Farmers in Whanganui can get a front row seat tomorrow to see a beetle in the ring against the Californian thistle.

AgResearch and Beef + Lamb NZ are hosting a field day at a farm on No2 Line to show how bio-control agent the green thistle beetle (Cassida rubiginosa) is combating Californian thistle, a plant recently estimated to cost almost $700 million each year in lost productivity.

The beetle was released in 2007 and is now established in several parts of New Zealand, including North Canterbury and Manawatu. Whanganui is the site of the latest release.

In other areas where the beetle occurs, reports of severe and extensive feeding on Californian thistle are encouraging, and suggest great potential for this bio-control agent.


AgResearch is hosting the field day so farmers can see for themselves the effect of the beetle, discuss wider issues of thistle management and learn more about the role of bio-control where one live organism (usually insects or fungi) is used to control another.

Dr Mike Cripps from AgResearch, commenting on the beetle's effectiveness, said: "The damage observed on Californian thistle at our trial site at Lincoln in Canterbury is impressive, and greater than anything I saw while working with this beetle in its native range of Europe."

However, he warned that while initial progress had been impressive, any significant and prolonged effect won't be seen for many years.

"It takes many years for the bio-control agent to become common and be able to achieve damaging levels."

-Tomorrow's field day at Fraser Laird's farm, 861 No 2 Line, Whanganui, is open to everyone. It starts at 1.30pm.