Test your mites for resistance
GroundCover™ Issue: 117 | Author: Alistair Lawson
Growers in the southern grains region are encouraged to use a free redlegged earth mite (RLEM) insecticide-resistance testing service made possible through a national GRDC-funded project led by the University of Melbourne, in collaboration with cesar, the Department of Agriculture and Food, Western Australia (DAFWA), CSIRO and the University of WA.
Resistance to synthetic pyrethroids (SPs) is already confirmed in large populations of RLEM across the WA grainbelt, while some populations in WA also have resistance to organophosphates (OPs). While there are no confirmed cases of resistance in south-east Australia, Dr Paul Umina, from cesar and the University of Melbourne, says it is important growers do not become complacent.
"What has happened in WA could be something growers in eastern Australia face in the near future if we don't use insecticides in a responsible manner," he says. “The recent discovery of OP resistance provides further evidence as to why resistance-management strategies are important for RLEM.
"Another reason for vigilance is the possibility of resistant RLEM individuals moving east from WA. Recent genetic work on RLEM clearly demonstrates there is genetic exchange between these two regions of Australia."
Dr Umina says identification of the gene mutation responsible for pyrethroid resistance has enabled researchers at CSIRO to devise a high-throughput, DNA-based test for SP resistance in RLEM. Mites can also be tested for resistance to OPs using laboratory chemical bioassays.
"By using these services in 2015, there is an opportunity for growers to know what is happening in their paddocks in terms of insecticide resistance."
Current control measures for RLEM are largely based on chemicals, but it is the overuse of those chemicals that is fast-tracking resistance. Dr Umina says one of the challenges the Australian grains industry is facing is heavy reliance on only three registered chemical groups to control RLEM – neonicotinoids as a seed dressing, and SPs and OPs as foliar insecticides.
"That means growers are limited in their options to rotate different chemical classes. To help address this issue, the GRDC is also working with agri-chemical companies to introduce new chemistries to control RLEM," he says.
"There is evidence that some growers in WA got caught out because they were applying cheap insecticides as tank mixes with herbicides prior to sowing,” Dr Umina says. “In many cases this is unnecessary and, from a chemical-sustainability point of view, contributes to the build-up of resistance. When chemicals are needed, we need to rotate across different classes and, wherever possible, think about non-chemical control options."
Non-chemical control options include:
- growing crops that do not support large populations of mites (for example, cereals) before susceptible crops such as canola are planted;
- heavily grazing pasture paddocks through spring in the year prior to sowing crops susceptible to RLEM (for example, canola); and
- decreasing weeds that will host mite populations during the crop phase and around fence lines.
A critical first step when implementing a resistance-management strategy is to correctly identify RLEM. Dr Umina says there are several mites that are easily misidentified in the paddock.
Once RLEM have been correctly identified, the appropriate management can be determined, particularly if the resistance status is known. This may include non-chemical controls, spraying or deciding not to apply an insecticide.
Free RLEM resistance testing
- A resistance testing service is available through a GRDC-funded project led by the University of Melbourne, in collaboration with cesar, the Department of Agriculture and Food, Western Australia (DAFWA), CSIRO and the University of WA.
- In 2015, this service is available to all grain growers across Australia at no cost.
For more information about how to access this testing service contact:
Dr Paul Umina, cesar and the University of Melbourne
03 9349 4723
Svetlana Micic, DAFWA
08 9892 8591
Dr Paul Umina
03 9349 4723
GRDC Project Code UM00049