Consultant's Corner: Sclerotinia management - The research view
Author: Natalie Lee | Date: 25 Jun 2014
Western Australian research has shown that applying a single fungicide spray is often effective in reducing canola yield losses from sclerotinia stem rot (Sclerotinia sclerotiorum) when the crop is at the 15 to 30 per cent flowering stage.
But if the sclerotinia pathogen begins releasing spores late in the season, which occurred in WA in 2013, fungicide application has been shown to be effective at the 50 per cent flowering stage.
“The trial results from recent years suggest that the timing of fungicide application should coincide with the onset of spore release but also take into account whether seasonal conditions are likely to be conducive for the development of the disease,” Department of Agriculture and Food (DAFWA) researcher Ravjit Khangura said.
The research led by Dr Khangura, supported by the Grains Research and Development Corporation (GRDC), shows all registered fungicides are effective and that controlling sclerotinia consistently increases crop yields in areas with high disease pressure.
Dr Khangura encouraged canola growers to have foliar fungicides on-hand and ready to apply at the optimum flowering stage, as the ideal spraying window could be as short as a few days.
She said tightening canola rotations in WA and other cropping regions had increased the incidence and severity of diseases such as sclerotinia, posing agronomic challenges to growers.
“This is especially the case in high and medium rainfall zones, where foliar fungicides are becoming a routine part of the canola agronomy package,” Dr Khangura said.
“Yield reductions from this disease can be as high as 30 to 40 per cent – or up to 0.5 to 1 tonnes per ha - in heavily infested crops in high rainfall years.
“Sclerotinia survives in the soil for many years. Spores released from the fungal fruiting bodies initially infect canola petals, which subsequently drop into the canopy and can lead to leaf and stem lesions which cause lodging and plant loss.
“The main management strategy for sclerotinia is to reduce the frequency of host species, in particular broad-leaved crops such as canola, lupins, chickpeas and lentils.
“It is recommended that growers avoid planting canola on paddocks that have had high sclerotinia levels at any time during the previous three years.
“Foliar fungicides (which cost about $30 to $50 per hectare per application) are the only means for in-crop management of sclerotinia.
“Registered fungicides for managing sclerotinia in canola are Prosaro® and products which contain Iprodione (eg. Rovral® Liquid) and Procymidone (eg. Sumisclex® and Fortress®).”
Why sclerotinia was so bad in WA in 2013?
Dr Khangura said sclerotinia was particularly damaging in WA In 2013.
“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,” she said.
Dr Khangura said this was due to five main factors:
- Substantial canola plantings over the last few years resulted in a build-up of sclerotinia inoculum;
- Tight canola rotations have also increased inoculum levels;
- Varietal susceptibility coupled with an extended flowering period;
- Flowering coinciding with spore release from the sclerotinia pathogen;
- Environmental conditions which favoured flower infection and subsequent stem infections.
2013 trials in WA
Research led by Dr Khangura in 2013 built on trials conducted in previous years investigating the optimum time to apply foliar fungicides, to help growers cost-effectively manage sclerotinia.
The 2013 field trial was conducted at East Chapman in WA’s Northern Agricultural Region.
The canola variety Cobbler was sown in a paddock with a history of high levels of sclerotinia.
Prosaro® was applied either as a single application or as two applications at various bloom stages.
Sclerotinia assessments were made two weeks before harvest and all plots were harvested for canola grain yield.
“In the 2013 trial, fungicide applied late in the season at or after 50 per cent bloom significantly reduced the incidence of sclerotinia and significantly improved the canola grain yield compared with the untreated plots,” Dr Khangura said.
“This well timed single spray resulted in a yield increase of 29 per cent and the best gross margin of $102 per hectare.
“Fungicide applied very early at the six to seven leaf stage (before the crop flowered) did not significantly increase yield, and resulted in a negative gross margin.”
“The measured yield loss from sclerotinia in this trial was 26 per cent.”
Dr Khangura said the success of the fungicide applications at or after the 50 per cent bloom stage was possibly due to the later onset of sclerotinia spore release in 2013.
“Trial results from previous, more ‘typical’ seasons, when sclerotinia occurred earlier in the year, showed that fungicide application was most effective at the 15 to 30 per cent flowering stage,” she said.
“In some districts with a history of high levels of sclerotinia and high crop yield potential, two fungicide applications may be cost effective.”
Dr Khangura said late maturing varieties showed the highest levels of sclerotinia in the 2013 trial at East Chapman because the stages of flowering in these varieties coincided with the commencement of spore release.
“However, in a normal season when there is an earlier onset of disease, late maturing varieties may escape serious infection,” she said.
With support from the GRDC, DAFWA is continuing research to refine the use of Prosaro® to control sclerotinia.
Using epidemiological data collected over the last four years, the department is also developing a sclerotinia forecasting system which will help growers make well informed decisions about the use of fungicides, and reduce the requirement for fungicides in seasons unfavourable to sclerotinia like 2010 and 2012.
“In addition, we are working on developing other tools to assist growers in making decisions regarding fungicide sprays and to optimise crop profitability,” Dr Khangura said.
Management practices to reduce risk
Dr Khangura recommends the following management practices to reduce the risk of canola crop damage from sclerotinia:
- Reduce the frequency of host crops – including canola, lupins, chickpeas and lentils;
- Use recommended canola varieties, sowing dates and seeding rates for your district, as the flowering time and length of the flowering period will vary in response to seasonal conditions, and bulkier canopies can favour disease infection;
- Use clean seed free of sclerotes
- Base the use of fungicides on:
- Disease risk
- Conducive conditions for disease development (including rainfall and crop biomass levels)
- Maturity of the variety
- Crop yield potential
- Canola prices
- Foliar fungicides are effective against sclerotinia, but cost about $30-50/ha per application;
- Registered fungicides for managing sclerotinia in canola are Prosaro® and products containing Iprodione (eg. Rovral® Liquid) and Procymidone (eg. Sumisclex®, Fortress®).
- Research has found that in ‘typical’ seasons, a single fungicide application at 15-30 per cent flowering is generally 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.
More information on sclerotinia management is available from the following resources:
GRDC Fact Sheet: Managing Sclerotinia Stem Rot in Canola: www.grdc.com.au/GRDC-FS-Sclerotinia
GRDC Back Pocket Guide: Managing Blackleg and Sclerotinia in Canola: www.grdc.com.au/GRDC-BPG-CanolaDiseases
WA Farmnote 546: Managing the risk of Sclerotinia stem rot in canola: https://www.agric.wa.gov.au/canola/sclerotinia-stem-rot-canola.
Natalie Lee, Cox Inall Communications
08 9864 2034, 0427 189 827
GRDC Project Code DAW00210, DAW00229, UM00051