New biocontrol agent to mine out thistle

Its name might give it away but it’s only hungry for one thing - it’s the Californian thistle stem miner, the latest biological control agent to be released in the region.

Bay of Plenty pest plant officer Walter Stahel said the adult weevils had been released in the Lower Kaimai area in the western Bay of Plenty this week to help control the problematic thistles.

“Californian thistle is an aggressive pest plant that’s well established in the Bay of Plenty,” Mr Stahel said. “Control of the thistle costs our farmers millions of dollars each year in control and lost production through sprays, tractor time and loss of pasture alone.”

Mr Stahel said it was the weevils’ larvae which did most of the damage to the thistle.

“The damage is caused by the larvae mining in the stems and roots which either kills the plants or reduces the plants’ ability to compete with other vegetation,” Mr Stahel explained.

Along with the newly introduced Californian thistle stem miner, the green thistle beetle was also introduced to the Lower Kaimai area this week. The green thistle beetle was successfully released in the Taneatua area in the eastern Bay of Plenty earlier this year.

Mr Stahel said the release of these insects was not a quick fix as its introduction would require ongoing and wider on-farm thistle control.

The Environmental Risk Management Authority (ERMA) has approved the release of the Californian thistle stem miner as a biological control agent in New Zealand after rigorous testing.

Sites where the weevil has been released will be monitored and when sufficient numbers have been established the weevil will be redistributed to other parts of the Bay of Plenty.

Bay of Plenty Regional Council assists Landcare Research with funding for biological control programmes. This weevil joins a group of seven biocontrol agents to be released throughout the region in the past year.

ENDS

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