Barley diseases – what to be on the lookout for

Barley diseases – what to be on the lookout for

Take home messages

  • Seasonal conditions in 2022 are shaping up to be conducive for barley foliar disease.
  • The southern region now has NFNB resistance to SDHIs and reduced sensitivity in SFNB to SDHIs.
  • Surveys for fungicide resistance are ongoing and agronomists are encouraged to notify pathologists of any suspected cases and submit samples for testing.
  • Updated information is available from the AFREN website.

Background

The 2022 growing season is shaping up to have wetter seasonal conditions than have been experienced in recent years. If above average rainfall continues in late winter and early spring, then seasonal conditions will put growers at risk of experiencing losses due to foliar disease pressure.

Management strategies for barley foliar diseases net form net blotch (NFNB), spot form net blotch (SFNB) and barley scald need to be considered for implementation this season. Up to date understanding of current fungicide resistance status for these pathogens is critical to achieving sufficient disease control.

The Australian grains industry now has several cases of fungicide resistance in pathogens causing barley foliar disease that are either currently affecting or threatening southern region growers. Currently, the main concern in the region is SDHI and DMI resistance and reduced sensitivity to NFNB and SFNB.

Effective disease management strategies can still be implemented for these diseases as part of integrated disease management, and growers are encouraged to be aware of which fungicide modes of action need to be avoided due to reduced sensitivity or resistance.

Methods

Fungicide resistance prevalence

Data contributing to our understanding of the prevalence of fungicide resistance is obtained from the collection of diseased leaf samples sent to the Centre for Crop Disease Management (CCDM) Fungicide Resistance laboratory. Samples are collected by growers, agronomists, and pathologists either when fungicide resistance is suspected in a paddock, or through targeted surveys. CCDM conduct the analysis for fungicide resistance by both molecular and culture phenotype methods. Sample results are reported as either lab detection (detected in lab but no evidence of field failure), reduced sensitivity (for DMIs and SDHIs only), or resistance (indicating complete fungicide resistance).

Targeted surveys were conducted during 2019 for barley NFNB when SDHI resistance was first detected on the Yorke Peninsula (YP) and samples from other regions have been submitted in subsequent seasons. In 2021, a series of NFNB and SFNB samples from Victoria were processed.

Results and discussion

Fungicide resistance prevalence

Fungicide resistance is now prevalent across all grain growing states in Australia. Figure 1 shows which states have recorded fungicide resistance and the associated crop, disease and fungicide group. The legend also indicates if the detection is lab detection, reduced sensitivity or complete resistance. In barley crops in Victoria, resistance is present in group 3 and 7 for NFNB, group 3 for SFNB, and group 3 for barley powdery mildew, as of July 2021.

However, additional samples processed in 2021 from eastern Victoria also showed reduced sensitivity to group 7s in SFNB (Table 1.)

Barley disease samples from Victoria in 2021 processed by CCDM showing SDHI resistance and reduced sensitivity in NFNB (PtSdhC-H134R and PtSdhD-D145G), SDHI reduced sensitivity in SFNB (PtmSdhC-N75S) and DMI reduced sensitivity in NFNB and SFNB (F489L).

Figure 1. Prevalence of fungicide resistance across Australia in grain crops. Figure produced by AFREN.

Table 1: Barley disease samples from Victoria in 2021 processed by CCDM showing SDHI resistance and reduced sensitivity in NFNB (PtSdhC-H134R and PtSdhD-D145G), SDHI reduced sensitivity in SFNB (PtmSdhC-N75S) and DMI reduced sensitivity in NFNB and SFNB (F489L).

    

DMI Mutations

SDHI Mutations

  
    

Reduced sensitivity

Resistance

Reduced sensitivity

  

Location

State

Cultivar

Pathogen Present

NFNB + SFNB

NFNB

NFNB

SFNB

  
  

Unknown

Vic

Spartacus

NBNB + SFNB

+

+

-

-

  

Banyena

Vic

Spartacus

NFNB

+

+

-

+

  

Banyena

Vic

Spartacus

NFNB

+

+

-

+

  

Minyip

Vic

Spartacus

NFNB + SFNB

+

+

+

-

  

Minyip

Vic

Maximus

NFNB + SFNB

+

+

-

-

  

Horsham

Vic

Unknown

NFNB + SFNB

+

-

-

-

  

Horsham

Vic

Unknown

NFNB

+

+

+

-

  
          

Key

      

+

Resistance mutation detected

      

-

Wild-type only detected

      

Barley net form net blotch

In 2019, SDHI fungicide resistance to barley NFNB was detected near Minlaton on the southern YP of SA. Targeted surveying by CCDM and SARDI determined the resistance to be prevalent throughout the mid and southern YP. Additionally, DMI resistance was detected in many of the samples, identifying the presence of dual SDHI and DMI fungicide resistance. The SDHI resistance was detected from the use of fluxapyroxad as a seed treatment, where barley had been grown for the previous two years, with fluxapyroxad used as a seed dressing in both years.

