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Redlegged earth mites coincide with delayed establishment

A slow start for crop establishment increases vulnerability to redlegged earth mite damage.

 

Redlegged earth mite adult (left) and damage (right) (Source: cesar).

 

The redlegged earth mite (RLEM, Halotydeus destructor) is active from autumn to late spring in southern Australia, with hatching of over-summering eggs generally coinciding with early crop establishment in autumn/winter. The slow start to the growing season in many south-eastern regions has increased the vulnerability of young crops to RLEM damage.

Growers should be regularly monitoring crops. Mites are best detected feeding on the leaves in the morning or on overcast days. If mites are not observed on plant material, inspect soil for mites. There are some basic economic thresholds available for RLEM in crops and pastures. These are:

  • Canola: 10 mites per plant at the cotyledon/1st true leaf stage
  • Wheat/barley: 50 mites per 100 cm²
  • Pulses: 50 mites per 100 cm²
  • Establishing annual medic pastures: 20-30 mites per 100 cm²

If spraying is warranted this winter, in addition to using the above thresholds to guide decisions, we encourage growers and advisers to follow a resistance management strategy.

Resistance management strategies are not new to the realm of RLEM management. Western Australian growers and advisers have been dealing with insecticide resistance in RLEM populations for over a decade.

What is relatively new, however, is the discovery of resistance in the GRDC southern cropping region. In response, the National Insecticide Resistance Management (NIRM) working group has updated and merged western and southern cropping region strategies into a national document.

The new strategy has been redeveloped for growers and advisers across Australia and considers alternate management plans based on the presence of organophosphate and synthetic pyrethroid resistance. It also provides a management plan for preventing the development of resistance for areas such as southern NSW and Victoria, which have no known resistance issues in RLEM.

Download a copy of the new strategy here. The strategy will also be available at the GRDC and the IPMGuidelinesforGrains websites.

 

Field observations

Birchip Cropping Group (Wimmera/Mallee VIC)

Michaela Alexander – IK Caldwell (Central VIC)

Chris Dunn – Landmark (Central VIC)

Kim Honey – Elders (Riverina NSW)

Peter Neilson – Grower (Riverina NSW)

Dan Walsh – Murray Valley Rural (North East VIC)

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