Consider powdery mildew virulence and control when choosing barley varieties in 2014

Key points:

  • Research at Curtin University continues to show barley powdery mildew virulence is highly variable in WA.
  • The majority of commonly used barley varieties have increased risk of susceptibility to this disease.
  • Fungicide resistance compromises DMI control, but several fungicides do provide effective disease control.
  • Protective fluquinconazole-based seed dressings can also be valuable for early disease onset.
  • Monitor any powdery mildew occurring on Dash, Flinders or Oxford in 2014 and send samples to the ACNFP.

Resistance ratings research carried out at Curtin University in 2013 found the majority of barley varieties used in WA remain susceptible to powdery mildew.

With GRDC funding, the university’s Centre for Crop Disease Management (CCDM) research team extensively sampled mildew isolates collected from disease prone regions of WA last season.

Major findings from this work and Department of Agriculture and Food WA (DAFWA) field trials in 2013 included:

  • New virulent isolates for powdery mildew exist.
  • Virulence exists against the bulk of major resistance genes in WA barley varieties and this compromises resistance and affects seedling disease management.
  • Resistant varieties, excluding mlo resistance, may become susceptible at some stage in the future.
  • There are regional differences in variety resistance response.
  • For some barley varieties there are significant differences in the level of disease expression at seedling stage compared with adult stage.

This has ramifications for 2014 barley seed dressing and foliar fungicide recommendations. This is especially significant for varieties currently rated as susceptible (S) to moderately resistant (MR), including Buloke at the seedling stage.

Variety resistance status from 2013 testing

The ACNFP found Dash, Flinders and Oxford remain fully resistant - along with newly introduced varieties that contain the durable resistance gene mlo (Grange and Westminster) and are awaiting Barley Australia Classification.

Testing confirmed that virulent powdery mildew isolates exist for Buloke at the seedling stage and for Yagan, but these isolates are not yet widespread.

Centre researchers warn growers to be vigilant in monitoring barley crops closely for disease outbreaks in 2014 if wet humid conditions that favour mildew occur.

Table 1, below, outlines the latest status of WA barley varieties to powdery mildew disease, potential virulence threats and seed dressing and foliar fungicide recommendations for the coming season.

TABLE 1: Summary of barley powdery mildew status in WA. 

Cultivar

DAFWA seedling resistance rating*

DAFWA adult resistance rating*

Status

Comment**

Fungicide recommendations**

Grange

R

R

Green status

Durable mlo resistance

Not required

Westminster

R

R

Green status

Flinders

R

R

Blue status

Virulence not yet detected in WA

Monitor crops for outbreaks

Oxford

R

R

Blue status

Dash

R

R

Blue status

Buloke

MR

MR

Orange status

Virulent pathotypes present but not yet widespread

Monitor crops for outbreaks. Use seed dressings in mildew prone areas, foliar applications likely to be required for Yagan

Yagan

R

MR-MS

Orange status

Barque

MRMS

RMR

Red status

Virulent pathotypes widespread in WA

Use seed dressings in mildew prone areas. Foliar applications are likely to be required

Lockyer

MRMS

MRMS

Red status

Commander

MRMS

MR

Red status

Bass

MS

MS

Red status

Capstan

MRMS

MRMS

Red status

Hindmarsh

MRMS

MRMS

Red status

Roe

MS

MS

Red status

Gairdner

VS

S

Red status

Hannan

MS

S

Red status

Mundah

S

MSS

Red status

Stirling

VS

S

Red status

Vlamingh

S

S

Red status

Baudin

VS

VS

Red status

NOTES TO THE TABLE:
* 2014 DAFWA resistance ratings provided by Sanjiv Gupta (DAFWA/Murdoch University)
** Comments and fungicide recommendations from the CCDM at Curtin University are based on mildew isolates sampled from across the barley growing regions of WA. Virulent isolates may not be present in some areas, but caution is advised.

