NZ Landcare Trust launched the Biological Control of Field Horsetail (a community driven project) in July 2013, which aimed to adopt a scientific approach to the control of Field Horsetail. Funding for the three-year initiative came from the Ministry for Primary Industries (MPI) Sustainable Farming Fund (SFF).

Field Horsetail is a perennial fern ally which if eaten in large quantities is poisonous to horses and has a detrimental affect on the condition of cattle and sheep. Horsetail also spoils hay, reducing its value on-farm.

Horsetail grows up to 80cm tall, but dies back in winter. It prefers damp, open ground, particularly along stream and riverbanks, where sandy soils provide perfect conditions for roots to penetrate more than 3 metres deep. While it spreads by rhizomes and small tubers, it is extremely difficult control. From a farmers perspective this makes it a highly undesirable pest plant. Traditional control measures are costly and failed to control or reduce the spread of this weed.

The Lower Rangitikei Horsetail Control Group (LRHCG), whose members come from the local farming community, NZ Landcare Trust and Horizons Regional Council, successfully applied to SFF for $316,150 to investigate and test biological control options. NZ Landcare Trust managed the project, with numerous organisations and landowners providing co-funding. Horizons Regional Council, Landcare Research and AgResearch provided technical Field Horsetail information to assist the project.

Biocontrol offers a cost-effective and enduring solution. SFF project 13/061 resulted in a successful application to the Environmental Protection Authority to release the Horsetail Weevil (Grypus equiseti) as a biocontrol agent for field horsetail. The proposal sought funds to allow weevils to be mass-reared and released throughout infested areas while also involving the community in this process.

Data was collected at release sites to allow future impact of the weevils to be evaluated. Farmers and other land owners/managers (including DOC, Regional Councils, LINZ and Transit NZ) who have areas infested with, or are under threat of invasion by Horsetail, all stand to benefit.

Project Updates


October 2019

A shipment of 50 weevils from the UK was accepted into Manaaki Whenua Landcare Research’s containment facility at Lincoln in June 2019. These weevils and their offspring are now undergoing ‘rephasing’ to sychronise their lifecycle to the Southern Hemisphere seasons.

June 2019

Given our relatively unsuccessful breeding season, the Rangitikei Horsetail Group met in May 2019 to discuss a strategy with how to progress this project. A fresh importation of weevils from the UK was initiated with thanks to Horizons Regional Council for covering the cost of this and an application to extend the project for a year.

Jan 2019

Mass rearing and distribution of horsetail weevil is continuing on through late summer and into autumn of 2019. The volumes of weevil we have managed to release is much smaller, but we are hoping for high survival rates and enhanced quality of the releases as the weevil now being reared in outside conditions at Lincoln.

Clifton Street School, Bulls, has assisted with the development of our first community weevil rearing colony. If successful, we plan to spread the programme to other schools through the Rangitikei and neighbouring regions.

May 2018

The Rangitikei Horsetail Group undertook releases across four sites in the Lower Rangitikei – three private sites and one community site. The proportion of the weevils were retained in the rearing colony. Protracted new adult emergence led to multiple releases of small numbers at some sites as adults became available.

Overall, this has been a successful year for the project, with breeding stock and mass rearing ramping up into Year 2 of this project.

Potential to benefit farmers and landowners nationwide

This funding enabled LRHCG to contract Landcare Research to carry out investigations to identify what bugs will eat or kill horsetail, test they are safe and then hopefully release them onto farms within the Region. Ultimately this project has the potential to benefit farmers and landowners nationwide.