Tools and resources are available to help manage RLEM in the face of increasing insecticide resistance and lack of alternative chemical options

Tools for managing redlegged earth mites (RLEM) are becoming increasingly important as chemical control challenges grow. Originally introduced from South Africa in the early 1900s, RLEM is now a major pest of winter grain crops and pastures across southern Australia’s Mediterranean-type climate.

Cesar Australia research scientist Dr Aston Arthur says there are a range of effective tools and resources available to support growers in managing RLEM, particularly as insecticide resistance rises and alternative chemical options remain limited.

Resistance

RLEM has developed resistance to both organophosphate (OP) and synthetic pyrethroid (SP) insecticides, with resistance now widespread across WA and parts of eastern Australia. OP resistance is present across WA and in parts of SA and Victoria (Figure 1), while SP resistance has been detected throughout WA and in parts of SA (Figure 2). Dr Arthur says resistance in RLEM is continuing to expand across affected regions.

Figure 1: RLEM response to organophosphates.

Source: Cesar Australia

Figure 2: RLEM response to pyrethroids.

Source: Cesar Australia

“Chemical control options are limited, with only six registered modes of action available – and resistance has already evolved in two of those groups. This further restricts chemical control options, particularly after the crop has been sown, as OPs and SPs are commonly used post-sowing.

“Future management of RLEM must focus on reducing chemical use to minimise selection pressure and lower the risk of more local resistance evolving,” she says.

Timing and tools

With autumn bringing cooler temperatures and wetter conditions, it is the time to start planning for RLEM management, Dr Arthur says. RLEM survive the hot, dry summer months as diapause eggs. When at least five millimetres of rain falls and mean temperatures remain below 19˚C for 10 days, the eggs will start to hatch. This hatching often coincides with the emergence of crop and pasture seedlings.

Dr Arthur says the plant establishment phase is the most critical monitoring period for RLEM, as this is when they cause the most damage. “RLEM management tools support target monitoring and management, optimising spray timing and increasing confidence in managing RLEM risks.”

Tools include the following.

RLEM hatch tool

Cesar Australia – RLEM hatch tool

This tool predicts when RLEM diapause eggs will hatch in autumn. It helps growers assess crop risk and optimise monitoring and management during the critical plant establishment phase when this pest is most damaging.

TIMERITE

Australian Wool Innovation Ltd. (AWI) – TIMERITE

Late winter and early spring is the ideal time to consider TIMERITE. This tool predicts the best spray timing for RLEM to reduce the number of diapause eggs laid ahead of the following season’s autumn hatch. By minimising the production of overwintering diapause eggs, TIMERITE helps lower RLEM hatching numbers and reduce damage in the next autumn. Recent updates to TIMERITE reflect climate shifts and research showing that temperature and moisture influence RLEM diapause timing. These updates also consider long-term residual insecticide use, such as omethoate.

The tool’s accuracy has been improved by incorporating dynamic climate data, and a more user-friendly online calculator has been introduced.

“The updates are expected to significantly enhance its effectiveness, shifting optimal spray dates earlier in the season,” Dr Arthur says.

TIMERITE is most effective when RLEM risk for the next season is high. “This includes situations where RLEM numbers are high in spring in a paddock that will be planted to a susceptible crop such as canola or clover the following season.”

It is also important that the mites are predominantly RLEM. “TIMERITE is not effective against other pasture pests,” she says.

Seasonal Pest Risk tool

AgPest – Seasonal Pest Risk tool

This multi-species tool for canola helps assess and manage risks from RLEM and other resistant arthropod pests. The tool considers agronomic, environmental and management factors, allowing users to explore the impacts of different management options to reduce RLEM risk and improve decision-making.

RLEM Best Management Practice Guide

GRDC – Redlegged earth mite best management practice guide

This guide has recently been updated with the latest advice and best practice recommendations for managing RLEM throughout the season, including strategies for controlling resistant populations.

Grower resistance testing service

With continued investment from GRDC, growers and advisers have access to a free insecticide resistance screening service through Cesar Australia and the Department of Primary Industries and Regional Development (WA DPIRD).

This service helps identify resistance in paddocks, enabling growers to implement effective resistance management strategies.

A simple, rapid in-field test for detecting SP resistance in RLEM in real time directly in the paddock is also available. Instructions are here.

Future research

RLEM research will continue under a new four-year project supported by GRDC investment. Dr Arthur says ongoing research is vital to reducing the impact of RLEM on grain crops. “The new project aims to develop novel management options and enhance existing management tools, ensuring growers receive timely, evidence-based recommendations to effectively manage RLEM.”