"Every year Horizons spends more than $500,000 controlling the pest by spraying, cutting and supporting community efforts to do the same. To date this has stopped the spread of old man's beard, however we are always looking at what more can be done."
The council has attempted other forms of biocontrol including a sawfly, leaf miner and fungus, but they haven't been very successful. Davey is excited by prospect of using the gall mites, which have been successful with other pest plants.
Importing the gall mite is the culmination of 10 years of hard work organising funding, rigorous testing and going through a thorough EPA application process to ensure the agent only affects the intended host, Davey said.
"Biological control is a technique used worldwide to restore balance between a weed and the environment by recruiting some of its key natural enemies. Pest plants that have been introduced to New Zealand are often not considered a weed in their home country because insects or diseases keep them in check."
The introduced mite will form galls on the host plant, which the plant will redirect resources to, reducing its capacity to flower, produce leaves and photosynthesise.
Extensive testing has been completed as part of the EPA application to ensure the gall mite will not pose a danger to other plant types.
"During the process we were also considering a bark boring beetle that would have been very damaging to old man's beard, however its taste for our native clematis meant this was not a suitable option," Davey said.
The gall mite is expected to be imported into the country in autumn 2019, for release in approximately spring 2019.
"We are planning to make the first introduction of the gall mite to the Taihape area. Many unique and wonderful habitats have been ravaged by old man's beard, and as we have a really engaged community in the Rangitīkei, we'd like to locate these mites in the places too challenging or risky for chemical control."
Horizons applied to the EPA to introduce the gall mite on behalf of the National Biocontrol Collective, comprised of 14 regional councils and the Department of Conservation.
Biocontrol has been undertaken by Horizons in a number of other parts of the region to address pest plants such as field horsetail, broom, wandering willy and ragwort.