Cereal disease update 2024

Cereal disease update 2024

Take home messages

  • Disease pressure in the 2024 season will likely be moderate to extreme, with carry-over of inoculum from 2023 crops on stubble (for example, septoria tritici blotch, net form net blotch) and volunteers (for example, rusts).
  • Disease pressure will depend heavily on conditions in spring.
  • Monitor for disease in all crops this season and have a plan to prevent and control disease.
  • Fungicide resistance is now common in cereal pathogens in South Australia and Victoria, so strategies to manage cereal diseases under fungicide resistance environments are required.

Background

In the past two seasons, diseases have impacted on cereal production in the southern region, resulting in high inoculum carry over into this season. Should the expected wetter spring conditions eventuate, growers will need to implement disease management strategies to limit disease impact.

Seasonal update

Limited rain during crop sowing in the southern region resulted in dry sowing, which affected germination and crop establishment. This also meant less conducive conditions for disease development, hence less reports of disease in the region to date. However, detections of stripe rust in wheat and net and spot form net blotch in barley were recently reported in the Western district, Wimmera and Mallee regions. These detections coincided with susceptible varieties and lack of up-front fungicides, demonstrating the vulnerability of susceptible crops to diseases. Further, this highlighted the potential for diseases to be a concern if the season is conducive hereafter. Therefore, proactive disease management is required through monitoring crops, ensuring the management strategy matches the varietal resistance, and applying appropriate fungicides at the required time.

Tools to predict and estimate disease risk

With the unpredictable nature of weather conditions, it is often difficult to estimate the effects of disease in each season. However, it is important that growers and their advisors have tools to predict likely disease risks and devise appropriate control measures, if required. Such tools can help growers be proactive rather than reactive with regards to disease management.

With the advent of technology, new tools have been developed to aid in prediction and better decision making with cereal disease management. Two such innovations in recent times include disease management apps and BioScout spore trapping technology.

StripeRustWM

StripeRust Wheat Management (WM) is a tablet-based app that has been developed to support in-crop decision making for the management of stripe rust of wheat. Launched by GRDC in 2020, StripeRustWM uses information, including variety resistance rating, plant growth stage, fungicide history, presence of rust either within the crop or the district, climatic conditions, expected yield and economics, to estimate potential losses.

An example from StripeRustWM is shown in Figure 1. In this case, a trace of stripe rust has been detected in a crop with a resistance rating of MS at the booting growth stage. The output from the app shows that a marginally higher net return would be expected if fungicide was applied to the crop once, compared with not spraying. The net return would probably be lower if the crop was sprayed twice.

Figure 1. The summary view from the StripeRustWM app comparing expected yield, loss to stripe rust and net return for the cases where fungicide is not applied, is applied once, or is applied twice.

Figure 1. The summary view from the StripeRustWM app comparing expected yield, loss to stripe rust and net return for the cases where fungicide is not applied, is applied once, or is applied twice.

BioScout spore trapping technology

Detecting airborne spores and understanding their concentration is foremost in mitigating the spread of cereal diseases. Early identification plays a vital role in implementing timely interventions, ultimately reducing economic losses and safeguarding crop yields. BioScout's advanced automated SporeScout system monitors airborne disease-causing fungi, such as rusts, in near real-time, providing data-based insights for sustainable and profitable production.

BioScout, sponsored by the GRDC, has recently established a nationwide airborne disease surveillance network to monitor the spread of diseases including cereal rusts and powdery mildew. Data from the units are freely available on BioScout’s online dashboard, with graphs containing the airborne spore concentrations of pathogens of interest reported daily. You can access the network at BioScout Please note that the detection of rust or powdery mildew is general in nature and specific types cannot be distinguished at this time.

Rust update for Southern region

Rust spores have been consistently detected across the BioScout network. Airborne quantities remain low (Figure 2) indicating that there are no major rust outbreaks in the regions covered by the network thus far.

Figure 2. Concentration of rust spores (spores/m3 air) across the Southern growing region from 11 June–19 July. Note: not all unit locations are shown in the x-axis. Please refer to the online network for a full list of colours corresponding to each location.

Figure 2. Concentration of rust spores (spores/m3 air) across the Southern growing region from 11 June–19 July. Note: not all unit locations are shown in the x-axis. Please refer to the online network for a full list of colours corresponding to each location.

Wheat stripe rust

Rust has already been observed in 2024 in Victoria. This highlights that there is a potential risk if the season becomes conducive for rust. The early rust on-set during 2022 and 2023, along with the favourable conditions for disease development, resulted in a damaging outbreak of stripe rust in many parts of Victoria and SA. Where control was inadequate, large yield losses due to stripe rust in wheat occurred.

