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An application to the EPA to permit the release of the first biocontrol agent for field horsetail in New Zealand was approved in May 2016. The larvae of the weevil (Grypus equiseti) hollow out the horsetail stems.

Image – Craig Davey

The decision can be found on EPA's website.


This application will be submitted on behalf of the Lower Rangitikei Horsetail Trust (LRHT), a group supported by the NZ Landcare Trust. This group has funded the development of control agents. Landcare Research is the science provider for this development. Landcare Research has contracted Richard Hill & Associates to prepare the application and to manage the application process on behalf of LRHT, including pre-application consultation with EPA and with Māori and other stakeholders.

Field horsetail (Equisetum arvense) is a perennial weed that comes up each year from a persistent underground root system. This underground mass makes horsetail very difficult to control. Actively growing rhizomes penetrate to greater than 1m in depth, from which green fern-like fronds grow. Attached to the deeper rhizomes are small tubers which remain dormant while the rhizome stays alive. When it dies or is broken up, the tubers initiate growth to produce new plants.

Field horsetail is native to Europe, Asia and North America but is now found in Madagascar, South Africa, South America, Australia and New Zealand. The fossil record shows that this plant has remained unchanged for over 300 million years.

Isolated infestations of field horsetail have been found at Kawhia, Havelock North, New Plymouth and Wellington, but it is widespread in the Manawatu/ Rangitikei – particularly on the floodplains of the lower Rangitikei River. In the past gravel from the riverbed has been used along roads, walking tracks and to building sites, and horsetail has become widely established.

For more information on field horsetail see:

Identification and assessment of risks, costs and benefits

The potential risks, costs and benefits of the proposed introduction to New Zealand of Grypus equiseti and the possible reduction in the abundance and vigour of field horsetail will be identified by literature review and by consultation with stakeholders. When complete, the significant effects identified (highlighted in bold) will be addressed in detail in the application:

It is forbidden to sell, propagate or distribute field horsetail. It has no significant economic or environmental value. Potential benefits of biological control would be the mitigation of the effects described above. The key possible adverse effects of introducing the agents will be addressed fully in the application:

  • the risk of direct damage to valued garden ornamentals
  • the risk of direct damage to native plants
  • indirect effects on flora and fauna as a result of disruption of ecological relationships

Field horsetail belongs to the family Equisetaceae. There are no native species in this family. There are no related species growing in New Zealand that have ornamental or economic value. Host range testing is complete. The host range of the weevil is restricted to horsetails. Native and other valued plant species will not be at risk.

Because these insects will be host specific, population densities capable of interacting significantly with other plants or animals will only be found in close proximity to horsetail, which has a limited distribution. As a result, no significant disturbance of ecological relationships is expected in New Zealand.

Pre-application consultation with Iwi

Applications to introduce control agents against seven weeds will be submitted over the next 18 months. The members of the EPA 's national network Te Herenga will be contacted in August 2014, and invited to enter dialogue on the National Biocontrol Collective's plans to apply to EPA to introduce biological control agents to attack these weeds.

The message to Te Herenga will describe how the applicant intends to assess the risks, costs and benefits associated with the proposed introductions. Members will be invited to identify any issues that they would like to be addressed in the applications. In order of application, the target weeds are privet, Japanese honeysuckle, moth plant, lagarosiphon water weed, old man’s beard, ginger and field horsetail. Three targets (Japanese honeysuckle, moth plant, old man’s beard) have been the subject of previous successful applications, and consultation was completed in each case. The outcome of previous consultations will be presented.

At the request of the applicant, EPA will convene a reference group from Te Herenga to meet and discuss the issues surrounding the proposed applications.

Members of Te Herenga will be informed by EPA when each application is open for public submission, and will be able to comment on how the applicant has addressed issues raised during consultation.

The responses by Te Herenga members specifically related to the proposed introduction of horsetail weevil will be summarised here once it is available:

Pre-application consultation with other organisations

Other organisations consulted were:

  • Fish and Game NZ
  • Regional Councils
  • Federated Farmers
  • Royal Forest and Bird Protection Society of New Zealand
  • Department of Conservation staff
  • QEII National Trust

Summary of responses:

Key documents

Reports on host-range determination

Safety issues are paramount in the minds of biocontrol of weeds researchers. Researchers rigorously test all proposed agents to assess the risk of damage to non-target plants. A set of procedures helps researchers choose a suitable shortlist of test plants, and this methodology is now well-accepted internationally (Wapshere, 1974). The technique is under constant review to update best practice (e.g. Sheppard et al., 2005; Briese, 2005).

The results of host range testing will be fully discussed in the application. Tests are being completed in the Containment Facility located at Landcare Research, Lincoln.

This unpublished report will be peer reviewed and that review will be provided to EPA.The feasibility of biological control of field horsetail in New Zealand was investigated

Cited references

Wapshere AJ (1974) A strategy for evaluating the safety or organisms for biological weed control. Annals of Applied Biology 77: 201–211.

Briese D (2005) Translating host-specificity test results into the real world: The need to harmonize the yin and yang of current testing procedures. Biological Control 35: 208–214.

Sheppard AW, Heard TA, van Klinken RD (2005) Scientific advances in the analysis of direct risks of weed biological control agents to non-target plants. Biological Control 35: 215–226.