Redlegged earth mite resistance becomes more widespread in southern Australia

Further cases of redlegged earth mite resistance have been discovered in South Australia - 200 km from the first site of detection in 2016.

 

Additional cases of insecticide resistance have been detected in redlegged earth mite (Halotydeus destructor, RLEM) populations in South Australia. Several samples were taken from pasture paddocks after RLEM numbers bounced back sooner than usual after treatment. While further tests are required for confirmation, preliminary laboratory tests conducted by cesar and University of Melbourne, suggest that the populations are resistant to synthetic pyrethroids, and are likely resistant to organophosphates.

Insecticide resistance in RLEM was restricted to Western Australia until 2016, when the first case of insecticide resistance in RLEM was detected in south-east Australia. The site of this initial detection in SA is approximately 200 km south-east from the site of the second dectection. At this stage, it is not known if the cases have developed independently or have spread from one place to the other. 

A testing service is being made available across SA, NSW, Victoria and Tasmania. Any grower or adviser experiencing a chemical control failure involving RLEM, or suspecting issues with insecticide resistance, are encouraged to contact us to access this free service. For more information please contact James Maino (cesar) (P: 03 9349 4723; E: jmaino@cesaraustralia.com).

To guide growers and their advisers in their efforts to control RLEM and reduce the risk of resistance occurring, a Resistance Management Strategy (RMS) for South Australia, Tasmania, Victoria and southern New Wales has been developed (in addition to a separate strategy for WA).

The RMS for the Redlegged Earth Mite in Australian Grains and Pastures, developed through the National Insecticide Resistance Management (NIRM) working group and endorsed by CropLife Australia, has been published by the GRDC and is available here.

Is the time right for RLEM control?

Crops and pastures should now be monitored for RLEM, which can build rapidly in spring. In problem paddocks, control can be timed to occur during a short window during spring when mites have ceased laying winter eggs (eggs that must hatch this season), and before they start laying diapause eggs (over-summering eggs that survive until next season). This approach can significantly reduce RLEM numbers the following autumn.

The optimum ‘spring-spray’ dates for RLEM in eastern Australia are mostly between mid-September and mid-October. Exact dates are available through the Timerite^® website 

Some examples of the recommended dates are:

23^th September at HORSHAM

23^th September at ELMORE

29^th September at WAGGA WAGGA

6^th October at FORBES

16^th October at COLAC

 

The date is based on geographical location and is therefore unique to each property. It is recommended that spraying be carried out within the two-week period before the optimal date.

Before using this approach, consideration should be given to the number of mites present and the susceptibility of the crop to be sown next season. Insecticides need to be used judiciously to avoid resistance issues, as recently observed in South Australia.