Therefore, for in-season rust management during 2024:

  • monitor crops for stripe rust symptoms
  • use a current cereal disease guide to check resistance ratings of varieties planted
  • where susceptible varieties are sown, have a fungicide management plan for use
  • use the free StripeRustWM app; for iPads and tablets
  • submit a sample of rust to the national rust surveillance program monitored by University of Sydney to enable pathotype (strain) detection and development of future resistant varieties. Follow Australian cereal rust survey for instructions on how to submit a sample.

Septoria tritici blotch in wheat

Septoria tritici blotch (STB) has become the most widespread disease in Victorian and South Australian wheat crops, and yield and quality losses are now common in many parts. This is largely due to increased area of susceptible varieties, stubble retention and conditions conducive to disease. However, only limited reports of STB have been made this season, with detections mostly in the high rainfall zone of Victoria. This is partly due to the dry winter, late emerging crops and the long latent period of STB (the time taken from spore germination to symptom observation). STB usually has a latent period of 21–28 days at optimal temperatures 15–20°C but outside of these temperatures, STB may have longer latent periods of up to ~40 days, depending on the existing paddock conditions. Therefore, crops need to be actively monitored for symptoms on the lower leaves and, should symptoms appear along with conducive conditions, necessary control strategies should be implemented, considering the varietal resistance to avoid yield and quality reductions.

AgVic trials during 2023 demonstrated losses of up to 28% and 13% in susceptible varieties in the medium (Wimmera) and low rainfall (Mallee) regions, respectively (Table 1). Yield losses due to STB in the Mallee were reported for the first time. These trials clearly demonstrated the benefit of avoiding highly susceptible varieties in both the Wimmera and Mallee to reduce losses due to STB (Table 1).

Table 1: Septoria tritici blotch severity and grain yield of wheat varieties with (Max) and without (Min) disease at Longerenong (MRZ) and Kinnabulla (LRZ), Victoria, 2023.

Variety

Rating

Disease severityA                               (% leaf area affected) in Max. treatment

Grain yield (t/ha)

Longerenong

Kinnabulla

Longerenong

Kinnabulla

11 Sep Z59B

8 Sep Z59

Max.C

Min.

Loss (%)D

Max.

Min.

Loss (%)

LRPB Lancer

MS

10a

5a

5.87

6.16ns

5

5.14

5.15ns

0

Hammer CL Plus

MSS

27b

9b

5.21

6.19**

16

5.00

5.26**

5

Scepter

S

55d

27de

5.37

6.45**

17

5.21

5.77**

10

Calibre

S

58d

25cd

5.74

6.60**

13

4.76

5.44**

13

Razor CL Plus

SVS

70e

29e

3.87

5.35**

28

4.01

4.38*

8

LRPB Impala

SVS

42c

24c

4.88

5.76**

15

4.42

4.79*

8

P

 

<0.001

<0.001

      

Lsd (0.05)

 

7.3

2.76

      

AWithin column means with one letter in common are not significantly different (0.05). ** = statistically significant at 5% and * = 10%. BDate of assessment made andZadoks growth stage. C Max. = Maximum disease treatment (No disease control with 1kg STB infected wheat stubble); Min. = Minimum disease treatment (No stubble, Seed (Fluquinconazole 167g/L @ 300mL/100kg seed) + Foliar applied fungicide at Z31 (Epoxiconazole 500g/L @ 125mL/ha) + Z39 (Benzovindiflupyr 40g/L + Propiconazole 250g/L @ 500mL/ha)). D Yield loss % for each variety was presented as % yield decrease vs the minimum disease treatment.

Where susceptible (S) or worse rated varieties are grown, fungicides may be required to protect yield. Consistent with previous research, two fungicide applications (at Z31 and Z39) increased grain yield by 16% in Wimmera and 10% in Mallee (Table 2). Always rotate fungicides with different modes of action to slow fungicide resistance development (see section on fungicide resistance below for more details).

Table 2: Septoria tritici blotch severity (% leaf area affected) and yield loss in wheat (Scepter (S)) in response to fungicide treatments at Longerenong (MRZ) and at Kinnabulla (LRZ), Victoria, 2023.

