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Weevil’s release hoped to contain field horsetail weed

Weevil's release hoped to contain field horsetail weed

The horsetail weevil will act as a biocontrol agent in an attempt to control the invasive weed field horsetail, (Equisetum arvense) and its devastating effects on pasture.

Field horsetail is found often extensively in Rangitīkei and parts of Manawatū.

The release is being managed by the Rangitikei Horsetail Group with Horizons Regional Council, NZ Landcare Trust and Landcare Research in Bulls on March 8.

Horizons environmental programme co-ordinator Craig Davey, said biocontrol  agents had been used in the region before, but  this was the first of its type to be used from the pest’s home country, England.

“Biological control is a technique used worldwide to restore balance between a weed and the environment by recruiting some of its key natural enemies,” he said.

Pest plants that have been introduced to New Zealand that are often not considered a weed in their home country because insects or diseases keep them in check.”Davey said the parties had spent years investigating field horsetail, looking for chemical control solutions, considering ways to stop its spread, and biological control.

The weed is like a small pine tree which can be found in most rivers throughout the region including Manawatu, Rangitikei, Oroua and Pohangina and is known to spread to along roadsides through root fragments in gravel used for road-making and builders’ mix. From this point it makes its way through drains, up fence lines and into pasture.

Though it dies off in winter, it has a large underground root system that makes it easy to regenerate and difficult to control.

“We now have the best information about how to deal with field horsetail in pasture and crops and practical steps to prevent establishment by addressing infected soil and gravel movement,” Davey said.

“The horsetail weevil was considered the most suitable option as it attacks plants foliage and root systems. If successful, this project could reduce the spread of field horsetail and reduce its effect on productive land.”

 The Environmental Protection Agency (EPA) approved the release last May.

EPA acting general manager of hazardous substances and new organisms Ray McMillan said no native plants or valued exotic plants in New Zealand were closely related to field horsetail.

“The closest relatives are ferns, but these are only distantly related. The weevil is well established in Europe and has only been recorded on horsetails,”he said.

Federated Farmers said in a submission to the EPA that infestations of field horsetail were much more extensive than reported.

“Farmers and landowners restrict the movement of field horsetail by spraying roadsides and properties and monitoring for the weed pest. However, they are barely containing the spread of the weed pest as spraying merely knocks back the plant and it then regenerates the following season.”

Farmers are hoping the adult weevil, which burrowed into the stem of the plant, would be an effective control agent.

The insect laid its larvae in the stem and they ate their way down to the roots and remained there during winter. They then emerged to repeat the cycle.

Horsetail is their only source of food and they have no known predators.

Clifton Street School from Bulls is holding a field horsetail bug day in recognition of the release and will also be helping to prepare the site and release the weevils.

credit:stuff.co.nz