Take steps to stop sclerotinia rot in canola this season

Author: Melissa Williams | Date: 07 Jan 2014

Key points

  • Sclerotinia sclerotiorum is one of the main causes of canola stem rot in high rainfall areas across southern Australia.
  • Its impact is considered to be worse on loam and clay soils in WA, where it is often more yield-limiting than Blackleg.
  • National canola Sclerotinia surveys have found stem infection levels above 60 per cent in some paddocks in conducive seasons.
  • Yield penalties can be as high as 30-40 per cent in the worst affected crops.
  • Economic control can be achieved with fungicides at a cost of about $30-$50/ha.
  • GRDC-funded research aims to better understand the Sclerotinia lifecycle and fine-tune disease management tactics.

Tips for minimising sclerotinia disease risk in 2014

  • Clean or grade any retained canola crop seed from last season that shows signs of sclerotia, or use new clean seed.
  • Avoid planting canola on paddocks that have had high Sclerotinia levels during the past three years.
  • Rotate canola crops and grow break crops such as cereals, field peas and faba beans on high risk paddocks.
  • Use recommended canola sowing dates and rates for the district – bulky canopies favour Sclerotinia infection.
  • Consider wider row spacings that will increase air flow through the canopy until it closes over.
  • Have foliar fungicides on-hand and ready to apply at the 20-30% flowering stage – as the spraying window can be as short as two days.

NSW DPI plant pathologist Kurt Lindbeck inspects canola in the greenhouse as part of Sclerotinia incidence and control research. PHOTO: Deanna Lush

Stem rot caused by Sclerotinia sclerotiorum was highly damaging in canola crops across many high and medium rainfall areas of southern Australia that received regular spring rainfall in 2013

This has prompted a warning about careful disease management this year to minimise risks of production losses.

Sclerotinia is emerging as a serious threat to production across all major canola growing regions of Western Australia, where rainfall events can coincide with flowering and lead to widespread stem rot development.

Sclerotinia is also estimated to have infested up to 60 per cent of individual canola crops in parts of southern NSW, Victoria and South Australia during 2013 on the back of seasonal conditions that were perfect for disease development.

Heavily infested crops can suffer yield losses of 30-40 per cent in high rainfall years and costs to control this disease with fungicides are about $30-$50 per hectare per application.

Sclerotinia has been identified as a major research priority by the Grains Research and Development Corporation (GRDC) and its Regional Cropping Solutions Networks (RCSN) in affected port zones.

ABOUT SCLEROTINIA

Sclerotinia sclerotiorum is the main cause of canola stem rot in high and medium rainfall zones of southern Australia.

Sclerotinia minor may also be present, but is thought to be less significant.

Sclerotinia sclerotiorum survives in the soil for many years as sclerotia - which are hard, dark resting bodies of the fungus and may look like mouse droppings.

These germinate after periods of prolonged soil moisture (one to two weeks), usually after the crop canopy has closed and the soil surface is permanently shaded.

They form small (5mm in diameter) golf-tee shaped, cream-pale brown coloured fruiting bodies - called apothecia - that release airborne ascospores.

Ascospores initially infect canola petals, which later lodge in the crop canopy and cause lesions on leaves and stems.

Infected stems initially show a white lesion that spreads and can appear as fluffy white growth.
The stem becomes weak at the lesion site - halting transfer of nutrients to the canopy – and this can cause lodging and plant loss.

Sclerotia form within the infected stems and are then spread around the paddock and into the soil at harvest time, where they can remain for up to 10 years.

Without good harvest hygiene and seed cleaning, these sclerotia can also remain in any retained seed and be re-sown into other paddocks in the subsequent season – further spreading disease.

DISEASE INCIDENCE

Sclerotinia was widespread across WA’s northern and southern wheatbelt in 2013 and has become the worst disease affecting canola in those parts of the State - often more yield-limiting than Blackleg.

It is also becoming an increasing problem for growers in the Esperance region on the State’s south coast.

Sclerotinia surveys have been carried out across WA’s canola growing regions during the past five years by Department of Agriculture and Food Western Australia (DAFWA) canola pathologist Dr Ravjit Khangura.

She has found stem infection levels of more than 60 per cent in some paddocks in conducive seasons and yield penalties of up to 30-40 per cent in the worst affected crops.

In parts of NSW, Victoria and SA a ‘perfect storm’ of factors led to widespread and damaging levels of Sclerotinia during the 2013 season.
NSW Department of Primary Industries plant pathologist, Dr Kurt Lindbeck, said winter conditions favoured petal infection and disease development.
He said frequent spring rainfall and early canola flowering – by three to four weeks - further encouraged the disease.
“With the right environmental conditions, as we witnessed last year, it doesn’t take much for disease outbreaks to occur,” he said.

FORECASTING SCLEROTINIA

GRDC and DAFWA are investing in pioneering Sclerotinia epidemiology and management research in WA to better understand the Sclerotinia disease lifecycle.

The aim is to develop a robust disease risk forecasting system and determine optimal timing for fungicide applications.
A 2012 project led by Geraldton-based Planfarm agronomist Richard Quinlan, carried out in conjunction with DAFWA and local agronomists, showed Sclerotinia was most damaging in canola crops with high biomass early in the season.

Biomass levels were driven by soil moisture (linked to soil type and landscape position), adequate season rainfall and crop emergence date.

Mr Quinlan said crop biomass could potentially become a critical measure of conditions for Sclerotinia infection and a tool to help determine when fungicide control would be timely, accurate and cost effective.

In the eastern states, GRDC-funded research into Sclerotinia is focusing on developing a better understanding of the conditions that lead to a Sclerotinia stem rot outbreak.

