Grains Research and Development

Date: 02.03.2015

Research looks for RLEM triggers

Key points

  • Grain growers should maintain vigilance for redlegged earth mite (RLEM) during autumn, as rain patterns change and temperatures cool
  • Make sure you can identify this species and differentiate it from other mites that may require different control strategies
  • In areas where RLEM are present, use the tools available such as TIMERITE® and other cultural control strategies
  • Do not assume a chemical control failure involving RLEM is an application issue – it could be resistance, so seek expert advice 

Models identifying weather conditions that trigger redlegged earth mite egg hatchings in different regions will allow growers to more accurately predict when they need to look out for this pest

Image of Red Legged Earth Mites

In western and south-east Australia RLEM are generally active in the cool, wet part of the year (April to November).

PHOTO: SARDI

Redlegged earth mite (RLEM) – Halotydeus destructor – is a major pest of Australian grain cropping, and increasing resistance to some classes of insecticides is making it even more challenging to control.

To help growers in areas where RLEM is present, Dr Garry McDonald at the University of Melbourne has been developing models that predict the risk of a RLEM outbreak each season, based on the weather patterns. Dr McDonald’s work forms part of the National Invertebrate Pest Initiative (NIPI) and is funded by the GRDC, CSIRO and the University of Melbourne.

Image of Dr Garry McDonald

Rainfall and temperature combine to regulate RLEM egg development and hatching. Dr Garry McDonald has discovered that the triggers in the western region appear different to those in the south-east.

PHOTO: Annabel Clouston

In western and south-eastern Australia, RLEM are generally active in the cool, wet part of the year (April to November). Eggs laid in spring go into a suspended growth state, or diapause, over summer to protect them from drying out.

Identifying the specific weather conditions that trigger egg hatching as the autumn weather cools is crucial to Dr McDonald’s models. Discovering these triggers will allow growers to more accurately predict when to watch out for RLEM in their paddocks.

To discover exactly what these triggers are, Dr McDonald compiled data from various research trials conducted over the past 50 years by state departments, CSIRO and universities. He is now using this data to tease out the climate triggers for egg hatching.

“So far I have quantified how rainfall and then temperature act in concert to regulate egg development and hatch,” Dr McDonald says. “Interestingly, the triggers in the western region appear different to those in the south-eastern region. This supports earlier research findings that suggest there may be undocumented differences between RLEM populations in the western and south-eastern regions.”

Once these triggers are validated across a range of sites, Dr McDonald can determine if they will be useful for growers managing RLEM, and if different management strategies should be developed for the two regions.

Research is aimed at giving growers advanced notice of the risk or severity of an RLEM outbreak. However, to confidently predict outbreak risk, the factors that influence RLEM at the regional and field levels need to be considered.

For this pest, as with others, there are likely to be specific factors that trigger stages in its life cycle, and when these coincide with agronomic practices that encourage their population growth, problems really start to occur.

TIMERITE®

TIMERITE® was developed to help growers time a spray in spring to minimise autumn redlegged earth mite (RLEM) egg production. Following the TIMERITE® guidelines can provide up to 90 per cent control of RLEM but otherwise control can vary considerably. However, TIMERITE® has its limitations and should not be used at the same time in the same paddock for several consecutive years as it may cause the populations of mites to shift the timing of egg production or alter the mite species composition. Rather it should be used with other strategies such as crop rotation and grazing management.

An example of an agronomic practice that favours RLEM outbreaks is a paddock coming out of a weedy pasture and being planted into canola.

More information:

Dr Garry McDonald,  
0419 521 238,
gmcd@unimelb.edu.au

Useful resources

PestFacts SA and western Victoria edition:
www.sardi.sa.gov.au/pestsdiseases/publications/pestfacts

PestFacts south-eastern: www.cesaraustralia.com/sustainable-agriculture/pestfacts-south-eastern/

For a DNA test for insecticide resistance, contact Dr Paul Umina at the University of Melbourne:
03 9349 4723,
pumina@unimelb.edu.au 

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GRDC Project Code GRS154, CES00054, UM00049

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