Time to start monitoring canola for diamondback moth
Author: Sharon Watt | Date: 14 Aug 2013
Canola growers in the southern cropping region are advised to now begin monitoring for the damaging diamondback moth (DBM).
Crop pest authorities, supported by the Grains Research and Development Corporation (GRDC), encourage growers to monitor canola for DBM larvae by sweep netting their crops.
DBM activity is already occurring in canola crops on South Australia’s Eyre Peninsula.
Weather conditions over coming weeks will influence rates of DBM population growth, which is generally favoured by relatively warm and dry conditions and suppressed by significant rain events and/or cooler conditions.
DBM larvae, which feed on plant foliage, stems, flower heads and pods, can be responsible for yield losses of up to 80 per cent.
In some regions, the frequency and severity of DBM outbreaks have increased markedly in the past decade, exacerbated by mild, dry winter conditions and the ability of the moth to rapidly develop insecticide resistance.
South Australian Research and Development Institute (SARDI) Principal Entomologist Greg Baker says numbers are likely to increase quickly if DBM infest canola early in the season and if prolonged warm weather occurs allowing the pest to complete three or four generations.
“Crops should be monitored using an insect sweepnet at 7-10 day intervals from now through to windrowing,” Mr Baker said.
A new Diamondback Moth Fact Sheet, published by the GRDC with input from Mr Baker and other entomologists, details how to monitor for infestations, the availability and timing of control measures and the importance of integrated management strategies.
The Fact Sheet states that in early-flowering canola, if more than 10 larvae are found in 10 sweeps then a major outbreak could develop. Crops should continue to be monitored.
During early to mid-flowering and pod formation if average numbers of 50 or more larvae per 10 sweeps are found then spraying should be considered. This threshold increases later in the season.
When crops are at late-flowering and most pods are formed, the average number of DBM larvae needs to exceed 100 larvae per 10 sweeps to warrant spraying.
As canola develops it can tolerate increasing numbers of DBM before significant yield loss results.
Mr Baker said no single treatment completely removed DBM.
“But good spray coverage is critical, because about 20 per cent of DBM larvae are found on the lower part of the canola canopy,” Mr Baker said.
When large outbreaks have occurred, two spray applications five to seven days apart have given significantly greater control of caterpillars and reduced yield loss.
This two-spray strategy ensures that DBM eggs and caterpillars that survive the first application are also controlled. A sweepnet to sample crops three to five days after the first spray will help to determine if a second spray is necessary.
In 2012, two new insecticides were registered for DBM control in canola – Affirm® (Group 6) and Success® Neo (Group 5). A GRDC-funded project contributed data to support the registration of both Affirm® and Success® Neo, and GRDC also supported the provision of a previous timely emergency permit for Affirm®, issued in 2011 by the Australian Pesticides and Veterinary Medicines Authority (APVMA) for conditional use on Lower Eyre Peninsula.
The active ingredient in Affirm® is emamectin benzoate, while spinetoram is the active ingredient in Success® Neo.
Together with the biological insecticide Bacillus thuringiensis, available in a range of products, growers can now choose from three effective insecticide groups.
DBM has developed widespread resistance to many insecticides including synthetic pyrethroids and organophosphates, as a result of over-reliance and poor application of these insecticides across several agricultural industries.
Mr Baker said to reduce the risk of resistance developing to these newer insecticides, growers should spray for DBM only when thresholds are exceeded and alternate between insecticide groups from one season to the next.
He said as part of an integrated management strategy, beneficial insects should be encouraged by choosing selective insecticides that conserve them and only spraying when pest thresholds are exceeded.
“Summer weeds and self-sown canola provide a ‘green bridge’ on which DBM can survive over summer. Controlling these weeds within districts to be sown to canola is another important management control to restrict the potential DBM risk.”
More information on controlling DBM is contained in the new GRDC Fact Sheet which is available for viewing and downloading via www.grdc.com.au/GRDC-FS-DBM. The GRDC pest management resource hub, www.grdc.com.au/pestlinks also provides links to other useful resources.
Caption: Canola growers in the southern cropping region are advised to now begin monitoring for the damaging diamondback moth (DBM). Image Dr Mike Keller, University of Adelaide.
Greg Baker, SARDI
08 8303 9544
Sharon Watt, Porter Novelli
GRDC Project Code DAS00094