Red legged earth mite (RLEM) insecticide resistance continues to challenge Western Australian landholders, prompting a greater focus on integrated pest management to optimise crop yields.
The Department of Primary Industries and Regional Development examined the effectiveness of several different insecticides to control the pest in laboratory trials in a collaborative project with Grains Research and Development Corporation (GRDC) co-investment.
The results were discussed at the 2020 GRDC Grains Research Updates in Perth recently.
RLEM collected from 73 sites in medium to high rainfall areas of the WA grainbelt were exposed to organophosphate (Group 1B) and synthetic pyrethroid (Group 2A) insecticides.
Department entomology research scientist, Svetlana Micic, said laboratory trials confirmed none of the chemical groups could be relied upon to effectively control RLEM.
“Over half of the sites had RLEM survive recommended insecticide rates,” Ms Micic said.
“Of concern is that about 30 per cent of sites had RLEM that survived exposure to synthetic pyrethroids, as well as to more than one insecticide in the organophosphate group.
“These results show that organophosphate and synthetic pyrethroids insecticides cannot be used to effectively control RLEM long term.”
Reports of RLEM causing early season crop damage – especially in canola – were particularly prevalent in WA last year, most likely due to the staggered germination of canola at the start of the season.
The prevalence was probably due to peak hatchings of RLEM coinciding with paddocks that had both germinating seedlings and established plants.
In these paddocks post-sowing pre-emergent insecticides had little effect on the hatched RLEM.
Ms Micic said the insecticide research highlighted the need for landholders not to solely rely on insecticides to control RLEM and to employ a range of strategies to reduce the pest’s impact on crop yields.
“Crop rotations are an effective way to reduce the risk of RLEM by sowing high risk crops, like canola, after low risk crops, such as cereals,” she said.
“It is also important to stay on top of the ‘green bridge’ and remove summer weeds that could provide a habitat that harbours RLEM into the growing season.
“Growers could also consider using insecticidal seed dressings and grazing pasture paddocks heavily late winter, particularly prior to sowing susceptible crops.”
Insecticide treatments to control other pests that could also impact on RLEM also need to be considered as part of an integrated pest management strategy.
“Every time a broad spectrum insecticide is used to control pests, such as aphids, RLEM also receive a dose of this treatment – despite not necessarily being the target – which can elevate resistance,” Ms Micic said.
“Alternative insecticides should be considered for use in canola, other than those from the synthetic pyrethroids and organophosphate groups, such as Diafenthiuron (Group 12A).”
The RLEM resistance testing was conducted as part of a GRDC research project led by the University of Melbourne, in collaboration with cesar (Centre for Environmental Stress and Adaptation Research) and the CSIRO.
More information on RLEM treatment and control options is contained in the Resistance Management Strategy for RLEM on the GRDC website.
The 2020 GRDC Regional Updates are scheduled for coming weeks. For details and to register visit the GRDC Updates and Events webpage.
Jodie Thomson/Megan Broad, media liaison
+61 (0)8 9368 3937