Since 2019, SDHI resistance has been detected in multiple locations on the Eyre Peninsula, in the Mid North and the South East regions of SA. At the end of the 2021 growing season, SDHI resistance had also been detected in the North West of Victoria (Table 1, PtSdhC-H134R mutation). There are currently three separate mutations identified causing the SDHI resistance in NFNB, indicating there are multiple separate occurrences of resistance development.

Reduced sensitivity has also been detected to the DMIs tebuconazole and propiconazole in NFNB in Victoria.

Barley spot form net blotch

In Western Australia, DMI resistance in SFNB has been present for several years. In 2020, SDHI fungicide resistance to SFNB was also detected in WA. Reduced sensitivity to tebuconazole (group 3) has been detected in SA and Victoria. Table 1 shows the reduced sensitivity to SDHIs (group 7) that was detected in SFNB (PtmSdhC-N75S mutation) in Banyena, Victoria in 2021.

Barley powdery mildew

Resistance and reduced sensitivity have been detected to group 3 fungicides in WA. In all states, excluding SA, a mutation has been detected in the target site affecting group 3 fungicides. This is currently a lab detection only but could pose a risk to field effectiveness.

Barley scald

To date, no fungicide resistance has been detected in this pathogen and reduced efficacy of fungicides should not be detected. If resistance is suspected in this pathogen, please contact your local barley pathologist for information on resistance testing.

Managing disease where fungicide resistance is present

Managing fungicide resistance will continue to play an increasingly important role in on-farm decision making as the situation develops in Australia. Growers need to have a good understanding of the disease pressures in their area, as well as any fungicide resistance that is currently present or posing a substantial threat of entering their region.

Integrated disease management (IDM) is essential in successfully controlling disease and the importance of this approach only increases where fungicide resistance is present. The pyramid in Figure 2 illustrates the importance of variety selection and IDM in fungicide resistance management, as these factors should be considered before planning fungicide strategies. The largest emphasis should be placed on variety selection, as varieties that contain some level of resistance to the disease provide the strongest and most economical protection.

The Mallee region of Victoria is prone to net blotch infections, particularly SFNB. Seasonal conditions to date are conducive for disease pressure of these diseases and others, such as barley scald, to increase. In susceptible or very susceptible varieties, yield losses due to SFNB can be expected in crops of 2t/ha or more.

Growers that have used SHDI-based seed dressings such as Systiva® will need to be aware that resistance or reduced sensitivity may be present and consider management plans for the remainder of the season. Fungicide modes of action need to be rotated and groups 11 and 7 should only be used once per growing season. In group 3 fungicides, each active should only be used once per season.

Once fungicide resistance is present within a paddock, it may not be apparent in the first one to two seasons, and the affected active chemistry may continue to be effective at a paddock scale. This is because pathogens causing diseases such as net blotches, powdery mildew and septoria tritici blotch (STB) are sexually reproducing, which can enable genetic recombination. When fungicide resistance first affects a paddock, it may only be present in a small percentage of the pathogen population, allowing the rest of the sensitive pathogen population to respond to the fungicide. It can take two or more years for the resistant portion of the population to become the dominant portion, and for field failure of the fungicide to be observed.

Fungicide resistance management pyramid produced by AFREN.

Figure 2. Fungicide resistance management pyramid produced by AFREN.

Conclusion

IDM plays a crucial role in fungicide resistance management and a better understanding of how endemic diseases interact with our environment. This paper provides growers and advisers with up-to-date information on which fungicide resistances are present in barley in the southern region. Resistances of most concern in the region are NFNB resistance to SDHIs, and NFNB and SFNB reduced sensitivity to SDHIs and DMIs.

Growers can manage fungicide resistance by knowing which resistances are present in their region, selecting varieties with genetic resistance, using IDM strategies, and strategically applying fungicides. Fungicide applications should be limited to spraying only when necessary, avoiding actives if there is resistance in your region, rotating modes of action, using only one active once per season, and using mixtures where possible.

Acknowledgements

The research undertaken as part of this project is made possible by the significant contributions of growers through both trial cooperation and the support of the GRDC, the authors would like to thank them for their continued support. The authors would also like to acknowledge the rest of the AFREN team and the Fungicide Resistance team at CCDM.

Useful resources

The Australian Fungicide Resistance Extension Network

Cereal Variety Disease Guide 2022

Cereal Seed Treatments 2021

Fungicide resistance in barley

Contact details

Tara Garrard
SARDI
2A Hartley Grove, Urrbrae SA 5064
0459 899 321
tara.garrard@sa.gov.au
@TaraGarrard

GRDC Project Code: CUR1905-001SAX, UOA2003-008RTX, DJP2003-001RTX,