Signs of success for weed weevil
Success seems likely in the fight against field horsetail weed, prompting a Rangit¯ıkei group which has been focusing on the pest to hold a celebratory workshop at Ferry View farm.
The Northern Hemisphere weed spread to the coastal Rangit¯ıkei farm with 2004 floodwaters and became firmly established, Horizons environmental coordinator Craig Davey said.
Field horsetail (equisetum) reproduces by spores and establishes huge root systems. It can out-compete grass and spoil hay. It survives in a range of soils, especially likes open and floodprone areas and is almost impossible to eliminate.
It is widespread in other parts of the region, including the sides of the Waito¯ tara and upper Whanganui rivers, and it has spread to district roads with river gravel.
Efforts were made to kill it, but by 2007 it seemed it could not be eliminated and would have to be lived with, Davey said.
The Rangit¯ıkei Horsetail Group formed in 2012, chaired by Ferry View Farm manager Alistair Robertson. The group got government funding and tried a lot of different spray methods. Biocontrol was the next option and the group engaged Landcare Research scientists who organised the introduction of a weevil to New Zealand.
The weevil was about 1cm long and looked like a tiny armoured elephant, Davey said. It ate the leaves of the plant and laid eggs on the stem. When those hatched, the larvae ate the stem and the adults moved down into the roots, weakening the plant.
When it became certain that introducing the weevil would have no harmful effects, the Environmental Protection Authority approved its release.
The weevils were bred in a lab, and more than 500 were released at six places in 2017-19. One of those places was Ferry View Farm, and it has shown the first evidence that the weevils have established and are making a difference. “There’s nothing to write home about, but the plants are looking beaten up,” Davey said.