Treatments

Longerenong

Kinnabulla

Disease severityA

11 Sep Z59

Grain yield (t/ha)

Yield gain %B

Disease severity

8 Sep Z59

Grain yield (t/ha)

Yield gain %

Untreated control

58d

4.78a

-

31c

4.98a

-

Seed

55d

5.08ab

-

31c

5.02ab

-

Foliar at Z31

33b

5.16ab

-

19b

5.36cd

7

Foliar at Z39

46c

4.93a

-

18b

5.22bc

5

Foliar at Z31 + Z39

30ab

5.45b

14

9a

5.49d

10

Seed + Foliar: Z31+Z39

26a

5.55b

16

9a

5.49d

10

P

<0.001

0.016

 

<0.001

<0.001

 

Lsd (0.05)

7.2

0.47

 

2.15

0.22

 

AWithin a column, means with one letter in common are not significantly different at 0.05. BYield gain % is the percentage yield increase vs the untreated control. Fungicide treatments on seed (Fluquinconazole 167g/L @ 300mL/100kg seed) or foliar (Epoxiconazole 500g/L @ 125mL/ha at Z31 and Benzovindiflupyr 40g/L + Propiconazole 250g/L @ 500mL/ha at Z39).

Net form net blotch (NFNB) in barley

Net form net blotch (NFNB) is a common foliar disease of barley in Victoria and South Australia due to the adoption of susceptible varieties (for example, RGT Planet (SVS) and Spartacus CL (S)). The disease has been sighted in early sown crops in the Wimmera and Western districts of Victoria. Most detections were made in susceptible varieties. Unlike STB in wheat, NFNB has a short latent period, so should spring conditions be wet, it can produce multiple infections leading to high disease pressure and yield reductions.

During 2023, AgVic trials in the Wimmera (Wallup) demonstrated losses of up to 18% in the susceptible variety RGT Planet (SVS) (Table 3) under conducive conditions. The partial resistant variety Titan Ax (MS) had less infection and no yield loss, again showing the benefit of avoiding highly susceptible varieties.

Fungicides will be an important part of NFNB control in susceptible varieties. But in 2023, seed-applied fluxapyroxad (an SDHI), the active ingredient in the seed treatment Systiva®, did not provide expected NFNB control due to resistance to this active. Likewise, field resistance and reduced sensitivity toward triazoles such as tebuconazole, propiconazole and prothioconazole are also increasing in frequency. Hence these fungicides may no longer be reliable options for NFNB control (see section on fungicide resistance below for more details). BASF also detected a mutation affecting the efficacy of strobilurin (Group 11) fungicides used for NFNB control in Yorke Peninsula, South Australia. But the extent of its distribution is currently unknown.

Best economic control for NFNB management in 2023 was provided by dual foliar application at Z31 and Z39 (Table 3). Earlier applications tend to provide most of the suppression in shorter season environments and later applications in longer high-rainfall environments.

Table 3: Net form net blotch severity (%) and yield gain in two barley varieties in response to different fungicide treatments at Wallup, Victoria, 2023.

 

Disease severityA (% leaf area affected)

RGT Planet (SVS)

Titan Ax (MS)

TreatmentB

RGT Planet (SVS)

Titan Ax (MS)

Z39

29/8

Z82

10/10

Z37

29/8

Z82

10/10

Grain Yield (t/ha)

Yield gain %B

Grain Yield (t/ha)

Untreated control

10

41e

3

1

4.41ab

-

5.79

Seed

9

34d

-

-

4.52ab

-

-

Foliar at Z31

2

23b

0

0

5.10de

18

5.99

Foliar at Z39

11

29cd

3

1

4.70bc

-

5.91

Foliar at Z55

11

29cd

-

-

4.32a

-

-

Foliar at Z31 + Z39

2

14a

0

0

5.22e

21

5.86

Seed + Foliar Z39

11

26bc

0

0

4.87cd

13

5.97

Seed + Foliar: Z31+Z39

2

12a

0

0

5.29e

22

6.24

P

<0.001

<0.001

<0.001

0.176

<0.001

 

0.464

Lsd (0.05)

3.23

5.90

0.53

ns

0.34

 

ns

AWithin a column, means with one letter in common are not significantly different at 0.05.BYield gain % based on percentage yield increase vs the minimum disease. Fungicide treatments on seed (Fluxapyroxad 333g/L @ 150mL/100kg seed) or foliar (Prothioconazole 210g/L +Tebuconazole 210g/L @ 300mL/ha)

Fungicide resistance

Resistance to fungicides is becoming an increasing threat to cereal crops across Australia. The status of resistance to fungicides in important cereal diseases is summarised in Table 4 and is based on work by the Fungicide Resistance Group (FRG) at the Centre for Crop and Disease Management (CCDM) and the University of Sydney’s rust program.

Table 4: Status of fungicide resistance and reduced sensitivity cases in Vic and SA cereal crops (Nov 2023).

