Cropping

Be alert for triple-fungicide-resistant barley net form net blotch

By Sophie Baldwin

Aug 26, 2025

NFNB has the potential to reduce barley yield by up to 40 per cent.

Barley growers in Victoria should keep watch for signs of net form net blotch (NFNB) disease following the recent confirmation of a triple-fungicide-resistant mutant of NFNB at Streatham.

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Agriculture Victoria cereal pathologist Dr Hari Dadu says the NFNB mutant was discovered after a suspected fungicide resistance sample of RGT Planet barley was sent to the Centre for Crop Disease Management (CCDM) for analysis.

This NFNB mutant may have existed for several years prior to its detection.

“This mutant form of NFNB is resistant to several active ingredients within three different kinds of fungicide: Group 3, Group 7 and Group 11,” Dr Dadu says.

“NFNB has the potential to reduce barley yield by up to 40 per cent, as well as impacting grain quality, so resistance to key active ingredients within the three main fungicide groups used to control the disease is very concerning for growers.”

He says the net form net blotch starts as pinpoint brown lesions, which elongate and produce fine, dark brown streaks along and across the leaf blades, creating a distinctive net-like pattern.

Older lesions continue to elongate along leaf veins and often are surrounded by a yellow margin.

Dr Dadu warned growers this new mutant form of NFNB might also be more widespread than first thought.

“Fungicide resistance to Group 3 and 7 fungicides has been around for several years and was again confirmed during 2024 in barley samples collected from Inverleigh, Hamilton, Horsham and Kaniva,” he explains.

“Growers of susceptible barley varieties and, in particular, RGT Planet and Zena CL, should monitor crops closely and if they suspect new forms of resistance contact crop-safe@agriculture.vic.gov.au”

Growers should review their integrated disease management processes and take the following proactive steps to reduce the spread of the NFNB mutant:

Select and sow less susceptible barley varieties using Agriculture Victoria’s (agriculture.vic.gov.au/biosecurity/plant-diseases/grain-pulses-and-cereal-diseases/cereal-disease-guide).
Do not sow Planet-type barley for one to two seasons.
Rotate crops.
Manage stubble to reduce disease carryover.
Ensure the green bridge of volunteer plants between seasons is removed.
Follow best practice fungicide management such as mixing and rotating fungicide groups and strategic timing of fungicide applications as advised by the Australian Fungicide Resistance Extension Network (AFREN).

The cereal disease guide and further information on NFNB is available at agriculture.vic.gov.au/biosecurity/plant-diseases/grain-pulses-and-cereal-diseases

By Sophie Baldwin