Mites ready to take on Southland's broom

BROOM SWEEP: Environment Southland senior biosecurity officer Randall Milne with samples of the biocontrol agent broom gall mite at a field day in Manapouri.
BROOM SWEEP: Environment Southland senior biosecurity officer Randall Milne with samples of the biocontrol agent broom gall mite at a field day in Manapouri.

Efforts to curb broom growth in Southland are one step closer to fruition after the success of a biological control method.

Numbers of broom gall mite, a tiny insect which naturally feed on broom, have built to a level at a site in Manapouri at which scientists feel they can be harvested for other sites.

Environment Southland senior biosecurity officer Randall Milne said it was an exciting development for biocontrol of broom in the south.

"That's the exciting thing about it, it's built up to a level that people can come and take some away and disperse it on their own property."

This was the first site in Southland where numbers of the mite had reached high enough infestation levels that they could be harvested, he said.

Broom gall mites were introduced to Southland in 2009 and are one of the plant's natural predators, Mr Milne said.

The mites damage broom by feeding inside the buds of stems which cause it to produce galls that stunt the development of the plant.

Unlike some other biocontrol agents, which slow the growth rate and flowering of plants, these mites could actually kill the plant in about three years, he said.

Broom was considered quite a serious environmental problem because of its prolific growth rate.

"Once it's established it dominates the landscape," he said.

Biocontrol agents provide an effective way to sustainably manage pest plants as they did not require ongoing management or people out administering them 24/7, he said.

"Long term, it's a lot more sustainable than other methods."

The Southland Times