WA research highlights a need to prepare for barley powdery mildew in 2013
Date: 03 May 2013
- A relatively wet autumn in WA is likely to favour early powdery mildew.
- New research highlights that barley varieties commonly used in WA have increased risk of susceptibility to powdery mildew.
- Fungicide resistance continues to compromise DMI control of powdery mildew in WA.
- Several fungicides are still available to provide effective disease control this year.
- A permit has recently been issued for Group 5 spiroxamine fungicide Prosper® 500 EC – now available as a triazole break early in the season.
- Protective fluquinconazole-based seed dressings can also be effective against early disease.
- Local researchers have updated recommendations to prepare for barley powdery mildew in 2013 - see Table 1 below and DAFWA’s new Fact Sheet: Managing Barley Powdery Mildew in 2013.
- Researchers are interested in any mildew occurring on Oxford and Dash this season and growers are encouraged to send samples to the ACNFP.
||Cultivar resistance rating
||Major resistance genes
|Grange||R-MR||mlo 11|| Durable mlo resistance
|R||mlo 11|| Not required
|Oxford||R||Mlst||Virulence not yet detected in WA||Monitor crops for outbreaks||
|Dash*||R||a7, k1, La||
|Buloke*||MR||La, a7||Virulent pathotypes present in WA but not yet widespread||Monitor crops for outbreaks; Use fungicides in high risk areas||
|Barque*||R||Ga||Virulent pathotypes widespread in WA
|Fleet||MR-MS||Ga||Virulent pathotypes widespread in WA||
|Lockyer||MR-MS||a8, La||Virulent pathotypes widespread in WA||
|Commander||MR-MS||g, Ga + g, La||Virulent pathotypes widespread in WA||
Use seed dressings in mildew prone areas. Foliar applications are likely to be required.
|Bass||MS||a8||Virulent pathotypes widespread in WA||
|Capstan||MS||Ga||Virulent pathotypes widespread in WA||
|Hindmarsh||MS||a8, La||Virulent pathotypes widespread in WA||
|Roe||MS||a8, (He2)||Virulent pathotypes widespread in WA||
|Gairdner||S||g||Virulent pathotypes widespread in WA||
|Hannan||S||a8, (He2)||Virulent pathotypes widespread in WA||
|Mundah||S||a8||Virulent pathotypes widespread in WA||
|Stirling||S||None||Virulent pathotypes widespread in WA||
|Vlamingh||S||a8||Virulent pathotypes widespread in WA||
|Baudin*||VS||a8||Virulent pathotypes widespread in WA||
(Source: Cultivar resistance rating: DAFWA 2013 barley variety guide; resistance gene data: barley breeders and Dreiseitl et al. 2012; status, comments and fungicide recommendations: ACNFP.)
NOTES TO THE TABLE:
(*) Indicates varieties rated MS or better and tested at Curtin University (the status of other cultivars is inferred from pathotype screens on lines containing the resistance genes indicated).
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 2013.
Orange status: Virulent pathotypes of mildew capable of infecting these cultivars are present in WA but were not widespread in 2012.
Red status: Virulent pathotypes of mildew to the resistance genes in these cultivars were widespread in screening in 2012.
Major resistance genes confer protection at the seedling stage as well as adult stages, separate to adult plant resistance by minor genes. Minor genes account for differences in adult resistance ratings where major resistance genes have broken down.
2012 TESTING RESULTS
Resistance ratings research carried out in 2012 by the Australian Centre for Necrotrophic Fungal Pathogens (ACNFP) shows the most commonly used barley varieties in WA are more susceptible to powdery mildew than previously thought.
Researchers from the Centre, an initiative of the GRDC and based at Curtin University, extensively sampled mildew isolates from disease prone regions of WA in 2012.
Major findings included:
- Barley mildew in WA is highly variable.
- New virulent isolates exist.
- Virulence exists against the bulk of major resistance genes in WA barley cultivars, which has seedling disease management implications.
- Resistant varieties, excluding mlo resistance, may become susceptible at some stage in the future.
This is especially significant for varieties currently rated as susceptible (S) to moderately resistant (MR) - including Buloke.
