Australia
August 13, 2013
Source: GRDC
Evidence of sclerotinia in canola is starting to emerge in the northern wheatbelt on the back of recent cooler moist conditions and the closing over of crop canopies.
The window for effective preventative fungicide control of this disease in the region has closed for the bulk of crops - or is rapidly closing - and it is advisable to monitor canola closely for signs of infection.
That is the advice from Planfarm agronomist Richard Quinlan, who led a GRDC-funded research project in 2012 to better understand sclerotinia and its lifecycle in canola in the northern agricultural region.
Although economic control of this disease can be achieved with fungicides - at a cost of about $35/ha - this research aimed to find ways to fine-tune control methods.
The project was initiated by the GRDC’s Regional Cropping Solutions Networks (RCSN) Geraldton port zone group, which has identified profitable rotation crops and sclerotinia as priority issues in the region.
ABOUT SCLEROTINIA
Sclerotinia sclerotiorum is considered the main cause of canola stem rot in the northern high rainfall zone.
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.
These germinate after prolonged soil moisture - usually after the crop canopy has closed and the soil surface is permanently shaded.
They form small mushroom-shaped, cream coloured fruiting bodies - called apothecia - that spread disease ascospores.
Ascospores initially infect canola petals, which lodge in the canopy and cause a lesion on leaves and stems.
Infected stems become weak at the lesion site and this can cause lodging and plant loss.
Sclerotia form in the infected stems and are then spread around the paddock into the soil at harvest time.
Without good harvest hygiene, these sclerotia can remain in any retained seed and be re-sown into other paddocks the following season – further spreading disease.
MONITOR IN HIGH RISK AREAS
Field observations indicate sclerotinia is the worst canola disease on loam and clay soils in the northern wheatbelt and is often more yield-limiting than Blackleg.
Known hot spots for this disease are coastal areas around Northampton, pockets of Chapman Valley, Walkaway, Rudds Gully and the Greenough flats.
Sclerotinia is also becoming an increasing problem for growers in the Esperance region.
Apothecia were found in late July this year at Narngulu, nearby Georgina (near Walkaway) and north west of Northampton two weeks after a 30mm rainfall event on July 8 that followed a six-week dry spell.
This is thought to be the start of the full disease cycle in the northern wheatbelt – a month later than experienced in previous years that had more June rainfall.
About two months after canola has been sown, when conditions are cool and moist and the crop canopy has started closing over, look for signs of:
- Apothecia: mushroom shaped, cream colour, about 3-5mm in diameter and found at the base of plants.
- A few weeks later – whether you have seen apothecia or not – check for leaf lesions that have a watermark appearance or white broken patches.
- Leaf lesions are being seen at present at many known disease hotspots.
- Leaves that are broken/bent at a lesion and growing white fluffy fungal growth.
- Stem rotting or stem lesions (initially appearing as a white bleached oval) – these are being seen at present in some Esperance crops.
- Large patches of lodged crop from broken rotting stems.
- Advanced infection: hard, black, generally irregular-shaped sclerotia on the inside of the affected and bleached parts of the stem.
- Stems can be carefully split to observe the black sclerotia within.
At one site in the 2012 RCSN research trials, sclerotinia apothecia survived for about one month - providing some indication of the period of disease spread at this time of the year.
IMPACT OF SCLEROTINIA
Canola sclerotinia surveys undertaken by the Department of Agriculture and Food WA’s canola pathologist, Ravjit Khangura, in canola growing regions of WA during the past five years have revealed stem infection levels of above 60% in some paddocks in sclerotinia-conducive seasons and yield penalties estimated at up to 30-40% in worst affected crops.
Vigilant monitoring of canola crops is required to minimise potential yield loss.
The 2012 RCSN research project – carried out in conjunction with DAFWA plant pathologist Ciara Beard and other local agronomists – showed that even under very dry conditions, there were crops in the northern wheatbelt that lodged in places due to damaging levels of sclerotinia.
This indicates how prolific this disease can be in wetter seasons in the region.
The research showed canola susceptibility to sclerotinia increased:
- On loam and clay soils that hold moisture longer compared to sandy soils.
- On leafier varieties that have good canopy cover.
- In paddocks where there had been reasonable disease levels in previous years.
- If crops were early sown - leading to high crop biomass early in the season.
Sclerotinia was found to be most damaging in high biomass crops, determined by:
- Soil moisture (which is linked to soil type and landscape position).
- Adequate seasonal rainfall.
