South Perth, Australia
February 7, 2008
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Redlegged earth mites on a lupin cotyledon.
(photo by David Pfeiffer) |
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Farmers will have to think more
strategically about how to control the destructive pest
Redlegged Earth Mite (RLEM), Halotydeus destructor, now
resistance to insecticide has been confirmed in the south of the
State.
That’s the conclusion to a research paper identifying several
integrated control strategies, to be delivered at the
Department of Agriculture
and Food’s Agribusiness Crop Updates.
RLEM insecticide resistance was first detected in Esperance in
2006. Another incident was recorded near Cranbrook in 2007 with
another suspected at Piesseville.
Mites from Esperance and Cranbrook were tested in conjunction
with the department at the Centre for Environmental Stress and
Adaptation Research (CESAR) at the University of Melbourne. Very
high levels of resistance to two synthetic pyrethroids,
bifenthrin and alpha-cypermethrin, were found.
Senior technical officer Peter Mangano said the resistance
discoveries were a warning to farmers that they may no longer be
able to rely on blanket spraying paddocks to protect their crops
and pastures from RLEM.
“Farmers reliance on spraying has increased in recent years in
association with lower insecticide costs and the increased
adoption of minimum tillage cultivation, which inadvertently
increases the risk of RLEM,” Mr Mangano said.
“However, to ensure the future effectiveness of synthetic
pyrethroids, these insecticides have to be used sparingly and
strategically – just as you would their use for lice treatments
that have the same challenges.”
The research identifies several RLEM control options, including:
correctly identifying RLEM; monitoring; cultural or cultivation
options; insecticide treatments; biological control; and host
plant options.
“There is no point treating for RLEM if it’s not there and it
may just increase the incidence of other mites,” Mr Mangano
said.
“Monitoring RLEM populations to determine control threshold
levels can be difficult but done properly it will minimise
unnecessary spraying.
“Intensive spring grazing of pastures could be an alternative
option to chemical control, as could having fallow periods
before sowing crops and considering the RLEM carry-over risk
following crop rotations”.
The project suggested farmers consider a range of options before
using blanket insecticides, such as to direct smaller quantities
of insecticide to where it was needed rather than over spraying
beneficial predators.
“There are a few biological control agents, however they take
several years to become effective in long term pasture
situations,” Mr Mangano said. The commercial release of more
plant cultivars with reduced susceptibility to RLEM is also a
future possibility.
The discovery of the redlegged earth mite resistance has been
greatly assisted by State collaborative networks established
under the National Invertebrate Pest Initiative (NIPI),
supported through the Grains
Research and Development Corporation (GRDC).
GRDC are a major supporter of Agribusiness Crop Updates.
More information on this year’s event is available from
www.agric.wa.gov.au/cropupdates
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