New Project to Begin
Dense infestation of field horsetail. Image - Horizons Regional Council
An application to develop biological control for field horsetail (Equisetum arvense), put forward by the Lower Rangitikei Horsetail Control Group (LRHCG) to the Ministry for Primary Industries’ Sustainable Farming Fund, has been successful.
The LRHCG represents a diverse group of landowners and managers who have a significant problem with field horsetail, and who have come together to try to find a better solution. Alastair Robertson chairs the group, which also includes other arable and pastoral farmers, and representatives from the aggregate extraction industry, district and regional councils, the New Zealand Landcare Trust, and Landcare Research as the science advisor.
Field horsetail is an ancient plant that goes back to the age of the dinosaurs. This plant reproduces by spores rather than seeds, and is native to Europe, Asia and North America. Field horsetail was first recorded in New Zealand in 1922 and is now a problem weed, particularly where rainfall is moderate to high, and in riparian areas. However, the plant can thrive in many habitats from wet, poorly drained areas of fields and grasslands, and stream edges, to well-drained fields, orchards and crops, and even sandy or gravelly sites like roadsides, rail tracks and beaches. Infestations have been recorded from Kawhia, Havelock North, New Plymouth, Wanganui, Lower Rangitikei, Marlborough, Nelson, the West Coast, Christchurch and Dunedin. The total amount of infested land nationwide is unknown. However, Craig Davey, of Horizons Regional Council, who helped to form the LRHCG, has described the recent rate of field horsetail spread in his area as “phenomenal and unstoppable, with vast potential for further spread”.
Once established, field horsetail can form pure stands that exclude other plants. While grazing animals will often avoid eating the plant, those that do can develop “equitosis”, which can prove fatal in horses. Field horsetail develops extensive underground rhizomes that are resistant to herbicides, making this weed extremely difficult and expensive to control. As well as spreading by wind-blown spores new infestations can also develop from small root or rhizome fragments spread by cultivation or flood. Biological control now appears to be the only cost-effective and sustainable management option for this plant. A feasibility study undertaken in 2008 found that field horsetail was likely to be a good biocontrol target since there are no native or economically important plants in New Zealand closely related to it, and many natural enemies are already well known.
“Now that funding has been confirmed, surveys in Europe will get underway very soon and we hope to collect some promising-sounding natural enemies that we would like to investigate further,” explained Lindsay Smith, who is leading the search for biocontrol agents. These include a flea beetle (Hippuriphila modeeri), weevil (Grypus equiseti), and two sawflies (Dolerus aericeps, D. pratensis). We will keep you posted as this project develops.