Australia
November 14, 2008
Aphids have become a serious
problem for canola producers in southern New South Wales and
many growers may not be able to treat them effectively before
crops need to be windrowed.
PestFacts South-Eastern, a service provided by the National
Invertebrate Pest Initiative (NIPI) and supported by growers and
the Australian Government through the
Grains Research and Development
Corporation (GRDC), has reported severe aphid infestations
of canola crops across southern NSW.
PestFacts coordinator Dr Paul Umina said aphids had appeared in
high numbers in the Riverina and the South West Slopes.
“PestFacts receives information on emerging pest issues from a
network of consultants, agronomists and growers and we have
received a series of reports about rapidly climbing aphid
numbers in southern NSW canola crops,” Dr Umina said.
“Some agronomists are telling us it’s one of the highest levels
of infestation they’ve seen in 20 years.”
The three main aphid species which attack canola are cabbage
aphids, which have a dull grey-green body; turnip aphids, which
are olive to greyish green with dark bands on the abdomen; and
green peach aphids, which have an oval-shaped body that may be
pale yellow-green, orange or pink in colour.
Dr Umina said the reason behind the unusually severe aphid
infestation was unclear, although entomologists had speculated
that pre-season rains creating a green bridge in southern NSW
this year, combined with the mild break to the season and warm
spring temperatures, had created very favourable conditions.
“Aphids suck sap from crop plants using specialised mouthparts
and they can reduce yield when numbers are high,” he said. “On
the South West Slopes, parts of some canola crops are completely
covered in aphids from top to bottom and some plants have been
completely destroyed.
“One specialist from the NSW Department of Primary Industries
has estimated that 70% of NSW canola crops will be sprayed to
control aphids this season.”
Dr Umina said spraying at this time could be problematic for
some growers, as many insecticides used to control aphids
require significant withholding periods to be observed before a
crop is windrowed, harvested, grazed or cut for fodder.
“The Australian Pesticides and Veterinary Medicines Authority
(APVMA) has issued an emergency use permit for controlling
aphids in NSW canola crops,” he said. “This allows the use of
dimethoate to control cabbage and green peach aphids and is
valid until March 31 next year.
“It’s important to note that the permit states a withholding
period of 21 days, which applies to the time of windrowing or
direct heading. Growers should ensure they have correctly
identified the species of aphid before considering a treatment.”
Dr Umina said a number of beneficial invertebrates were known
predators of aphids and it was important to assess their numbers
before deciding on a control strategy.
“Reports indicate that beneficial invertebrates have been slow
to build up although there has been a sharp increase in the past
week across many regions,” he said.
There is a range of beneficial invertebrates that attack aphids.
At this time of the year the main species include hoverfly
larvae, ladybird beetles, lacewings and parasitic wasps.
Growers can access detailed information about insect pest
management by visiting
www.grdc.com.au/pestlinks.
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