Field horsetail - a weedy fern, is spreading throughout wetter regions of New Zealand, competing with grasses, reducing the productive potential of land and impacting both grazing and cropping farmers.

Landcare Research, supported by the Rangitikei Horsetail Group, has been investigating potential biocontrol solutions to help control it and says a weevil (Grypus equiseti) has come out as the best candidate for the job.

“We are extremely pleased to hear they’ve found a weevil that, if approved, can help tackle the field horsetail issue affecting mainly the Rangitikei region. This will enable land to be returned to more productive use,” said MPI acting director aquaculture, growth and innovation Alice Marfell-Jones.

“Around $300,000 was invested over three years from the Sustainable Farming Fund which has gone towards understanding the effects of the field horsetail and investigating potential biocontrol options.”

Landcare Research researcher Lindsay Smith presented details on the weevil at a Bulls field day late last year.

“Throughout our testing, we found the weevil to be one of the most damaging biocontrol agents causing significant damage to field horsetail,” he says.

“The plant is attacked by both larvae and adult weevils, with the larvae burrowing down the weed’s stems and into its extensive root system.”

Smith says three years of testing the weevil in a biocontainment facility at Lincoln have confirmed it is ‘host specific’ to horsetail and so will only damage horsetail and won’t pose a threat to other NZ flora.

“We will now be submitting an application to the Environmental Protection Authority to seek permission to release the weevil from containment. If we are successful, the weevil will be able to be introduced in to NZ to start work on field horsetail.”

He says the work could not have been done without SFF support. MPI’s Sustainable Farming Fund invests in applied research and extension projects that tackle a shared problem or develop a new opportunity in the primary industries.

Co-funders of the field horsetail research included Landcare Research, National Biocontrol Initiative, Rangitikei Horsetail Group, Horizons Regional Council, Rangitikei District Council, Rangitikei Aggregates and Wanganui District Council.