application to ensure that the EPA can consider all views about potential risks and benefits of introducing this horsetail weevil into New Zealand,” said Applications and Assessment General Manager Sarah Gardner.

Field horsetail is an invasive species and an unwanted organism under the Biosecurity Act 1993. It threatens native plants in sensitive habitats such as wetlands and on the banks of waterways. The aim of this proposed biological control programme is to limit the adverse effects of field horsetail where it occurs, and to reduce the rate and strength of invasion.

The horsetail weevil lays its eggs into the stems of the weed. The larvae feed on the stem, moving down into the plant’s roots and killing the stem. Larger larvae consume and break up the roots, reducing the ability of the plant to produce new fronds in spring. Adult weevils also feed on the stems, often causing the portion of frond above to die.

 The application notes that control of field horsetail using sprays or physical removal is problematic. Small infestations can be eradicated by constant removal of fronds or by repeated herbicide application, but this requires long-term persistent effort and is often unsuccessful as well as uneconomic.

Although its distribution is limited, field horsetail is already too widely spread for all infestations to be found and effectively treated.

It can be found in Whanganui, Rangitikei, Taranaki, parts of Greater Wellington and the west coast of the South Island. Field horsetail has also been recorded on the east coast in Havelock North, Marlborough, Canterbury and Otago.

No native plants or valued exotic plants in New Zealand are closely related to field horsetail. The closest relatives are ferns, but these are only remotely related. The weevil is well established in Europe and has only been recorded on horsetails.

The public are invited to make submissions on the application to the EPA. The submissions period closes at 5pm on March 11.

A public hearing may be held before a decision is made. The EPA will provide at least 10 working days’ notice of the hearing date, time and place. We’ll provide this information to all submitters and the applicant.

View application details and information

Find more information on submissions and the hearing process



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