New Zealand EPA seeks submissions on weevil to control field horsetail weed

The New Zealand Environmental Protection Authority (EPA) opens 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.  

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. Field horsetail 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.

There are no native plants or valued exotic plants in New Zealand that 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.