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Barley powdery mildew

  • South Stirlings
  • Dalyup
Powdery mildew on Rosalind barley.
Powdery mildew on Rosalind barley. Photo courtesy of: James Bee (Elders).

James Bee (Elders) has reported finding powdery mildew on early sown Rosalind barley near South Stirlings. The crop had a Uniform® seed dressing and will be sprayed with Aviator Xpro® and monitored for further disease progression.

Powdery mildew is also present in barley at Dalyup.

Powdery mildew has distinctive symptoms. Fluffy, white powdery growths (becoming cream-grey with age) of fungal spores can be seen on leaf surfaces. Under severe pressure later in the season on stems and heads.

Powdery mildew is favoured by mild temperatures (15–22°C) and high humidity (in excess of 70%). Dense crop canopies, high nitrogen nutrition and extended periods of canopy humidity are factors that are understood to favour mildew development. Dry and warm weather conditions that result in periods of low canopy humidity and temperatures above 25°C can reduce disease development.

This finding of powdery mildew is a timely reminder to monitor barley crops, particularly susceptible varieties, for early symptoms of infection. Rosalind barley has an intermediate resistance rating (MRMS) to powdery mildew in its adult stage (after flag emergence), however in recent seasons in southern growing regions (Albany and Esperance port zones) a shift in virulence to the MILa resistance gene means that varieties such as Rosalind are showing a susceptible reaction and need proactive management for powdery mildew. For more variety disease ratings refer to the department's 2021 WA Crop Sowing Guide - Barley.

Barley and wheat powdery mildew are host specific and do not cross infect. However this report indicates that seasonal conditions are conducive for disease development of both and monitoring of wheat and barley crops for powdery mildew (and other diseases) should be ongoing, particularly in areas where pre-season green bridge was apparent.

Seed dressing or in-furrow products applied to manage other diseases may provide some degree of protection from powdery mildew.

Registered foliar fungicides can be used to control powdery mildew infection; application early in epidemic development is most effective. For more information refer to the department’s Registered foliar fungicides for cereals in Western Australia page.

Fungicide resistance

Since 2012 barley powdery mildew in WA has exhibited resistance to some DMI fungicide products and as part of a disease resistance management strategy growers should avoid using ‘compromised’ fungicides.

The compromised triazole ingredients flutriafol, tebuconazole (eg. Orius®), triadimefon (eg. Triadimefon 125 EC), epoxiconazole (eg. Opus®) or propiconazole (eg. Propiconazole 500 EC) will have reduced efficacy, and these are not recommended for powdery mildew control. Any use of these actives indicated above will increase the selection pressure on the fungicide resistant strains of powdery mildew.

One way to reduce the resistance development of the pathogen is to use fungicide mixtures with different modes of action. Thirteen compounds from four modes of action (FRAC Code 3, 5, 7 and 11) are registered in Australia for powdery mildew control (see DPIRD’s Registered foliar fungicides for cereals in Western Australia). Fungicides containing both a strobilurin (Group 11) and an uncompromised triazole (Group 3) active ingredient such as azoxystrobin + cyproconazole (Amistar Xtra®), azoxystrobin + epoxiconazole (Radial®, Tazer Xpert®), azoxystrobin + propiconazole (TopnotchTM), pyraclostrobin + epoxiconazole (Opera®) or succinate dehydrogenase (SDHI; Group 7) base, benzovindiflupyr + propiconazole (Elatus® Ace) or prothioconazole + bixafen (Aviator® Xpro®) should have uncompromised activity against powdery mildew. Use one application per season of each of these strobilurin or SDHI based fungicide mixtures as part of a fungicide resistance management strategy within the disease control program. A powdery mildew specific multisite amine (Group 5), spiroxamine (Prosper 500® EC) is also registered.

For more information refer to DPIRD’s Managing barley powdery mildew in the face of fungicide resistance page.

For greatest efficacy, fungicides should be applied before significant levels of disease establish in crop.

If you suspect fungicide resistance in your paddock then researchers at the Centre for Crop and Disease Management (CCDM) would love to hear from you. To get in touch please email frg@curtin.edu.au or ccdm@curtin.edu.au.

 

For more information on powdery mildew visit DPIRD’s Diagnosing powdery mildew in cereals page and GRDC’s Barley powdery mildew fact sheet.

For more information contact Plant pathologists Kithsiri Jayasena, Albany on +61 (0)8 9892 8477 or Andrea Hills, Esperance on +61 (0)8 9083 1144.

 

 

Article authors: Kithsiri Jayasena (DPIRD Albany), Andrea Hills (DPIRD Esperance) and Geoff Thomas (DPIRD South Perth).