Green status: mlo resistance has been robust for years and breakdown is not predicted.
Blue status: Pathotypes of mildew capable of overcoming the major resistance genes in these cultivars have not yet been detected in WA. However, history shows that such genes are easily overcome and monitoring will be carried out in 2014.
Orange status: Virulent pathotypes of mildew capable of infecting these cultivars are present in WA but were not widespread in 2013. Seedling susceptibility was detected in Buloke.
Red status: Virulent pathotypes of mildew to the resistance genes in these cultivars were widespread in 2013.

Differences in seedling and adult responses occur as pathotype-specific major resistance genes confer protection at the seedling stage as well as adult stages. Separate, adult plant resistance genes account for differences in adult resistance ratings where major resistance genes have broken down.

2014 management options for powdery mildew

Varieties

Choose varieties that are less susceptible to powdery mildew where the disease is a threat.

If 2014 is wet, monitor all barley crops closely for changes in mildew response - particularly those rated MR to MS.

 

Effective use of fungicides

Powdery mildew resistance to older triazoles (DMI) is very prevalent in WA.  But newer triazoles and strobilurins provide effective control.


Fungicides tested as being effective by the CCDM are summarised in Table 2 (below).

Table 2: Fungicides for control of powdery mildew. WA status indicates mildew isolates resistant to older triazoles are controlled by the active ingredient(s).


Group

Fungicide Active Ingredient

Product Name Examples

WA Status

Group 3 –DMI

Epoxiconazole

Opus®

OK

Fluquinconazole S

Jockey® Stayer, Maxiflo®

OK

Propiconazole

Tilt®

OK

Propiconazole + Cyproconazole

Tilt®Xtra

OK

Propiconazole + Tebuconazole

Cogito®

OK

Tebuconazole + Prothioconazole

Prosaro®

OK

Group 3+11 – (DMI + Cytb)

Cyproconazole + Azoxystrobin

Amistar Xtra®

OK

Epoxiconazole +

Azoxystrobin

Radial®

OK

Epoxiconazole + Pyraclostrobin

Opera®

OK

Green – OK [Group 3 –DMI]; Dark green – recommended use once a season [Group 3+11 – (DMI + Cytb)]

SApplied as seed dressing.


Growers in coastal and southern regions with a history of mildew should use suitable seed dressings and foliar applications if using cultivars in the red and yellow sections of Table 1.

All fungicides, especially strobilurin products, are best used prior to significant disease levels appearing in crops.

It is important to rotate fungicide modes of action and/or active ingredients in a group and use fungicides as a protectant, rather than as a curative.

Where tebuconazole is present in a mixed product, avoid using it repeatedly. A permit has been issued in WA for the use of the Group 5 spiroxamine fungicide Prosper® 500 EC as a triazole break for powdery mildew early in the season.

It is valid to March 31 2016 and further information is available at: http://permits.apvma.gov.au/PER14012.PDF

Prosper® 500 EC offers an alternative mode of action for control of powdery mildew in barley that will help to extend the life of other fungicides.

Seed dressings

For varieties where seedling resistance has broken down (see Table 1) – especially where rated susceptible in high risk environments - use fluquinconazole-based seed dressings to delay disease onset.

These remain effective and include Jockey® Stayer, CropCare Jockey®, BASF Jockey® and Maxiflo®.

These are recommended where infection is likely to – or has previously – occurred prior to stem extension.


Green bridge

Diseased stubble from the previous season is a major risk factor for powdery mildew infection.

Control the green bridge which may carry inoculum into the next season.

More information:

Simon Ellwood, CCDM
08 9266 9915
srellwood@gmalil.com

Fran Lopez, CCDM
08 9266 3061
fran.lopezruiz@curtin.edu.au

Richard Oliver, CCDM
08 9266 7872
Richard.Oliver@curtin.edu.au

Sanjiv Gupta
08 93323622
s.gupta@murdoch.edu.au

GRDC Project Code CUR00016, CUR00017, DAW00224, DAW00229

Region West