Variety helps fight resistance

SARDI crop pathology researcher Hugh Wallwork gave a cereal disease update at the recent GRDC Grains Research Update in Adelaide.

He outlined that observations on the Yorke Peninsula had shown resistance to fungicides had developed in net form net blotch in barley, as well as powdery mildew in wheat.

"Graingrowers need to be careful when selecting varieties and fungicide applications this season," he said.

One particular change is a loss of efficacy to some succinate dehydrogenase inhibitor (SDHI) products, including Systiva, that has been commonly used for control of NFNB.

Dr Wallwork said in observations on the lower YP in July, some Spartacus crops that had been treated with Systiva were found to be severely affected by NFNB.

"It was at such high levels that indicated the treatment had little effect," he said.

"The crops had been sown into Spartacus stubbles from a previous crop which also had a Systiva treatment - so Spartacus with Systiva had followed Spartacus with Systiva.

"Essentially, people need to try and avoid using some SDHIs on these areas this coming year, and possibly in the next, so that we can try and bring them back into use again at a later date."

Dr Wallwork said fungicide resistance researcher Fran Lopez, from the Centre for Crop and Disease Management and Curtin University, was enlisted to do a survey across the YP into possible NFNB resistance.

"The survey showed a high level of resistance to fluxapyroxad right throughout the area," Dr Wallwork said.

"Add in any moderate resistance cases and it took up a large area of the YP.

"(Dr) Lopez also looked into resistance to other fungicides and found high levels of resistance to tebuconazole and possibly other DMI (demethylation inhibitors) products as well.

"We are still waiting to find out what the effects of other DMI fungicides on these isolates are.

"But essentially, some SDHIs are not working on the lower YP because of back to back use."

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Dr Wallwork said while the testing was only undertaken on the YP, he was confident airborne spores had made this a statewide problem.

"There is no reason why it wouldn't be happening to some degree all over the state albeit at a lower level," he said.

"So growers should be monitoring their crops carefully this coming year and report any problems.

"The pathogen adapts to varieties being more commonly grown and the shift can be quite fast.

"By growing a lot of Spartacus on the YP, virtually a monoculture in some places, the pathogen has adapted to being virulent on this variety.

"Compass and Spartacus were both MRMS (moderately resistant to moderately susceptible) to NFNB when they were released.

"But over time, as they have been grown more widely, they have become more susceptible.

"Maritime and Fleet had more dramatic changes. These varieties, initially very resistant, became highly susceptible after their release.

"But as they have not been grown in recent years they are now showing good resistance again as the fungus has adapted to newer varieties.

"So we can actually change this pathogen by what we grow in the paddocks."

To combat potential net form net blotch resistance to certain fungicides, SARDI's Hugh Wallwork advises growers to "mix varieties up, not just for this disease, but for all of them".

"A monoculture of one variety is asking for problems, barley on barley or wheat on wheat - you might get away with it one year, but you are causing problems in future years," he said.

Research on the Yorke Peninsula, where the problem has arisen, showed older barley varieties of Schooner, Sloop and Scope were among the more resistant to NFNB, while Commander and Fathom were among the most susceptible.

Dr Wallwork said one feed barley tested "really well".

"Rosalind is the best thing we have tested other than Scope - we may have to study it more to help produce more resistant varieties," he said.