Cereal disease update for Yorke Peninsula 2021

Take home messages

  • Avoid growing barley on barley.
  • Avoid reliance on fungicides by growing varieties with better resistance.
  • Rotate and/or combine different classes of fungicides for control of net blotches and wheat powdery mildew.
  • Avoid fluxapyroxad (Systiva®) for the time being.

Background, results and discussion

Barley net form net blotch

The net form net blotch (NFNB) fungus has been evolving rapidly in South Australia since the 1990s when it first showed up in the state after a lengthy absence. Initially it was observed with virulence on just a few key varieties including Franklin, Skiff and then Barque. Then in 2007 and 2008 it acquired virulence on Keel, then Maritime and consequently spread dramatically across the state. Since 2012 we have been monitoring the virulence of the pathogen in SA each year using 24 key varieties. Results from this monitoring have shown a constant erosion of resistance over time with some varieties gradually losing resistance as minor genes have been overcome, whilst other varieties showed much larger, sudden increases in susceptibility. Until 2020 the older varieties Clipper, Schooner, SloopSA and Scope showed good resistance to all isolates collected and so we identified these varieties as having durable resistance. Last year however one isolate from Bute and several from Western Australia showed virulence on all four varieties whilst a few other isolates showed virulence on one or more of them. The reason for this sudden shift is not apparent.

At the same time, the NFNB population has also been evolving resistance to some fungicides, notably the seed treatment Systiva®. In 2019 we observed 3 paddocks with a high degree of NFNB infection south of Minlaton. In each case Spartacus was sown with Systiva® seed treatment into stubbles of a Spartacus crop that had also been treated with Systiva® in 2018. This was clearly a situation where very high selection pressure was brought to favour any mutations towards increased virulence on Spartacus as well as resistance to Systiva®. Molecular tests conducted by Curtin University revealed the Systiva® resistance mutation in samples from each paddock. Further tests also revealed resistance mutations present across the lower Yorke Peninsula in 2019 (Figure 1) as well as in two isolated spots at Lock on the Eyre Peninsula and at Kybybolite in the South East. Interestingly samples from the latter two sites had quite different mutations to the Yorke Peninsula samples indicating quite separate evolution of resistance at each location.

In 2020 resistance to Systiva® was found to be commonplace on the West Coast of the Eyre Peninsula as well as being present at Avon on the Adelaide Plains. In June this year we have been advised that Spartacus treated with Systiva® is showing high levels of infection near Ouyen in Victoria. Again, this crop was sown into stubbles of Spartacus that had also been treated with Systiva® in 2020.

Table 1. Net form net blotch isolates from SA in 2018 tested on 24 barley varieties. A high number indicates high level of susceptibility.

Isolate49/1850/1851/1852/1821/1874/1825/18a69/1870/1871/1875/1873/18a76/1872/18a

Host

Keel

RGT Planet

Topstart

RGT Planet

RGT Planet

RGT Planet

Keel

Gairdner

La Trobe

Compass

Rosalind

Westminster

Oxford

Fatima

 

Elliston

Elliston

Wanilla

Wanilla

Yeelanna

Yallunda Flat

Brentwood

Conmurra

Conmurra

Conmurra

Rendelsham

Rendelsham

Rendelsham

Rendelsham

Clipper

3

4

3

2

4

3

2

3

4

4

3

2

2

2

Schooner

4

3

2

3

4

2

2

3

2

4

2

2

3

2

Scope

2

2

2

2

2

2

2

2

2

3

2

2

2

2

Sloop SA

2

2

2

2

5

2

2

2

2

2

3

2

2

2

Alestar

3

5

8

3

7

5

4

3

3

3

7

8

8

7

Banks

2

1

2

1

2

1

2

6

1

2

2

2

2

2

Commander

7

6

5

6

8

4

9

6

5

7

4

3

9

6

Compass

6

7

7

7

7

3

7

4

5

6

5

4

7

6

Fathom

6

7

7

8

7

4

8

7

3

7

7

5

8

5

Fleet

1

1

1

1

1

2

3

3

2

2

2

4

2

2

RGT Planet

3

4

7

3

9

5

4

3

3

6

7

7

8

8

Maritime

2

2

2

2

2

2

3

2

2

2

3

2

2

2

Navigator

7

7

8

7

7

5

6

7

5

8

8

7

8

8

Oxford

3

3

8

4

9

5

3

4

4

6

7

8

9

9

Rosalind

2

2

3

2

4

2

2

2

2

2

3

2

4

3

Spartacus

6

6

7

5

3

4

8

3

3

6

3

3

7

7

Traveller

2

3

7

3

5

6

2

1

2

4

7

7

6

8

Westminster

3

2

5

2

6

4

2

4

2

3

7

5

5

7

IGB1705T

5

4

7

4

3

3

4

2

2

3

3

5

4

4

WI4952

4

4

5

5

4

2

5

2

2

3

2

4

3

6

Leabrook

7

7

5

7

7

5

8

5

5

7

4

5

4

7

Biere

5

4

9

4

7

7

6

4

4

8

5

7

9

7

Charles

8

8

8

7

7

5

7

3

3

4

8

8

7

8

Sunshine

7

6

7

5

8

6

5

4

5

7

7

8

6

8

Table 2. Net form net blotch isolates from SA in 2020 tested on 24 barley varieties. A high number indicates high level of susceptibility.