The ACNFP found only Dash and Oxford remain fully resistant, along with newly introduced varieties that contain the durable resistance gene mlo (Grange, Henley, and Westminster) and are awaiting Barley Australia Classification.
The ACNFP confirmed that virulent powdery mildew isolates exist for Buloke and Yagan, but these isolates are not yet widespread.
Centre researchers warn that if 2013 is wet, barley crops should be monitored closely for disease outbreaks – especially Buloke and Yagan.
Table 1 outlines the current status of WA barley varieties to powdery mildew disease, potential virulence threats and seed dressing and foliar fungicide recommendations for 2013.
SUMMARY OF MANAGEMENT OPTIONS FOR POWDERY MILDEW IN 2013:
Choose varieties that are less susceptible to powdery mildew where the disease is a threat.
If 2013 is wet, monitor all barley crops closely for changes in mildew response, particularly those rated Moderately Resistant to Moderately Susceptible.
Avoid using compromised triazoles (DMI) for powdery mildew control. These include tebuconazole, triadimenol, flutriafol, difenconazole (not registered for powdery mildew control) and triadimefon.
Where tebuconazole is present in a mixed product, avoid using it repeatedly.
Avoid using flutriafol-in-furrow – it has variable efficacy and ongoing mutation risk.
Several triazole products are still highly effective - these include fluquinconazole (eg. Jockey® and Stayer), propiconazole, (eg Tilt®), prothioconazole (included in Prosaro®), epoxiconazole (eg. Opus®) and cyproconazole (included in Tilt® Xtra).
Products containing strobilurin are effective – including azoxystrobin (eg. Amistar® Xtra) and pyraclostrobin (eg. Opera®).
A permit has been issued for the use of Prosper® 500 EC, containing the active ingredient spiroxamine, for the control of powdery mildew in barley in WA. It is valid from April 1 2013 to March 31 2016.
Prosper® 500 EC is a Group 5 fungicide, therefore offers an alternative mode of action for control of powdery mildew in barley that will help to extend the life of other fungicides.
The permit states it is to be used at 600mL/ha and applied via boom spray prior to the end of tillering (Zadocks Growth Stage 29) with no more than two applications per crop – seven days apart.
It has a withholding period of 56 days prior to harvest and crops are not to be grazed or fed to livestock for 56 days after application.
Further information about the permit for Prosper® 500 EC can be found at: http://permits.apvma.gov.au/PER14012.PDF
All fungicides, especially strobilurin products, are best used prior to significant disease levels appearing in crops.
Rotate fungicide modes of action and/or active ingredients in a group.Use fungicides as a protectant, rather than as a curative – especially for strobilurin products.
For varieties where major resistance genes have broken down (see Table 1) – and 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® and Maxiflo®.
This is recommended where infection is likely to – or has previously – occurred prior to stem extension.
Do not use triadimenol seed dressing for powdery mildew control.
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.
Manage early nitrogen inputs, potentially splitting a starter application at sowing and a follow-up at stem elongation in high risk areas.
Adequate potassium supplies through fertiliser applications on potassium deficient soils can reduce the affects of powdery mildew.
Grazing crops prior to stem elongation has been shown to help control powdery mildew without affecting crop yield.
Senior Consultant, Cox Inall Communications
042 888 4414
GRDC Barley Powdery Mildew Fact Sheet: www.grdc.com.au/GRDC-FS-BarleyPowderyMildew
ACNFP: Professor Richard Oliver,
The New GRDC Ground Cover magazine supplement Emerging issues with diseases, weeds and pests was included in the January-February 2013 edition of Ground Cover and is available for free download at www.grdc.com.au/GCS102
Details about permit for Prosper® 500 EC: http://permits.apvma.gov.au/PER14012.PDF
Fact Sheet: Managing Barley Powdery Mildew in 2013: http://www.agric.wa.gov.au/objtwr/imported_assets/content/pw/ph/dis/managing_barley_powdery_mildew_in_2013.pdf
Bulletin 4836 – Barley Variety Guide for WA 2013: http://www.agric.wa.gov.au/objtwr/imported_assets/content/fcp/cer/bar/v/bn_wa_barley_variety_guide2013.pdf
Fungicide ratings: NVT website: www.nvtonline.com.au
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