Follow good resistance management strategies by applying fungicide before the disease becomes severe, rotating fungicides and not using more than two sprays of any product per season. The article Avoiding a slippery slope in wheat powdery mildew from the Centre for Crop and Disease Management (CCDM) addresses concerns from growers of fungicides not showing complete control in the 2015 wheat powdery mildew epidemic.
To date, there have been no incidences of fungicide resistance in wheat powdery mildew in WA. But the CCDM has recently observed initial genetic changes (or ‘gateway’ mutations) in wheat powdery mildew samples from New South Wales and Tasmania. This could lead to fungicide resistance issues in this disease in Australia.
Poor disease control after fungicide application
Difficulties in controlling the disease observed in the field are unlikely to be the result of fungicide resistance but more likely related to high inoculum pressure, suitability of weather for infection, variety susceptibility, poor canopy penetration, inadequate fungicide rate or use of an outdated product. To avoid development of fungicide resistance follow these recommendations;
- Where possible use fungicide mixtures that contain different modes of action including cyproconazole and azoxystrobin; epoxiconazole and azoxystrobin; and epoxiconazole and pyraclostrobin.
- Spray fungicides at first sight of symptoms if weather conditions are conducive to persistence and control the disease as early as practical.
- Always use recommended fungicide label rates and rotate the fungicide active ingredients that you use - avoid using the same fungicide, or the same mode of action e.g. DeMethylation Inhibitor (DMI) fungicides, application after application.
- Rotate wheat crops with non-host crops such as canola, barley or legumes.
- Keep crops healthy, but avoid over application of nitrogen as that may increase powdery mildew risk.
What to do if you suspect fungicide resistance is occurring in your crop
Contact the Centre for Crop and Disease Management, Fungicide Resistance Group, Curtin University, Perth on +61 (0)8 9266 1204 or firstname.lastname@example.org to request further information and a sample tube so you can submit plant samples. The group is interested in all cases of resistance, including barley net blotches, wheat yellow spot and powdery mildew, botrytis (grey mould), ascochytas in pulses and leptosphaeria (blackleg) in canola.
Over the past few years the DPIRD plant pathology group have been working on many aspects of the biology and management of this disease including variety resistance screening, use of fungicides at seeding or during the season and how variations in the virulence of the pathogen might change variety responses. A Royalties for Regions funded project investigated regional variation in virulence frequencies of WPM and the thresholds in temperature, crop nutrition (nitrogen and potassium) and impact of growth stage on WPM infection and spread, with a focus on management options for growers. The aim of DPIRD's research is to empower growers to be better equipped to fight this disease.
Field work conducted by DPIRD and industry partners in 2015 on foliar fungicide application timing and products is summarised in a 2016 Crop Updates paper available under Documents on the right hand side. We acknowledge gratefully the contribution of trial data from Landmark, Imtrade, Liebe Group and Northampton Agri Services. Previous research done by DPIRD in the 1990s and early 2000s is summarised at Fungicides for Managing Powdery mildew in wheat Historical Trial Report. In 2016, DPIRD investigated the value of seed dressing and in-furrow fungicides for reducing the impact of early powdery mildew in wheat. These research results are available in a 2017 Crop Updates paper available under Documents on the right hand side.
DPIRD gratefully acknowledges GRDC for funding our research, current project is DAW00229 Improving growers surveillance, management, epidemiology knowledge and tools to manage crop disease.
- For latest disease reports subscribe to Pestfax and to report your own disease find please go to Pestfax Map.
- For disease forecasts or outlooks go to Crop disease: forecasts and managment.
- The article Avoiding a slippery slope in wheat powdery mildew in the 25th August 2015 issue of The Spotlight from the Centre for Crop and Disease Management (CCDM).
- A recording of the highly informative webinar Wheat powdery mildew presented by Geoff Thomas (DPIRD) is available on the Training Growers YouTube channel. Growers are encouraged to view this to assist with their decision making on foliar fungicide application.
- GRDC paddock practices article produced in 2016 contains management strategies relevant for any years of high powdery mildew risk.