Beetle agents take over farm

Green thistle beetles released onto a Pohangina Valley farm in 2008 as a way of controlling thistles have successfully spread themselves over the area.

The beetle Cassida rubiginosa originates from Europe and North Africa and was brought to New Zealand in 2006 by Landcare Research as a weapon against Californian thistles, a nasty pest that can cover productive land if not controlled.

Horizons Regional Council environmental management officer Neil Gallagher says the beetles were made available for distribution in 2008 as an attempt to control thistles in the Horizons Region.

“Gay Bakker approached me in early 2008 to discuss weed control options for her 278 acre farm in Pohangina,” says Mr Gallagher.

“After learning about the beetles and coming to grips with the long-term commitment required for bio-control agents to work, Gay received 120 adult beetles. She then placed the beetles in a temporary stock exclusion area with plenty of thistles to allow the beetles to establish themselves.”

Green thistle beetle adults eat holes in the leaves of thistle plants but its their larvae that do the most damage by consuming large amounts of the plants above ground if they are present in sufficient numbers.

“Every year since 2008 I’ve gone back to Gay’s farm to check if the beetles have survived and if they were multiplying,” says Mr Gallagher.

“In 2012 the beetles had multiplied sufficiently for 51 adults to be moved a distance away to another location on the farm. However this year’s inspection revealed the beetles had moved themselves to all four corners of the property which is extremely exciting.

“While it’s still too early to notice any dramatic impact on the thistle population, studies in the United States suggest above ground biomass can be reduced by 88 per cent due to the beetles. What is noticeable at Gay’s farm is the absence of thistles at the original release site.”

Horizons yearly inspections will continue and it’s hoped Gay’s beetle care strategies can be replicated on other farms where the beetles are released. For more information regarding bio-control agents please contact Neil Gallagher on free phone 0508 800 800.

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