When central Victorian grain grower Ian Martin found brown marks on the leaves of his LRPB Trojan (PBR) wheat, he suspected Septoria tritici blotch (STB) had crept into his 2023 crop.

He had planned to sow Big Red variety on a 310-hectare outlying block near Mount Beckworth, but after wet weather kept him off his high-rainfall zone plot through April he made the “on the run” decision to plant the shorter-season Trojan (that he had stored for a couple of years instead.

Knowing Trojan’s susceptibility to STB (and stripe rust), he applied seed dressing penflufen (EverGol® Prime), as well as flutriafol (Impact®) to the fertiliser. But continuing inclement weather delayed the rest of his fungicide regime. Azoxystrobin and epoxiconazole (Tazer® Xpert) was applied later than he would have liked at growth stage 32, and prothioconazole and bixafen (Aviator® Xpro®) 34 to 35 days after that.

So when he saw the invitation to bring a crop sample for testing by the Australian Fungicide Resistance Extension Network (AFREN) team at the Field Applied Research (FAR) field day held at the Victorian Crop Technology Centre in October, he jumped at the opportunity.

Ian’s interest was twofold: he wanted to see how his stored grain had held up against potentially evolving pathogens, and also whether he would need to think about changing his approach to fungicides for the remainder of the season and the years ahead.

“Being an older variety, I was interested to see whether it still stacks up, so I thought I’d bring it down to see if there was any disease or resistance and whether I’d need to change any chemistries down the track,” he says.

On-site testing

The fungicide resistance sample testing workshop was one of a number of AFREN activities that have been bringing technology out of the lab and into the field.

Using state-of-the-art portable technology, AFREN scientists from Curtin University’s Centre for Crop and Disease Management (CCDM) test samples onsite, providing insights around disease and fungicide resistance within hours.

AFREN project coordinator Dr Anna-Sheree Krige explains that the portable technology works by comparing DNA extracted from diseased plant samples with markers for particular diseases.

It then produces a digital graph that shows whether the pathogen’s DNA contains any mutations that make it less susceptible to fungicides. “With this technology we can detect pathogens and from those pathogens determine if there are any mutations that are associated with fungicide resistance,” Dr Krige says.

Benefits of engagement

Taking the technology into the field is beneficial in a number of ways, she says.

The practical service to growers not only provides definitive information on whether they have a disease or resistance issue to deal with, but also enables researchers to discover first-hand which diseases and resistance are emerging on the ground in different parts of the country.

The AFREN team also has the opportunity to build awareness of issues and spread the message about how to prevent fungicide resistance, which Dr Krige says is an ongoing duty of AFREN across Australia’s cropping regions.

Of notable concern, she says, is resistance against chemistries to control diseases such as: net form net blotch (NFNB) in barley across all growing regions and especially South Australian and Western Australian high-rainfall zones; Septoria tritici blotch (STB)  in wheat, particularly in the high-rainfall areas of the southern growing region; and wheat powdery mildew (WPM), a disease that emerges in conducive conditions and has been a significant challenge for growers in the Southern region in recent years..

“Fungicide resistance is a real problem and we can give growers and agronomists management strategies directly that, if incorporated on a wider scale, will reduce it,” she says.

Management strategies

AFREN with the support of GRDC has developed key management strategies to combat fungicide resistance. Coined the ‘Fungicide Resistance Five’ they begin with building a solid foundation by selecting less-susceptible varieties; continue with management strategies such as crop rotations; and finish with astute fungicide management including strategic application and changing fungicide groups, modes of action(MoA).

Dr Krige says that ideally fungicides would be the last option for disease management after crop selection and rotation and other non-chemical strategies.

“Rotating crops and MoA reduces the risk of resistance by helping to ensure the pathogen can’t easily adapt to the cropping conditions,” she says. “And holding workshops and testing services allows us to see what is happening and spread this messaging directly to try to reduce resistance development in the future.”

Negative and positive results

For Ian Martin the news was positive – his sample tested negative to STB and therefore showed no signs of fungicide resistance. This, he says, was a relief and testament to the approach he has taken to his fungicide regime on the advice of FAR managing director Nick Poole, particularly around the timing of applications.

“It’s great to see the strategy working,” says Ian, who found the information around fungicide MoA and other management strategies provided by AFREN at the field day of significant value. “It’s fantastic to be able to talk to the best people in the industry, doing all the hard work behind the scenes, who will give information freely and you can ask them any question you want,” he says.

He was also pleased to contribute to the bigger picture of fungicide resistance.  And while his sample was clear, other testing from the trial site itself turned up some results that showed the implications of resistance.

In some plots where crops were grown under high NFNB pressure to test for the efficacy of particular fungicide strategies, the analysis detected a “high frequency of a mutation conferring SDHI (Group 7) resistance”, Dr Krige says. This mutation was found in a trial that had received two Group 3 (DMI) applications, in addition to treatments incorporating SDHI and QoI (Group 11) fungicides. The high level of disease observed after these trial treatments also indicates the potential presence of DMI resistance, which will need to be confirmed with further laboratory testing.

Dr Krige says the presence of this SDHI resistance mutation, verified by further testing at the CCDM laboratories in Western Australia, indicated how vulnerable crops are to diseases when fungicides do not work optimally.

“It shows that fungicide resistance is a very real issue and a very real concern – and proper management practices will be imperative to prevent more cases of fungicide resistance,” she says.

More information: Dr Anna Sheree Krige, sheree.krige@curtin.edu.au

To find out about Workshops being provided by AFREN in 2024  go to GRDC Events.