 SA isolates             
Isolate14/209/2010/2011/2019/2051/2033/2069/2041/2052/2055/2042/2054/2068/20
VarietySpartacusSpartacusBarleyRosalindCompassCompassSpartacusMaritimeCompass?SpartacusSpartacusSpartacusSpartacusCommander
LocationReeves PlainsPt KennyWauralteeMinlatonSouth KilkerranMortanaWarnertownButeNE Pt KennyMt HallMt CooperPt KennyEllistonBeetaloo Valley
Alestar39523738775343
Banks23221224322132
Beast       8746484
Bottler13322326432323
Clipper34432638445243
Commander69744958667496
Compass67732847675374
Fathom79947959776585
Fleet23312249232122
Kiwi13122325232133
Laperouse38533828754252
Leabrook68635838767495
Maritime33323329332232
Maximus56745727545574
RGT Planet34422525445423
Rosalind54622323243232
Schooner46543738-32375
Scope---23327222232
SloopSA25723728434263
Spartacus79864528454474
Traveller34312314333123
Vlamingh24322326433222
Westminster23322736233263
Wl493367643736464354
Biere79973839776386
Figure 1. Incidence of resistance to Systiva (fluxapyroxad) in NFNB samples in 2019.

Figure 1. Incidence of resistance to Systiva (fluxapyroxad) in NFNB samples in 2019.

Wheat powdery mildew

Powdery mildew has become a significant problem in wheat crops on the Northern Yorke Peninsula over the past 3-4 years. The situation has arisen due to growers planting the very susceptible varieties Scepter and Chief CL Plus in close rotation and in neighbouring paddocks. This is reminiscent of the situation on the lower Eyre Peninsula around 2008-2010 when Wyalkatchem was grown intensively in close rotation. In the earlier situation the problem was largely overcome when Mace replaced Wyalkatchem and flutriafol treated fertiliser was widely used. Scepter and Chief CL Plus are similar to Wyalkatchem in their susceptibility to powdery mildew. Unfortunately, this time around the problem has been compounded by the development of resistance to the strobilurin fungicides as well as reduced sensitivity to some of the demethylase inhibitors (DMI) fungicides.

Trials run by Sam Trengrove and supported by SAGIT are investigating the relative efficacy of a range of fungicides around Bute. Their results have shown that flutriafol is providing good early control and should therefore be an effective management option for 2022. Foliar fungicides based on DMI chemistry also provided some good control, but the uneven distribution of disease in paddocks needs to be included in assessing the economic benefits of foliar sprays. It is worth noting that the efficacy of different foliar fungicide treatments is always under-rated where untreated or less effective treatments are included in plot trials since they provide a continuous supply of fresh inoculum that would not occur in a paddock situation. The trial data from Bute showed clearly that the best impact on disease control comes from variety resistance.

Powdery mildew will likely remain a significant problem whilst very susceptible varieties are grown in close rotations. Table 3 provides an indication of which varieties would be more suitable. Varieties rated MSS are much better than those rated SVS.

Table 3. Resistance rating of current wheat varieties to powdery mildew in South Australia.

Ballista

SVS

Catapult

S

Chief CL Plus

SVS

Cutlass

MSS

Grenade CL Plus

MS

Hammer CL Plus

MSS

Mace

MSS

Razor CL Plus

MSS

Rockstar

S

Scepter

SVS

Trojan

S

Vixen

SVS

Wyalkatchem

SVS

Conclusion

The growing of very susceptible varieties as well as the use of close rotations, or no rotation, will often lead to increased disease problems. Reliance on chemical control can be a useful option at times but can also lead to worse outcomes over the longer term not only in individual paddocks but across whole regions for pathogens that have long distance dispersal mechanisms.

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 author would like to thank them for their continued support.

Fran Lopez and Fungicide Resistance team at Curtin University for molecular data to detect resistance mutations.

Useful resources

Cereal Variety Disease Guide 2021

Cereal Seed Treatments 2021

Contact details

Hugh Wallwork
SARDI, Waite Campus
Hartley Grove, Urrbrae SA 5064
0427 001 568
hugh.wallwork@sa.gov.au

Tara Garrard
SARDI, Waite Campus
Hartley Grove, Urrbrae SA 5064
0459 899 321
tara.garrard@sa.gov.au

GRDC Project Code: UOA2003-008RTX, CUR00023,