There is high risk of sclerotinia stem rot, caused by the fungus Sclerotinia sclerotiorum, in parts of that State’s grainbelt in 2017 – especially high rainfall zones.
This is mainly due to conducive conditions for disease last season and potential carry-over from a wetter than average summer.
Growers have been advised to plan ahead and monitor crops as they start to bloom, especially early sown canola that may need earlier fungicide applications if sclerotinia spores are released earlier than usual in the growing season.
Department of Agriculture and Food WA (DAFWA) research officer Ravjit Khangura said sclerotinia stem rot now affects canola crops in most growing areas of WA and, left unchecked, can cause yield losses of 0.5-1 tonnes per hectare. With GRDC investment, she is investigating optimum timing, number and economics of fungicide applications.
She is also researching prerequisite factors for disease forecasting tools and agronomic control measures to help manage this disease.
Key findings from this research to date are outlined in a new GRDC ‘Know More’ video, which can be seen by clicking HERE. It is a short, simple guide to managing sclerotinia stem rot in WA.
CROP SYMPTOMS
Sclerotinia can infect any part of the plant and symptoms appear as bleached, greyish-white or brownish-white fungal growth covering portions of the canola stem. This is sometimes just above soil level, but can occur at any height in the canopy.
When infection is well established, the disease causes plants to wilt and ripen prematurely, resulting in lodging (bending at the stem) and reduced seed production.
Advanced infection will have hard, black and generally irregular-shaped to rounded bodies called sclerotia on the inside of the affected and bleached parts of the stem.
These are the survival structure of the fungus and can be seen when the stem is split open and, occasionally, on outer parts of stem and leaf surfaces if conditions are exceptionally wet and humid.
If the weather is favourable, canola pods may become infected and will appear creamish-white in colour, typically containing white mouldy seeds.
Further information about the disease and diagnosis is available on the DAFWA MyCrop sclerotinia page HERE.
Plant samples can be submitted for definitive diagnosis to DAFWA’s DDLS–Plant Pathology service. For more details click HERE.
BE ALERT TO CONDUCIVE CONDITIONS
High humidity, cool temperatures and prolonged wet weather are ideal for sclerotinia stem rot development, according to Ravjit.
“Seasonal conditions leading up to the seeding period in central and southern grainbelt areas in 2017 have been ideal for early germination of sclerotes that trigger ground-level infections of sclerotinia before crops start flowering,” she said.
“This is a shift away from the more common pathway of primary stem infections that have previously occurred in WA through infected petals. Infection occurring in pre-flowering crops makes fungicide application decisions difficult.”
DAFWA advises that the decision to use fungicides for sclerotinia is best based on:
- Presence of disease symptoms
- Risk of disease – noting previous sclerotinia infections in (or nearby) a paddock and any reports of disease in the area
- Favourable conditions for the development of the disease
- Frequent showers during flowering
- Yield potential/gross margin analysis
MANAGING SCLEROTINIA ON-FARM
Ravjit said best practice management for sclerotinia stem rot included targeted and well-timed fungicide application, coupled with cultural practices such as broader rotations with non-host crops, avoiding sowing in (or near) paddocks with a history of the disease and using clean seed.
FUNGICIDE OPTIONS
Current foliar fungicides registered for sclerotinia are iprodione, procymidone and – more recently – prothioconazole/tebuconazole-based products.
More information about these actives can be found on the Australian Pesticides and Veterinary Medicines Authority (APVMA) PubCRIS database GRDC advises to always check label rates and timing.
TIMING FUNGICIDE APPLICATIONS
Because the source and onset of sclerotinia stem rot each season is variable and unpredictable, researchers in WA are investigating the best times to apply foliar fungicides and collating the results across several years. The aim is to provide better advice for optimal fungicide efficacy for the seasonal conditions that unfold in a particular year.
Based on previous R&D results, DAFWA’s guidelines for optimal timing of fungicide application to help control sclerotinia stem rot include:
- For early disease onset – at 15-30 per cent crop bloom
- For late disease onset/wet spring conditions – at 40-50% bloom
- For average seasons – 20-30% bloom for a single spray (but may require second spray at 40-50% bloom if a wet spring unfolds)
Due to the wetter than average seasonal conditions of 2016, DAFWA trials focused on fungicide application timing to control the secondary spread of ground infections when the disease appeared in the crop.
At a trial site near Moonyoonooka, in the northern agricultural region, the disease level was significantly reduced and canola yields improved with a:
- Single fungicide treatment applied at bloom stages 10, 30 or 50%
- Single fungicide spray three weeks after 50% bloom
- Two-spray treatment at both 10 and 50% bloom
Compared to no fungicides, all treatments (single and two-spray) increased net returns by between $41 and $148 per hectare. This was based on a fungicide cost of $33/ha, application cost of $7/ha and canola price of $550/ha.
At this site, two fungicide applications at 10 and 50% bloom were most effective in reducing disease levels, optimising yields and maximising returns (at a profit of $148/ha).
But even a single application at 50% bloom returned a profit of $118/ha.
Ravjit said it was clear that, although a single fungicide application effectively controlled the disease, two applications provided the maximum benefit, particularly in a prolonged wet season.
She said all fungicides were equally effective for a single or double spray tactic to significantly reduce disease levels, compared to nil treatment.
DAFWA trials at New Norcia, Darkan and Arthur River also found there was good sclerotinia control and higher yields when fungicides were applied soon after noticing the appearance of ground infections to control further spread of the disease.
Trials are continuing this season to further explore the factors driving ground infections and effective control strategies.
ROW SPACING AND PLANT DENSITY
Separate trials were conducted in the northern agricultural region last year to investigate agronomic practices of wider crop row spacing and lower plant density – coupled with fungicide application at 30% bloom. This research found the use of wide row spacing (at 44 centimetres) and/or lower plant density (at 15 plants per square metre), to make conditions less conducive for disease, did not lead to effective sclerotinia control.
Ravjit said there was no difference in disease control between trial plots sown at row spacings of 22cm or 44cm. She said higher targeted plant density (at 30 plants/m2) plots had greater yields than lower plant density plots (at 15 plants/m2), which was consistent with previous research findings.
“The trials demonstrated that wider row spacing and/or lower plant densities alone will not provide advantages in sclerotinia control in some seasons,” she said.
BREEDING FOR DISEASE RESISTANCE
GRDC is investing in pre-breeding sclerotinia resistance research at the Curtin University-based Centre for Crop and Disease Management (CCDM).
In 2016 and 2017 this project is phenotyping 100 spring canola varieties for resistance and screening for resistance in varieties when infection enters the plant from the ground.
Data will feed into GRDC’s national canola breeding program.
More information:
Ravjit Khangura, DAFWA
08 9386 3333
ravjit.khangura@agric.wa.gov.au
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