Dr Lindbeck said this included identification of high disease risk districts so that in future, warnings of disease outbreaks could be more targeted.
He said researchers were also working with DAFWA in the development of a disease risk forecasting system that could be used in the eastern states.

VARIETIES AND ROTATIONS

Dr Khangura said genetic resistance to Sclerotinia in commercial canola varieties was very small or unknown.

She said variety time of flowering might have some influence on the incidence and severity of disease.
“DAFWA trials have indicated that in a ‘normal’ growing season, later maturing canola varieties can often escape Sclerotinia damage - as they flower after peak spore release,” she said.

“But in 2013, mid and late-maturing varieties were badly affected in the northern region of WA due to high frequency of spring rain events that provided conducive conditions for spore release and disease development.”

Dr Khangura said rotation planning was an increasingly important tool to manage Sclerotinia in susceptible areas.
“Tight cereal-canola rotations will lead to high disease levels in conducive seasons,” she said.

“Cereals and non-broadleaf crops are ideal break crops.”
Dr Khangura also recommended Sclerotinia be controlled in pasture and broadleaf legume break crops to help halt the disease cycle.

In eastern Australia, tight wheat-canola rotations are contributing to increased incidence of Sclerotinia.

Dr Lindbeck said the frequency of canola every second year was doing a great job of maintaining high levels of viable sclerotia in the soil.
“Often wheat-canola rotations are used in higher yielding districts, where the disease most frequently occurs,” he said.

SCLEROTINIA AND FUNGICIDES

Currently registered fungicides for management of Sclerotinia in canola are Prosaro®, Iprodione (eg. Rovral® Liquid) and Procymidone (eg. Sumisclex®, Fortress®).

The total cost of treatment, including product and application, varies but ranges from about $30-$50/ha. A single fungicide application at 20-30 per cent flowering is often effective in reducing yield losses from stem rot by preventing main stem infections, according to Dr Lindbeck.

“In some districts with a well known history of high levels of stem rot and high crop yield potential, a second application may be cost effective,” he said.

“The aim is to prevent early infection of petals and ensure the fungicide also penetrates into the lower crop canopy to protect potential infection sites – including leaf axils and lower stems.”

Dr Khangura said use of fungicides would be determined by presence of disease, conducive conditions for disease development – including rainfall and crop biomass levels – maturity of variety, crop yield potential and canola prices.

She said DAFWA trials had shown all registered fungicides were effective and fungicide use had consistently increased crop yields in areas with high disease pressure, compared to nil treatments.

Trials in the 2011 season found where single fungicide applications were used at 10-15 per cent flowering, returns were $79 to $200/ha higher (depending on product) than for untreated plots.

Using two fungicide applications at 10-15 per cent and again at 40 per cent flowering in these trials increased returns by $40 to $240/ha (depending on product), compared to untreated plots.

Bayer CropScience technical advisor Rick Horbury said his company’s trials had consistently shown the best and most cost effective foliar spray timing for Prosaro® 420 SC was a single spray at full label rates (it is registered for use at 375-450 mL/ha) at 20-30 per cent flowering.

But he said trial work had recorded improved yields from multiple spray applications under high disease pressure.

In a 2013 Bayer CropScience trial, Prosaro was applied at 30 per cent flowering in Hyola 404RR near Geraldton in WA’s northern wheatbelt.

Mr Horbury said untreated ‘control’ plots recorded Sclerotinia disease incidence of 53 per cent and yielded 1.2t/ha. He said Prosaro used at 375mL/ha resulted in 18 per cent higher yields than the control plots and Prosaro used at 450mL/ha increased yields by 27 per cent.

Mr Horbury said single late fungicide applications at 40-50 per cent flowering could result in reduced canopy penetration – particularly when there is high disease pressure.

“With a disease like Sclerotinia, it is better to be proactive as it is a bit like a snowball rolling down a hill - once it gets momentum it is difficult to stop,” he said.

In the 2013 season, where there was late spring infection, good economic returns were recorded for applications at 40-50 per cent flowering in the central midlands and Great Southern areas of WA.

“The most important factor for achieving consistent economic returns from a foliar fungicide treatment is that its timing coincides with conditions conducive to Sclerotinia infection,” Mr Horbury said.

Dr Khangura is studying fungicide application timing and to date her trials have found early applications are the most effective in reducing disease impact and increasing yields.

“But this disease is highly weather sensitive and the crop response will change each year, depending on how the season unfolds – particularly in relation to spring rainfall and timing of spore release,” she said.

WHAT THE FUTURE HOLDS

Crop biomass imagery could be a potential future measure of conditions for Sclerotinia infection and a tool to help determine when fungicide control would be timely, accurate and cost effective.

Remotely sensed data from satellite, drones or real time NDVI sensors might allow growers to measure crop biomass and vary fungicidal applications accordingly.

This could be a vital development for growers as oilseed plantings continue to expand and increase the risk of escalating disease incidence.

In the immediate term, DAFWA will continue to monitor the spread of Sclerotinia disease (including apothecia development) in 2014 and collect soil temperature, crop canopy humidity and rainfall data from a range of sites.

This information is being used by its plant pathology team to develop a model for forecasting Sclerotinia risk and incidence in canola and economic control thresholds.
Nationally, research in 2014 will centre on improving the understanding of the critical ‘trigger points’ that lead to a Sclerotinia stem rot outbreak.

This includes monitoring spore release, petal infection and development of stem rot.

Research will also continue to determine disease level and yield loss thresholds to improve decision-making about application of fungicides and the interaction between flowering period and foliar fungicide application.

ENDS

GRDC Project Code UM00051; DAN177; PLN00007

Region West, North, South