Fungicide resistance concerns raised

Image of Dr Andrew Milgate

New South Wales Department of Primary Industries senior research scientist Dr Andrew Milgate.

PHOTO: Nicole Baxter

A plant pathologist has raised concerns about root disease build-up in farming systems and the long-term sustainability of some commonly used fungicides.

New South Wales Department of Primary Industries senior research scientist Dr Andrew Milgate says the pathogen Zymoseptoria tritici, responsible for causing the cereal disease septoria tritici blotch (STB), is common in the high-rainfall areas of Victoria, South Australia and Tasmania.

He says the disease is a threat to early sown cereals in high-rainfall areas because of changes detected in variety resistance and the discovery of fungicide resistance developing in the pathogen.

“Also STB has a long spore dispersal mechanism, which means ascospores released from stubble during autumn in Victoria, for example, can blow onto and infect emerging wheat in Victoria and southern NSW,” he says.

Image of septoria tritici blotch on a leaf

Septoria tritici blotch (and in photo below).


Dr Milgate, who is based at the Wagga Wagga Agricultural Institute, says research to date is showing the most serious levels of fungicide resistance are being encountered in Tasmania.

He and his team have also confirmed a small number of isolates in NSW containing mutations in the CYP51 gene that reduce sensitivity to triazole fungicides.

“Resistance levels detected across Victoria, South Australia and NSW show most fungicides will still be effective in the paddock,” he says.

“To maintain the effectiveness of these fungicides we encourage the use of multiple management strategies against the disease.”

Dr Milgate suggests reducing the selection pressure for further mutations and extending the life of available fungicides by mixing or alternating the use of different azole fungicides.

“Not all azole fungicides are affected equally by mutations of the STB fungus, which means that products that combine azoles such as Tilt® Xtra (propiconazole and cyproconazole) or Impact® Topguard (tebuconazole and flutriafol) that have a registration for STB could be used this way,” he says.

Image of septoria tritici blotch on a leaf

“Equally, in crops where two fungicide applications are to occur (at GS31 and GS39), the same active should not be used at both applications. Repeated applications of the same active ingredient have been shown to increase the rate at which the pathogen develops resistance.”

To manage STB in wheat, Dr Milgate says limited fungicides are available with different modes of action.

“Several products combine a strobilurin with an azole and these may provide some benefits in delaying or reducing the risk of resistance development,” he explains.

“However, the strobilurins on their own are considered to be at high risk of developing resistance because of their single site mode of action. In some countries, resistance to strobilurins is so widespread in the STB population they are no longer recommended as effective, even in mixtures.”

In addition to mixing or rotating fungicides, Dr Milgate says an integrated approach to disease control that includes crop rotation, stubble removal and avoiding susceptible varieties will reduce inoculum loads and delay the onset of fungicide resistance while also prolonging variety resistance.

More information:

Dr Andrew Milgate,
02 6938 1990,


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