Western Australian grain grower Alex Pearse is among a groundswell of growers now battling wheat powdery mildew – a disease which has become widespread, requires monitoring and attention to detail and, in many cases, has significantly ramped up input costs.
Historically, powdery mildew has occurred sporadically in the WA grainbelt but has not caused significant widespread wheat yield losses in WA for several years.
But the situation was turned on its head in 2015, when it became a major issue in the northern and central wheatbelt - particularly in widely-grown susceptible varieties, such as Wyalkatchem and Corack. A large percentage of popular WA varieties are relatively susceptible to this disease.
Research into the disease has been conducted by the Centre for Crop and Disease Management (CCDM) and Department of Agriculture and Food (DAFWA), with funding from the Grains Research and Development Corporation (GRDC).
This research has shown that powdery mildew infection early in the season can seriously reduce wheat yields – by up to 25 per cent - by reducing photosynthetic leaf area; causing abortion of young tillers; and stunting plant growth.
Infection later in the season, such as between stem elongation and flowering stages, can reduce grain size, lower yields and downgrade quality.
However, 2015 DAFWA field trial results have shown that a single fungicide spray, applied at a registered rate, can reduce the impact of wheat powdery mildew when applied before the disease becomes too severe and before flag leaves and particularly heads are infected.
Timing of fungicide application – as soon as possible after the disease is observed moving up the canopy – has been found to be more important than product choice.
Fungicide application is more likely to be profitable if the outlook is for weather conditions that favour persistence of the disease. Significant yield responses were achieved in four out of six DAFWA trials conducted in 2015. However, two trials showed that a yield response to fungicide application cannot be guaranteed.
In 2016, growers are encouraged to closely monitor early sown, susceptible varieties in particular, to avoid significant damage occurring before management is instigated.
The GRDC and Curtin University are investing $100 million over a five-year period in the CCDM, based at the university, to tackle diseases such as wheat powdery mildew.
Of that funding, about $30 million is a direct investment from GRDC.
For Alex and Cherie Pearse, who farm 4400 hectares in a wheat and lupin rotation, 20 kilometres north of Mingenew, the past three years have seen wheat powdery mildew become a serious annual problem.
This is despite experiencing seasons not typically conducive to wheat powdery mildew,
The disease first emerged on their property in the 1990s, but was controlled by using the fungicide triadimefon and making a variety change from Brookton to Wyalkatchem in 2001.
They introduced mouldboard ploughing to their cropping operation in 2011, but later started to notice powdery mildew developing on freshly mouldboarded areas in low-stubble locations.
“It wasn’t a huge issue, we were always applying fungicide as we went, but in 2013 it became more prevalent,” Mr Pearse said.
“The disease totally went against the rule book in 2014 and 2015.
“We didn’t have the moist conditions, we didn’t have the large biomass, we didn’t have high humidity, we were dry and it was very, very hot, and the powdery mildew just kept growing - even after initial fungicides. We held it but we didn’t actually kill it.”
The Pearse family is looking to change its fungicide program and introduce new wheat varieties beyond Wyalkatchem in a bid to improve control of wheat powdery mildew.
“In 2015, we stepped it up to an $18 per hectare fungicide regime and that seems to be the minimum cost that we’re going to have each year,” Mr Pearse said.
Director of CCDM at Curtin University, Mark Gibberd, said researchers had received a lot of wheat powdery mildew samples from concerned growers and advisors last season.
“Wheat powdery mildew emerged in 2015 as being a major problem for the grains industry in WA,” Professor Gibberd said.
“We know a lot about barley powdery mildew and we know that wheat powdery mildew is very closely related, but the emergence of the pathogen last year took us by surprise.
“Our team, along with DAFWA, have very quickly responded to the situation.
“CCDM researchers are now using new tools which enable us to detect fungicide resistance faster than ever before.
“While we have not seen any signs of fungicide resistance in wheat powdery mildew in WA so far, we have recently picked up the first signs of mutations in NSW and Tasmania which could lead to disease control issues.
“With more time and resources, we will continue to map mutation populations as they appear and keep the industry notified of any further changes.
Professor Gibberd said CCDM researchers were waiting for new wheat powdery mildew samples from the coming season to begin rigorous fungicide testing on isolates to see if there had been a change in pathogenicity which is allowing the pathogen to show a reduced sensitivity to fungicides.
“Pathogens are always evolving and presenting new challenges, and any change in the pathogenicity of powdery mildew of wheat is no different – that’s just the way nature works,” he said,
“The only way we, as an industry, can take action against fungicide resistance is by slowing down the selection of mutations in the population.”
Professor Gibberd said this could only be done by incorporating integrated disease management (IDM) strategies, which is a focus of the CCDM’s Improved Farming Systems Program.
“This program is working with growers and the wider industry to develop and improve IDM strategies that help to delay the development of fungicide resistance, such as looking at stubble management, crop rotations, green bridge and fungicide timing.”
GRDC Grains Research Update papers about wheat powdery mildew and its management are available by following this link and on the CCDM website, which can be accessed by following this link.
To slow down resistance mutations arising in wheat powdery mildew, growers are advised to be mindful of how they use fungicides, and stick to IDM strategies that do not depend solely on fungicides – such as using resistant crop varieties, crop rotations, stubble management and green bridge control.
Natalie Lee, Cox Inall Communications
08 9864 2034, 0427 189 827