The Environmental Protection Authority has approved use of the leaf-galling mite Aceria vitalbae as a biocontrol agent for old man's beard (Clematis vitalba).

Horizons Regional Council applied to the EPA to introduce the gall mite, which is native to Europe, on behalf of the National Biocontrol Collective, comprising 14 regional councils (including Northland) and the Department of Conservation.

"The Department of Conservation told our decision-making committee that old man's beard is a serious environmental pest for which there are limited control options, especially where it is widespread," EPA general manager of hazardous substances and new organisms, Dr Fiona Thomson-Carter, said.

"Horizons Regional Council submitted that some native plant species, especially in the central North Island, are heavily impacted by old man's beard.

Advertisement

"It noted that in some places this weed has been dispersed by the wind, and has established on cliffs, cloaking vegetation and ultimately killing other plant species."

Horizons was spending more than $500,000 a year trying to eradicate the species, five regional councils around the country estimating their annual spend at around $760,000 in total.

Helicopter spraying of the most suitable broadleaf herbicide cost $1500 per hectare.
"Aceria vitalbae is a gall-forming mite," Dr Thomson-Carter said.

"The galls it forms on host plants provide shelter for the mites, enabling them to multiply.

"The plant redirects resources into the galls, which reduces its capacity to flower, produce leaves, grow longer internode stems and photosynthesise."

While the leaf-galling mite may attack plant species closely related to old man's beard, such as the exotic Clematis stans, Manaaki Whenua Landcare Research told the EPA it was confident there would be no significant damage to non-target plants, such as native clematis species.

Manaaki Whenua Landcare Research, the science provider for the application, noted that the formation of galls would assist in reducing the lateral spread of old man's beard, and as a flow-on effect potentially thin-out canopy coverage and reduce shading of undergrowth.

"Overall, the EPA concluded that native New Zealand plants are not at risk of attack by Aceria vitalbae.

"Spill-over attacks on exotic species within the same clade as old man's beard are very unlikely, as ornamental clematis and old man's beard do not grow in the same areas," Dr Thomson-Carter said.

"The decision-making committee noted the environmental benefit of reducing herbicide usage if biocontrol proved effective. This would lessen collateral damage on non-target plants and reduce the chemical burden on the environment," she added.

According to Northland Regional Council the very little Clematis vitalba found in Northland is controlled by traditional methods. The leaf-galling mite would not be released in the region.