Future options for the control of Redlegged earth mite in Australian grain crops

Background

Pest mites are a significant threat to the establishment of grain crops. Some species have become more problematic over the last decade as farming practices have changed, while others are proving difficult to control due to tolerance and insecticide resistance issues. The emergence of resistance to synthetic pyrethroids and organophosphates in the Redlegged earth mite (RLEM; Halotydeus destructor) is of particular concern to the Australian grains industry and demands a rethink of management approaches.

Insecticide resistance in the RLEM was first detected in 2006 in WA. High levels of resistance to pyrethroid (Group 3A) insecticides was detected, demonstrating that this resistance has a genetic basis. Since 2006, resistance in RLEM has been found at >50 properties in WA, with these properties spread across >1000 km. A novel mutation in the para-sodium channel gene is responsible for this high level of resistance. The mutation was identified through genomic analyses and is now being used in rapid screening of resistance frequencies and field diagnostics.

Until 2014, resistance was confined to pyrethroids, however field resistance to organophosphates (1B) has since been discovered in several WA properties. With long distance mite dispersal, resistance is likely to become widespread across WA and potentially expand to other regions of Australia. Importantly, insecticide resistance in RLEM has translated to economic losses in the field due to ineffectiveness of chemical applications and mortality of crop plants at seedling establishment caused by surviving mites.

A key component of the current investment (ends June 2020) has been the optimisation of insecticide-testing methodologies and the integration of field diagnostics which have been made available to growers. Broad-scale field surveillance and fitness studies are vital to feed into Resistance Management Strategies that include recommendations such as rotations of chemical classes, timing of pesticide application(s), controlling weed hosts and the use of insecticide seed treatments in order to minimise resistance development through the over reliance and ad hoc applications of insecticides.

This investment will build upon previous work to improve long-term management and monitoring guidelines for implementation across the areas affected by this pest.

Investment Description

The occurrence of insecticide resistance in the redlegged earth mite (RLEM; Halotydeus destructor) is of particular concern to the profitability of the Australian grains industry, and demands a rethink of management approaches. This investment will provide contemporary recommendations about insecticide resistance management and improved control methods for this pest. This will be achieved by:

• Maintaining active surveillance to understand the RLEM insecticide resistance status across the grain growing regions affected by this pest
• Ensuring that the RLEM Resistance Management Strategy (RMS) continues to include best practice recommendations
• Exploring opportunities with agrichemical companies to increase the tools available to growers for implementing successful resistance management programs to control RLEM
• Investigating opportunities to use biologically-based approaches for RLEM control, including but not limited to: biological molecules and extracts, native and introduced mite predators and parasites, entomopathogens, endosymbionts, etc.
• Gaining new knowledge in the biology and ecology of the RLEM (including understanding of the summer diapause cues) which would allow for the development of forecasting (seasonal and paddock risks) tools to increase grower confidence, discourage the use of ‘insurance applications’ of pesticides and facilitate pro-active control practices.

Outcome: By 2025, the impact of red legged earth mites in grain crops is reduced by 10% through the adoption of integrated management strategies incorporating biological, cultural and chemical options.

Outputs

Output 1: From July 2020, growers continue to minimise redlegged earth mite control failures, and the development and spread of insecticide resistance, using accurate RLEM resistance status information across the grains industry.

Detail:

• Active surveillance and mapping of RLEM resistance will provide information to enable growers to implement successful management strategies to minimise the impact of RLEM.
• Resistance surveillance information will be used to maintain the advice provided within the RLEM Resistance Management Strategy (and to be endorsed by CropLife Australia).

Output 2: By July 2025, growers have access to diverse approaches that can be implemented effectively for the management of redlegged earth mites across the grains industry, including improved physical, cultural, chemical and biological tools and technologies.

Detail:

• Opportunities for new agricultural chemical products identified and explored with potential registrants
• Opportunities for biologically based approaches identified and explored, including: biological molecules and extracts, mite predators and parasites, entomopathogens and endosymbionts.

Output 3: By July 2025, growers and their advisers are implementing well-timed, integrated management approaches for redlegged earth mites to derive maximum and sustained benefits that consider the seasonal threat posed by this pest.

Detail:

Improved knowledge of redlegged earth mite biology and ecology (including understanding of the summer diapause cues in RLEM) to:

• Identify and exploit weaknesses and vulnerabilities in the RLEM life cycle;
• Minimise unintended landscape impacts of control strategies (e.g. preservation of key mite predators and minimisation of off-target resistance development);
• Increase grower confidence in the implementation of management strategies and facilitate pro-active control practices through the development of forecasting (seasonal and paddock risk) tools.

Output 4: By October 2020, in consultation with the GRDC, develop and implement a Communication and Extension (C&E) Plan that will support coordination of messaging and development of C&E content throughout this investment.

Detail:

• The Plan to include a proposed timeline for delivery of opportunities for communication and extension of key information arising from this investment, including industry resources, information and extension activities, in conjunction with the GRDC C&E Team and Manager Pests.