Farmers to benefit from new tools for sustainable redlegged earth mite control

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There are few things that connect farmers like their disdain for redlegged earth mites.

This common pest is one of the most destructive and economically important in the pasture and cropping sectors throughout southern Australia.

With the evolution and spread of redlegged earth mite (RLEM) resistance to the most effective and widely used insecticides, management options must be reassessed.

AgriFutures Australia Pasture Seeds Program has co-funded a project with the Grains Research and Development Corporation (GRDC) to address “future options for the control of RLEM in Australian crops”, extending this research to pasture seed producers.

Key components of the AgriFutures Pasture Seeds project:

  • Broadscale RLEM resistance surveillance
  • Exploration of novel synthetic and biological based approaches to RLEM

 

Initially, the project led by Cesar Australia is surveying farmers and agronomists to better understand how RLEM is managed, including their attitudes towards the pest and the damage it’s inflicting in the paddock.

Complete the survey

This survey will provide an industry RLEM knowledge baseline, the foundation to which best practice control strategies, such as integrated pest management guidelines and resistance management recommendations, will be developed.

More management options needed

Cesar Australia Research and Extension Scientist, Leo McGrane, said the evolution of RLEM resistance to synthetic pyrethroids and organophosphates means farmers are left with fewer control methods.

He said surveying growers and agronomists, asking how they navigate the complexity of insecticide resistance, will provide insights into RLEM management in different farm systems.

“We are hoping to get an understanding of exactly how they have managed RLEM in the past, whether they’ve had success controlling it and what exactly made it successful in the cases where they were able to manage it,” he said.

“For example, did they use a specific chemical? Or is the mite simply not an issue on their farm? If so, why might that be the case? Are they doing something a bit differently?”

The Australian agricultural industry has management guidelines and strategies for RLEM, including controlling the pest in circumstances where there’s known insecticide resistance.

Mr McGrane said this new industry survey would provide information to update these guidelines and strategies, while also enabling researchers to tailor future research to address current RLEM challenges.

The on-farm toll

Natalie Allen is a farmer and agronomist at Western Ag in South Australia’s south east.

Following suspected RLEM resistance to synthetic pyrethroids, she’s sent samples from lucerne pasture from her family’s grazing property at Tintinara, to Cesar Australia for testing.

Unfortunately, resistance to chemical control has started developing in this region during the past two to three years, according to Ms Allen.

“It’s a big concern, we don’t really have a plan B in available insecticides,” she said.

“One strategy being used is to plant early and higher plant numbers and try to rotate chemicals – integrated pest management strategies.”

“When growers are establishing pastures, they like to monitor the pasture establishment and spray when necessary, so resistance doesn’t become an issue.”

Ms Allen said updated RLEM management strategies and guidelines, outlining best practice, could provide farmers with more certainty about achieving a return on their investment in new pastures.

“It might give us some confidence moving forward that when we spend money, it will be to make money,” she said.

Scott Hutchings is an agronomist at Cox Rural in Keith, South Australia.

He said RLEM had caused issues for farmers establishing annual pastures, legume-based crops, and canola – particularly in the sandier, lighter soils throughout the region.

Insecticide resistance was also a developing concern.

“We have some confirmed resistance and some suspected resistance in the district,” said Mr Hutchings.

“There’s confirmed resistance to alpha-cypermethrin (a synthetic pyrethroid), dimethoate and omethoate (both organophosphates).”

“It will become an increasing issue for us, because there’s very little else registered for use, there’s only a couple of chemical groups registered for control of RLEM by the APVMA.”

Chemical concerns

With so few insecticide management tools, it’s difficult – especially for farmers growing pasture – to avoid chemicals that RLEM have evolved resistance to.

Part of the project that AgriFutures have contributed to will investigate new synthetic insecticide options for controlling RLEM and potential biological extracts, the latter Leo said would hopefully be a “softer option” for beneficials than current chemical options.

RLEM surveillance testing this year, which is also being co-funded by AgriFutures, has been conducted in Western Australia, Victoria and some areas of South Australia, searching for the emergence of any additional resistance.

In Victoria, RLEM have only been found to be resistant to organophosphates, but in Western Australia and South Australia there’s confirmed resistance to synthetic pyrethroids, as well as organophosphates.

Developing alternative control options for RLEM is important research, according to Mr McGrane. It will not only limit the evolution and spread of resistance in the mite, but it will make sure it’s possible to manage it into the future.

“If we continue to manage it by prophylactically applying insecticides, resistance is likely to increase across southern Australia and this along with the very limited control options would make it even more difficult to control,” he said.

“If we can produce research and come up with alternative control strategies, we can safeguard the effectiveness of the current chemical control options.”

The first step is for farmers and agronomists to complete the RLEM survey.

“This survey is a crucial part of this project, it will help us develop extension materials and promote the new resistance management strategy and best management practice information so that growers understand it and have easy access to it,” said Mr McGrane.

To complete the survey visit  http://go.unimelb.edu.au/4myi

 

How does RLEM chemical resistance happen?

Chemicals have been the most effective and widely used control option for RLEM. But an overreliance on a small number of chemical groups has led to the evolution of insecticide resistance to these chemicals in the RLEM.

Cesar Australia Research and Extension Scientist Leo McGrane said resistance between chemical groups varied.

Resistance to organophosphates in RLEM is thought to be metabolic. This means that RLEM can have varying levels of resistance, from low to moderate, against organophosphates. Growers may not realise they have organophosphate resistance because they are achieving some level of control with certain OPs in their paddocks. However, repeated exposure of OPs to an OP resistant RLEM population will increase the selection pressure for resistance to increase.

But for the other main chemical group used to control RLEM – synthetic pyrethroids – once a RLEM population has evolved resistance to this chemical, control simply won’t work at all. This is known as knockdown resistance (kdr), and it confers an extremely high level of protection in RLEM, exceeding 200,000-fold resistance against some synthetic pyrethroids.

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