Canola growers on sclerotinia alert

WA canola growers have been advised to take note of risk factors for sclerotinia stem rot and to apply fungicide - within the recommended spray window - if conditions are favourable for infection.

DAFWA researcher Ravjit Khangura said the recent discovery of sclerotinia apothecia (fungal fruiting bodies) in canola paddocks in the Northampton, Geraldton and Moora areas indicated sclerotinia could infect canola crops relatively early this year.

"Seasonal conditions so far, especially in the northern grainbelt, have been conducive to the early production of sclerotinia spores," she said.

"However, the severity of sclerotinia in WA will also depend on coming conditions, with prolonged wet conditions and high humidity in the crop canopy favouring its development."

Dr Khangura said the latest DAFWA research, supported by the Grains Research and Development Corporation, showed that fungicides when applied to canola crops at the 15 to 30 per cent flowering stage were usually most effective in reducing yield losses caused by sclerotinia.

"Some early-sown canola crops in the northern grainbelt are already at this stage of development," she said.

Dr Khangura said the research also showed all registered fungicides were effective, and that if sclerotinia is controlled, increases in crop yield can be achieved where there is high-disease pressure.

"I encourage canola growers to assess their risk and have foliar fungicides on-hand and ready to apply at the optimum flowering stage, as the ideal spraying window can be as short as a few days," she said.

"The crops with the highest risk are those that are sown in paddocks with a history of sclerotinia over the past three years."

Last year, the disease severely damaged canola crops across high and medium rainfall zones of WA, causing an estimated loss of more than $59 million to the State's canola industry.

Dr Khangura said while fungicides reduced crop damage from sclerotinia, the main management strategy was to reduce the frequency of host species - in particular broad-leaf crops such as canola, lupins, chickpeas and lentils.

With support from the GRDC, DAFWA is continuing research to refine the use of fungicides to control sclerotinia, and is developing a forecasting system for the disease.

Northern agronomist Richard Quinlan said his first discoveries of the fungi were made last week, and it was now a waiting game for each variety's flowering threshold percentage and environmental conditions to line up.

Close monitoring of paddocks with previous sclerotinia history will also be undertaken.

"There are a number of farmers in the high rainfall area around the coast that are at risk, definitely … this is the first year we are going to be doing proper, broad-scale spraying," Mr Quinlan said.

"It is up to every specific situation to decide what to do. At this stage I am not recommending spraying anywhere outside the high rainfall, coastal, red loam soil areas that have had a high canola rotation, or considered high risk sclerotinia paddocks."

Mr Quinlan said last year a grower sprayed alternate rows up and down his paddock.

"He showed a 450kg yield increase by applying Prosaro, and that was very late. At about 70 percent flower, it was actually starting to lose some of its yellowness," he said.

"Up until that point we had decided not to spray because it was so dry. That spray went on at about the beginning of August. Even that late it is still part of the overall infection window.

"I also don't want people to get too hysterical about sclerotinia either. It is a high rainfall disease and there are guys out east who would not have a chance at getting their money back."

Defence against the disease is limited to crop rotations, cultural methods and fungicides.

Bayer Crop Science Technical Advisor Rick Horbury said interest in the use of fungicides against sclerotinia had increased and Prosaro 420SC had been in high demand across the State, but warned farmers of the importance of application timing.

"With sclerotinia it's best to be proactive. If the disease is too advanced the damage to your yield potential has been done," he said.

"However, spraying too far ahead of actual infection may mean growers are not getting the best value from their Prosaro application."

Mr Horbury said emerging leaves would not be protected and could leave potential for later crop infection.

"This crop we are looking at today generally presents perfect timing with up to 27 flowers open or unopened, but because the canopy is dry my advice would be to wait until the next rainfall event to apply fungicide," he said.

"Growers should aim to apply Prosaro within the recommended crop stage of 20 to 50 per cent flower, closer to periods of infection risk where leaf wetness and soil moisture are high."