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May 22, 2008
PestFax Editor and 2007
Grains Research and Development
Corporation (GRDC) Seed of Light winner, Peter Mangano of
the Department of Agriculture and Food WA (DAFWA), warns growers
that redlegged earth mite (RLEM) populations on two WA
properties at Esperance and Cranbrook have major resistance to
widely used synthetic pyrethroid insecticides.
Toxicology bioassays by the Centre for Environmental Stress and
Adaptation Research at the University of Melbourne showed high
levels of resistance to bifenthrin and alpha-cypermethrin.
A resistance factor of more than 240,000 fold against bifenthrin
and almost 60,000 fold against alpha-cypermethrin, when compared
with susceptible mites, was found in RLEM populations on the
property in the Esperance area.
“This alarming discovery highlights our current dependence on
insecticides and the need for sustainable long term pest
management, using integrated pest management (IPM),” Mr Mangano
said.
He indicated that, fortunately, organophosphates, such as
dimethoate and omethoate, were still effective against the
mites.
Mr Mangano is a member of the GRDC-funded National Invertebrate
Pest Initiative (NIPI), which enables entomologists around
Australia to advance IPM adoption.
RLEM, or Halotydeus destructor, is one of the most
important and widely distributed pests in broadacre farming
systems in southern Australia.
“The mites can be particularly destructive at the establishment
phase of crops and pastures, causing severely reduced plant
density or total seedling mortality, necessitating re-seeding in
some cases,” he said.
“In years with a late break of season, or with late sown crops
and pastures, seedlings may emerge in the presence of large
populations of mites.
“Canola seedlings are particularly at risk, while lupins and
other pulses are more tolerant and cereals and grasses can
tolerate considerable damage,” he said.
DAFWA entomologist, Svetlana Micic says the risk of RLEM
resistance occurring can be reduced by following some simple IPM
guidelines.
“If a RLEM susceptible crop, such as canola, is following
pasture then grazing to two tonnes per hectare of dry weight
will control RLEM as effectively as chemicals,” she said.
Ms Micic indicated that trials have shown that crops following
pasture have higher RLEM numbers than those following a cereal.
“Growers should be aware of varying pest risks following paddock
rotations. Planting susceptible RLEM crops following cereals,
rather than pasture, will reduce the need to control RLEM with
chemicals,” she said.
If insecticides do need to be applied to control RLEM,
insecticide groups should be rotated to minimise the risks of
selecting for resistance to a particular chemical group.
Growers and agronomists who discover mites surviving registered
rates of insecticide are encouraged to contact DAFWA
entomologists, Tel 08 9368 3333, so mites can be tested for
resistance levels.
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