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Thistle Eating Beetle Highly Rated For Control

16 February 2015

NEW ZEALAND – Graziers could have an insect on their side in the battle against one of New Zealand’s “worst agricultural weeds”.

Green thistle beetles released to assist in California thistle control in 2007 have shown “encouraging signs”, severely and extensively feeding on the plants.

This is according to AgResearch scientists who said noted greater efficacy of the beetle than in Europe because of less competition or more “enemy free space”. Consequently, there is “great potential” for the beetle as a biocontrol agent.

Most likely to benefit are hill country pastures, where conventional controls are costly and impractical.

A statement from the organisation said: "An additional advantage is that it also feeds on Scotch and Nodding thistles."

Dr Mike Cripps of AgResearch 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.”

“In Europe, I recorded approximately 50 per cent mortality one week after a field release of hundreds of green thistle beetle larvae. In contrast, at Lincoln I noted constant densities of larvae for a month on the same shoots.”

Dr Cripps said many years will be needed to see any “significant or prolonged impact” and that the attack weakens rather eliminates weeds, allowing other plants outcompete them.

“Infestations may be reduced to a level that we can live with, or eliminate effectively and economically by other means,” he said. “Biocontrol has the greatest impact when used in conjunction with wider good land management practices. “

TheCattleSite News Desk

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