 

StatusA

Disease

Group 3 (DMI)

Group 7 (SDHI)

Group 11 (QoI)

Barley

   

Powdery mildew

Lab detection

Not detected

Not detected

Net form net blotch

Reduced sensitivity

Field resistance

Reduced sensitivity (SA)

Spot form net blotch

Reduced sensitivity

Not detected

Not detected

Leaf rust

Reduced sensitivity

Not detected

Not detected

Wheat

   

Septoria tritici blotch

Reduced sensitivity

Not detected

Reduced sensitivity (SA)

Powdery mildew

Field resistance

 

Field resistance

     

ALab detection –Measurable differences in sensitivity of the pathogen to the fungicide when tested in the laboratory. Detection of resistance in the lab can often be made before the fungicide’s performance is impacted in the field; Reduced sensitivity – Some reduction in fungicide performance which may not be noticed in the field. Serves as a warning that resistance is developing in the pathogen. Increased fungicide rates as per registered labels may be necessary. Field resistance – Fungicide fails to provide an acceptable level of control of the target pathogen at full label rates.

Fungicide resistance management

There are five strategies that growers can adopt to slow the development of fungicide resistance and therefore extend the longevity of the limited range of fungicides available:

  • avoid susceptible crop varieties
  • rotate crops
  • use non-chemical control methods to reduce disease pressure
  • spray only if necessary and apply strategically
  • rotate and mix fungicides/modes of action (MoA).

For more information on the management of fungicide resistance consult the ‘Fungicide Resistance Management Guide’ available from Afren. Following are the latest findings on fungicide resistance in Victoria:

Net form net blotch in barley

During 2023, following reports of poor NFNB control with fungicides, particularly fluxapyroxad (a member of SDHI, Group 7), the active ingredient in the seed treatment Systiva, and some compounds of DMIs (Group 3), eight samples from Victoria were sent to the CCDM for fungicide resistance testing. Six samples were positive for the C-S135R mutation (the second-highest levels of resistance to fluxapyroxad of the SDHI mutations found in Australian NFNB). Further testing showed that 41% and 22% of isolates grew on the highest dose of tebuconazole and fluxapyroxad, respectively (Table 5). This indicated the failure to provide disease control at the maximum label rate of these chemicals. Hence, strategies to manage NFNB under fungicide resistance environments are urgently needed.

Table 5: Percentage of isolates of net form net blotch showing sensitivity/resistance to DMI (Group 3) and SDHI (Group 7) fungicides in Victoria during 2023.

Response

DMI (Group 3)

SDHI (Group 7)

Sensitive

54%

41%

Reduced sensitivity

5%

37%

Resistant

41%

22%

Septoria tritici blotch in wheat

Based on historic studies by NSW DPI, it is known that reduced sensitivity to the DMI (Group 3) fungicides is well established in Victoria. Work is required to establish the current status of resistance to these fungicides in Victoria.

The finding of resistance mutations to strobilurin fungicides (Qol, Group 11) in two STB samples collected in South Australia during 2020 was very concerning. In vitro testing showed a 200-fold increase in resistance to azoxystrobin compared with the susceptible strain. Fortunately, testing of 25 samples collected from Victoria during 2023 did not detect this mutation, suggesting that it is still rare. Therefore, use of strategies to slow selection of this mutation are critical.

Conclusion

In the absence of proactive disease control, yield losses can be greater than 20% in seasons with favourable conditions. It is, therefore, important that plans are developed to effectively manage cereal diseases this season. Disease management plans should reflect variety resistance and seasonal conditions, and where the risk warrants it, the proactive and prudent use of fungicides, avoiding overuse to protect their longevity.

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. Funding for this work was provided by the Victorian Government (Agriculture Victoria) and the GRDC through the GRDC projects: DJPR2104-004RTX, DAQ2304-008RTX, DAW2112-002RTX and CUR2302-002RTX. Thanks to Agriculture Victoria’s Field Crops Pathology Team. Thanks also to the Birchip Cropping Group for field trials within the Victorian Wimmera and Mallee and to our research collaborators Drs Mclean (Project Platypus/AgVic), Milgate (NSW DPI), Taylor (University of Adelaide) and Garrard (SARDI).

Useful resources

Cereal disease guide

Australian cereal rust survey

Septoria tritici blotch in wheat fact sheet

Fungicide resistance

Contact details

Hari Dadu
Agriculture Victoria
Private Bag 260, Horsham VIC 3401
03 5450 8301
Hari.Dadu@agriculture.vic.gov.au
@Imharidadu

GRDC Project Code: DJP2104-004RTX; DJP1905-002SAX; DJP2103-005RTX; DAQ2304-008RTX; DAW2112-002RTX; UOS2207-002RTX; CUR2302-002RTX; BIS2305-001RTX,