- Crop emergence date.
Richard says crop biomass 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 NDVI sensors might allow growers to measure crop biomass and vary fungicidal applications accordingly.
LATE SEASON FUNGICIDE OPTIONS
Currently registered fungicides for management of sclerotinia in canola include Prosaro®, Iprodione (eg. Rovral® Liquid) and Procymidone (eg. Sumisclex®, Fortress®).
Spraying is recommended when the canola is between 20 and 50% flowering – refer to product label, as products differ.
Bayer CropScience technical advisor Rick Horbury says Prosaro® 420 SC is registered for sclerotinia control in canola crops this season from 20 per cent to 50 per cent flowering (full bloom) stage.
The company’s trials have consistently shown the best and most cost effective foliar spray timing for Prosaro® 420 SC is a single spray at full label rates (it is registered for use at 375-450 mL/ha) at 20-30 per cent flowering.
Late applications at 40-50 per cent flowering can result in reduced canopy penetration and inefficient control under high disease pressure.
Rick is conducting trials in the northern wheatbelt this season to assess effectiveness and timing of two spray strategies for sclerotinia control on a range of hybrid varieties.
DAFWA trials in the 2011 season found Prosaro® at 525mL/ha applied in a single application at 10-15% flowering significantly reduced sclerotinia incidence and improved seed yield compared to nil and Rovral® treatments at 2litres/ha.
But Ravjit suggests many northern crops have now passed this fungicide window and it may be uneconomic to conduct a late application that may not provide highly effective disease control.
The economic benefits of spraying will depend on yield potential, disease level, weather forecasting systems and canola prices.
The seasonal conditions during the 2011 trials were ideal for disease development and high yield potential of the crop, so the result will differ for a ‘normal season’ with moderate disease levels.
FUTURE RESEARCH
DAFWA’s Ciara Beard is monitoring the spread of sclerotinia disease and its development in commercial northern wheatbelt canola crops this season and collecting soil temperature, crop canopy humidity and rainfall data from a range of sites.
She says DAFWA is considering the use of biomass/aerial imagery to assess if this could help with estimates of high disease risk in a timely, useful and cost effective way.
Ciara says her data and observations from this season will be used by DAFWA’s plant pathology team, which is in the early stages of developing a model for forecasting sclerotinia risk and incidence in canola and economic control thresholds.
Ravjit’s pioneering research work on epidemiology and management of sclerotinia in the northern agricultural region during the past four years will provide a strong basis for developing a robust sclerotinia forecasting system in WA.
This year she is continuing trials in the northern and southern agricultural region investigating management of sclerotinia by optimising timing of fungicide application and crop/canopy density across a range of canola varieties.
RCSN INITIATIVE
RCSN groups are set up by the GRDC in all port zones to help fast-track the time it takes for new varieties, practices and technologies to be adopted by growers - ultimately increasing the profitability of the Australian grains industry.
RCSN members include a GRDC western panellist, farmers, and representatives from agribusiness and research and development organisations and a big part of their role is determining regional research priorities.
GRDC Project code: PLN00007
More Information:
Richard Quinlan, Planfarm, 08 9964 1170, rquinlan@planfarm.com.au
Ciara Beard, DAFWA, 08 9956 8504, Ciara.beard@agric.wa.gov.au
Ravjit Khangura, DAFWA, 08 9368 3374, Ravjit.khangura@agric.wa.gov.au
Rick Horbury, Bayer CropScience, 0429 055 154, rick.horbury@bayer.com
Sally Thompson, RCSN, 0417 983 356, sowingseeds@bigpond.com
Useful resources:
GRDC Fact Sheet: Managing Sclerotinia Stem Rot in Canola: www.grdc.com.au/GRDC-FS-ManagingSclerotiniaStemRotInCanola
GRDC Back Pocket Guide: Managing Blackleg and Sclerotinia in Canola: www.grdc.com.au/GRDC-BPG-ManagingBlacklegAndSclerotiniaInCanola
More information about the GRDC RCSN network: www.grdc.com.au/rcsn, or contact Cameron Weeks: 0427 006 944 (Geraldton port zone).
Disclaimer
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CAUTION: RESEARCH ON UNREGISTERED PESTICIDE USE
Any research with unregistered pesticides or of unregistered products reported in this document does not constitute a recommendation for that particular use by the authors or the
authors’ organisations.
All pesticide applications must accord with the currently registered label for that particular pesticide, crop, pest and region.
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