Horsetail weevil welcomed by Rangitikei pest group
The pending release of the horsetail weevil into Rangitikei is a win for farmers, says a pest group.
The Rangitikei Horsetail Group is using the insect as a biological control agent to rein-in field horsetail.
The group received $174,000 after the planned release date in November was delayed due to an insufficient adult population.
The cash injection, from Sustainable Farming Fund, ensures scientists at Lincoln University can continue to run the incubation programme over the next three years.
Field horsetail, or Equisetum arvense, is an invasive species with green fern-like fronds that grow up to 80 centimetres tall.
Though it dies off in winter, it has a large underground root system that makes it easy to regenerate and difficult to control.
Group member Alistair Robertson said the adult weevil burrowed into the stem of the plant, which made it the most effective control agent.
The insect lays its larvae in the stem, and they eat their way down to the roots and remain there during winter. They then emerge to repeat the cycle.
Horsetail is their only source of food and they have no known predators.
Robertson said the invasive weed posed a threat to sheep, cattle and horses. If a crop is infested by more than 25 per cent, it can be toxic.
The worst affected farms boarded the southern end of the Rangitikei River, and roadsides in Glen Oroua, Kiwitea, Halcombe and Taihape, he said.
The plant’s high silica content wears down teeth and is toxic if cut and dried with grass to make hay.
‘‘It’s principally spread through gravel extraction and laid-down roading material,’’ Robertson said.
‘‘All farms backing onto the Rangitikei River are allowed to take metal from the riverside and put it around gateways and troughs... They have effectively brought it onto their own farm.
‘‘In ideal conditions, by river silts and sands, it can root down to 2 metres. If the plant dies above the surface, it can regenerate. It’s hard to get a chemical that will penetrate that deep.’’
Rangitikei MP Ian Mckelvie appreciated the work of the group to find a solution.
The weed was imported to New Zealand in the 1970s as a herbal remedy from Europe.