Management strategies to help control sclerotinia stem rot in 2015:
- Clean or grade any retained canola crop seed from last season showing signs of Sclerotinia sclerotiorum (or sclerotia) fungus - or use new clean seed
- Avoid planting canola on or near paddocks that have had high sclerotinia levels in the past three years
- Use non-host break crops, such as cereals, field peas and faba beans, on high risk paddocks
- Use recommended canola sowing dates and rates for the district
- Have foliar fungicides on-hand and ready to apply at optimum flowering stage (20-30 per cent flowering or 50 per cent flowering when epidemics are late)
Caption: Keep a watch for sclerotinia this season, as Sclerotinia sclerotiorum (or sclerotia) fungus from seasons 2013 and 2014 will have survived in the soil. Photo: DAFWA.
Regional risks for sclerotinia stem rot incidence and severity across WA and decisions about whether and when to use foliar fungicides in season 2015 will depend on a range of factors.
Latest information stemming from GRDC-funded pioneering epidemiology and disease management research work carried out by the Department of Agriculture and Food (DAFWA) show these risks are based on:
- Crop rotation history
- Disease incidence in the last affected crop
- Distance from 2014 affected crops
- Weather factors leading up to the production of apothecia
- Percentage of petal infection
- Conditions favourable for stem infection.
Led by canola pathologist Dr Ravjit Khangura, with GRDC funding, DAFWA researchers will continue to monitor the spread, severity and management of sclerotinia across the WA grainbelt as season 2015 unfolds.
The focus is on: determining yield losses from disease; the efficacy and profitability of crop management practices; fungicide use and timing; and an ongoing assessment of spore release, petal infection and stem rot levels to improve epidemiological knowledge.
Sclerotinia risk for WA crops in 2015
Sclerotinia incidence was widespread across WA in 2014, but less favourable conditions after flowering in many areas of the State confined economic losses to about $23 million.
That was less than half of the estimated $59 million worth of production lost in 2013, when the worst affected regions reported crop yield reductions of 0.5-1 tonnes/hectare.
Bayer CropScience technical adviser north, Rick Horbury, told the recent West Midlands Group GRDC-DAFWA Regional Crop Update meeting that of concern for 2015 is that Sclerotinia sclerotiorum (or sclerotia) fungus from seasons 2013 and 2014 will have survived in the soil.
Each sclerotia can produce up to 15 mushroom-like apothecia that release millions of spores to infect leaves and petals if conditions are right during the growing season.
In the northern agricultural region last year, apothecia - after initial emergence from the soil - started releasing spores and there was infection observed on crop leaves within 10 days.
About three weeks after apothecia emergence, with wet and humid conditions, the disease progresses, there is an increase in petal infection and then stem infection and rot occurs.
Rick says early apothecia emergence, before significant leaf infection, is decision-making time and (in his experience during the past three seasons) crop yields will drop by about 0.5 per cent per hectare for every 1 per cent of crop infected (across all canola varieties).
Triggers for sclerotinia development and fungicide decision-making
- Temperatures of 10-15°C in the soil suit sclerotia-producing, mushroom-like apothecia
- More than 40mm of rain and 75 per cent humidity in the three week period before and after early canola bloom can kick-start spore release from apothecia and petal infestation
- In WA, experience has shown 25mm of rain after initial flowering is enough to start spore release and infection in northern regions
- About 18-36 hours of continual leaf wetness is essential for initiation of infection events
- Air temperature does not seem to be a limiting factor for spore release and stem infection development in WA
- In the northern agricultural region in 2014, disease severity increased when wet spring conditions returned - despite a long dry spell in winter and maximum air temperatures above 30°C for a few days.
Deciding whether and when to spray
Dr Khangura says if there is a wet start to the season and spore production occurs - but then conditions become drier at the time of flowering - there may be no need to apply fungicides.
But fungicides may be needed if wet and humid conditions prevail, especially at time of flowering.
If the forecast is for dry conditions at a particular bloom stage, there may be no need to do a second treatment.
Rick has devised a ‘watch and act’ scenario planner for sclerotinia development and fungicide planning in WA - based on levels of risk – and presented this to the West Midlands Group Update meeting (See Table below).
He says if a property starts climbing from low risk to adjacent or high risk, it is time to budget for some fungicide application – and late sprays can be economic under disease-conducive conditions.
Table: Sclerotinia evolution in WA, stages of disease frequency and pressure. Source: Rick Horbury, Bayer CropScience technical adviser north.
Foliar fungicides are effective against sclerotinia, but cost about $25-50/ha per application.
Registered fungicides for managing sclerotinia in canola can be found on the Australian Pesticides and Veterinary Medicines Authority (APVMA) PubCRIS database and smartphone application.
These include products based on the actives iprodione or procymidone or the mixture of actives prothioconazole + tebuconazole (Prosaro®).
Dr Khangura says use of fungicides will be determined by:
- Inoculum presence
- Conducive conditions for disease development (including rainfall and crop biomass levels)
- Crop growth stage
Crop yield potential
- Canola prices.
Previous DAFWA research has found that in ‘typical’ seasons, a single fungicide application at 20-30 per cent flowering is often effective in reducing yield losses from sclerotinia by preventing main stem infections.
In some districts with a history of high levels of stem rot and high crop yield potential, a second application may be cost effective if weather conditions continue to remain favourable for disease development.
Dr Ravjit Khangura, DAFWA
08 9368 3374
Rick Horbury, Bayer CropScience
0429 055 154
Melissa Williams, Cox Inall Communications
042 888 4414
GRDC Project Code