Solutions sought to stop the rot
In the quest to boost rotation profitability, canola has gone beyond a break crop to become an integral staple for the Suckling family at Northampton. During the past five years, GM technology has allowed better weed and herbicide-resistance management during the canola phase and meant that this higher-returning crop could be planted more frequently over wider areas.
This trend has been evident across the high-rainfall areas of the northern wheatbelt and led to a big contraction in lupin and field pea plantings.
But a downside is the cost of managing Sclerotinia, which is the main cause of canola stem rot in this region and can knock 30 to 40 per cent off yields in high-rainfall years.
Karl and Gemma Suckling, who farm with Karl’s parents Eric and Kathy, brother Craig and his wife Trin, say Sclerotinia has been present in their canola crops for at least a decade.
But they say the disease has only started to seriously cut into profits as the oilseed has shifted from being a break crop to a major part of the rotation.
“We have been using Roundup Ready® canola since 2010 and its yield potential is a lot higher than non-GM varieties – so when disease strikes, it has a massive impact,” Karl says.
Sclerotinia survives in the soil for many years and initially infects canola petals, which subsequently drop into the canopy and can lead to leaf and stem lesions, lodging and plant loss.
Canola Sclerotinia surveys undertaken by canola pathologist Dr Ravjit Khangura, from the Department of Agriculture and Food, Western Australia (DAFWA), have found stem infection levels of more than 60 per cent in some paddocks in Sclerotinia-conducive seasons and yield penalties of up to 30 to 40 per cent in the worst-affected crops. This disease has been identified as a major research priority by the GRDC’s Regional Cropping Solutions Networks (RCSN) Geraldton port zone group.
In 2012, the RCSN funded a project led by Geraldton-based Planfarm agronomist Richard Quinlan – carried out in conjunction with DAFWA and local agronomists – to better understand Sclerotinia and its life cycle in the northern wheatbelt.
Although economic control of this disease can be achieved with fungicides (at a cost of about $35 per hectare) the research aimed to find ways to fine-tune control measures. It found Sclerotinia was most damaging in high-biomass crops, which was determined by soil moisture (linked to soil type and landscape position), adequate seasonal rainfall and crop emergence date.
Mr Quinlan says even under very dry conditions, there were crops in the northern wheatbelt in 2012 that lodged in places due to damaging levels of Sclerotinia.
He says this indicates how prolific this disease can be in wetter seasons.
Mr Quinlan says the research showed canola susceptibility to Sclerotinia increased on:
- loam and clay soils that held moisture longer, compared with sandy soils;
- shorter-season varieties that flowered earlier when the disease was sporulating;
- paddocks where there had been reasonable disease levels in previous years; and
- crops that were early sown – leading to high crop biomass early in the season.
Karl says variety trials on his property reflected these results, with early sown and short-season canola varieties losing up to 0.5 tonnes/ha in some years from Sclerotinia when flowering coincided with disease onset. “We would like to grow more of the early season varieties, but it is a high-risk strategy,” he says.
“We will make our variety decision based on yield and then manage Sclerotinia with time of sowing, fungicides and spreading the varieties apart geographically.
“The main problem with this disease is it is expensive to control with fungicides – at up to $60/ha for two applications – and we don’t have a good handle on timing and economic response.
“We also know the disease will hit us every time we have a high-yielding year, because that is when conditions are ideal for its spread.
“The impact will be worst on our best country where canopies are the heaviest and close over quicker.”
This year, the Sucklings have grown about 400ha of the short-season variety 43Y23, 1000ha of the mid-season Hyola® 404 – which has proved to be the best yielding on their property – and 300ha of long-season GT50 to spread their Sclerotinia risk.
Drier-than-average seasonal conditions in mid-winter reduced disease incidence, but fungicides were still needed to control outbreaks across the property.
Karl says he would like to see more research into breeding canola for genetic resistance to Sclerotinia and fungicide timing and application.
Best practice fungicide management is high on the DAFWA plant pathology team’s agenda.
Dr Khangura’s pioneering research work on epidemiology and management of Sclerotinia in the northern agricultural region will provide a strong basis for developing a robust Sclerotinia forecasting system in WA.
This year she has been continuing trials in the northern and southern agricultural regions investigating management of Sclerotinia by optimising timing of fungicide application and crop/canopy density across a range of canola varieties.
Dr Khangura will conduct disease surveys across canola-growing regions of WA to determine the prevalence, disease levels and yield losses instigated by stem rot.
DAFWA Geraldton-based plant pathologist Ciara Beard is also continuing to monitor the spread of Sclerotinia and collect soil temperature, crop canopy humidity and rainfall data from commercial canola crops across the northern wheatbelt.
Mr Quinlan says 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.
He says remotely sensed data from satellite, drones or real-time normalised difference vegetation index (NDVI) sensors might allow growers to measure crop biomass and vary fungicidal applications accordingly.
Karl says this would be a great development for growers and vital for the region as oilseed plantings continue to expand and increase the risk of escalating disease incidence.
0427 839 274,
08 9964 1170,
Dr Ravjit Khangura,
08 9368 3374,
08 9956 8504,
A fact sheet on Managing Sclerotinia stem rot in canola is available at:
A back pocket guide on Diseases of canola and their management is available at:
Managing the risk of Sclerotinia stem rot in canola farmnote 546 is available at:
GRDC Project Code PLN00007, DAW00210