New Zealand
February 9, 2009
The pasture pest known as clover
root weevil has spread into Otago. An
AgResearch
entomologist based at the Institute’s Invermay Campus, Colin
Ferguson, a week ago, discovered a low density population on a
sheep farm near Clinton in South Otago. This is the furthest
south it has been found since it was first detected in Waikato
in 1996.
He says although it was just a matter of time for the weevil to
spread further down south, it’s nevertheless disappointing to
see it has finally arrived in Otago. Mr Ferguson says although
the newly discovered population is low density, it is bound to
be more widespread than just one farm with possible larger
populations elsewhere in the area. “The discovery was made on a
sheep farm, but there are many dairy farms in the area and dairy
farms tend to better support CRW populations,” he says.
He says the investigation into this new discovery is still in
early stages and no decision has been made on how to control it.
“There is a possibility of releasing the CRW parasitoid at some
stage, but first we have to identify a suitable population to
act as a carrier.” He says farmers in the area are naturally
concerned but keen to work together on finding ways to control
the pest.
He says it is important to also find out where else in South
Otago the weevil may be present. Farmers in South Otago and even
Southland (Clinton is close to the Southland border) are being
urged to inspect their clover for any signs of weevils. If they
find any weevils or unusual damage to clover leaves, they are
urged to get into contact with Colin Ferguson on
colin.ferguson@agresearch.co.nz. Information to help
identify the weevil and a web page to help report new
infestations is also available at
www.agresearch.co.nz/crw/
Clover root weevil knocked clover production as it spread
through pastures following its discovery in the Waikato in 1996.
By 2005 it has spread throughout the North Island. But, it was
only detected in the South Island in 2006 in Christchurch as
well as near Nelson in Richmond and Rai Valley.
AgResearch entomologist, Dr Pip Gerard, says the impact of the
weevil varies from farm to farm. Good pasture management helps
maintain healthy and productive clover, in particular keeping
pasture well grazed in spring and ensuring sufficient cover in
summer to protect the stolons from sunburn. A pamphlet on clover
root weevil management, which has been compiled with input from
North Island farmers affected by the problem, could be helpful
to farmers in the south, she says. This pamphlet is also
available through Colin Ferguson at Invermay.
A biological control programme was initiated in 1998 and a
parasitoid wasp from Ireland has been released in many areas of
the North Island as well as at Richmond and Rai Valley. This
biocontrol programme has been strongly supported by Dairy NZ,
Meat & Wool NZ, and the Foundation for Research Science &
Technology ever since it began. The CRW parasitoid has readily
established at nearly all of its release sites, including those
around Nelson, and is proving to be helpful in most areas in
keeping the CRW populations under control.
Meanwhile the leader of AgResearch’s Biosecurity Group at
Lincoln, Dr Craig Phillips, says additional CRW have recently
been detected by his group in new locations elsewhere in the
South Island including Takaka, Blenheim and Ashburton. It has
also been found in a variety of new sites around Christchurch.
With a few exceptions, such as at Richmond and Rai Valley, CRW
populations in the South Island have so far only reached low
densities and have not yet caused severe pasture damage, but
entomologists warn that the populations may still be building
up.
Craig Phillips says given the propensity of CRW adults to fly in
warm, dry conditions the current localised and patchy
distributions of the pest are likely to spread at increasing
rates, particularly in Marlborough and Canterbury. |
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