Beetle To Make Clean Sweep Of Broom

A beetle with an appetite for destruction has been brought in to battle one of our five worst weeds.

The Canterbury Broom Group, Landcare Research and the NZ Landcare Trust will release the broom leaf beetle in the wild for the first time, on Thursday February 8, near Hanmer in Canterbury. True to its name, the beetle is expected to do significant damage to Scotch broom.

Broom can be found in most parts of New Zealand. Unpalatable to livestock, broom forms impenetrable thickets and shades out desirable pasture species. Although a bad weed now, it could become far worse, as it currently occupies only a small fraction of its potential range. In Manawatu, for example, broom occupies just 20% of its potential range, yet is already a serious problem.

Landcare Research weed researcher Hugh Gourlay says the broom leaf beetle has been kept in containment ahead of the release. He says it is the first of three new agents brought in to attack broom. “We are also rearing a broom shoot moth and a broom gall mite for later release. These two insects are more difficult to rear.

“The broom leaf beetle that we are releasing this week damages broom at all stages of its life cycle, as both caterpillars and adult beetles feed on broom stems and leaves. In its native Europe the beetle has been known to completely strip plants of their foliage.”

A cost-benefit analysis conducted by Landcare Research came out strongly in favour of releasing the beetle because of the serious economic threat broom poses to New Zealand. This study was influential to the Environmental Risk Management Authority’s decision to allow the release of the beetle.

Landcare Research has previously introduced a seed-feeding beetle and a sap-sucking psyllid. The seed-feeding beetle reduces seed production by up to 90%. Psyllids have not generally reached damaging levels to date. A self-introduced twig miner here since the 1950s has reduced growth and killed plants in some areas.

Mr Gourlay says broom will never be eradicated, but the agents should reduce the spread of broom across New Zealand in the long term.

He says the release of the beetle was made possible through the support of the Canterbury Broom Group of concerned farmers and agency representatives, the Ministry of Agriculture and Forestry’s Sustainable Farming Fund, regional councils, the Department of Conservation, the NZ Landcare Trust, and the Forest Health Research Collaborative, who banded together to raise the necessary funds.

Canterbury Broom Group Chairman David Rutherford says people should not expect instant results from the release of the beetles or any other agents.

“This is a long-term project which will benefit our children and grandchildren.”

The broom leaf beetle will be released from 1.30 – 3.30pm on Thursday, 8 February near Culverden. Media are welcome to attend. Please call Hugh Gourlay for exact location and directions.

ENDS