Plan canola rotations to stop sclerotinia stem rot this season
Author: Melissa Williams | Date: 31 Mar 2014
Tips to minimise Sclerotinia stem rot risk in 2014:
- Clean or grade any retained canola crop seed from last season that shows signs of sclerotia - or use new clean seed.
- Avoid planting canola on paddocks that have had high Sclerotinia levels in the past three years.
- Rotate canola crops and grow break crops such as cereals, field peas and faba beans on high risk paddocks.
- Use recommended canola sowing dates and rates for the district and defer the bulk of nitrogen application to bolting stage - bulky canopies favour Sclerotinia infection.
- Wider row spacings that increase air flow through the canopy may reduce disease levels.
- 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) – as the spraying window can be as short as two days.
Widening canola rotations and using break crops will be integral tools in the management of sclerotinia stem rot this season.
Choosing later maturing canola varieties (agronomically suited to the region) may lessen the impact of this disease if 2014 is a more ‘typical’ year where crop flowering occurs after peak spore release from the fungus Sclerotinia sclerotiorum.
Management practices such as rotation and fungicide use have become more important after widespread incidence of sclerotinia last year has increased inoculum pressure going into this season.
GRDC has released a new fact sheet called ‘Managing Sclerotinia Stem Rot in Canola’ that can be found at: www.grdc.com.au/GRDC-FS-SclerotiniaInCanola.
There are also more tips for dealing with sclerotinia in WA this season in the western pages of the latest GRDC Ground Cover magazine at: www.grdc.com.au/GC109.
Sclerotinia incidence in 2013
Department of Agriculture and Food WA (DAFWA) canola pathologist Dr Ravjit Khangura outlined the vast extent of last season’s sclerotinia stem rot damage at the recent Agribusiness Crop Updates.
She said DAFWA surveys, funded by GRDC, found high sclerotinia incidence across northern and southern canola growing regions - and in some eastern areas.
In the worst affected crops, the disease contributed to yield losses of 0.5-1 tonne/ha.Despite the good season finish, many canola crops in southern areas yielded only 10 per cent more than long term average seasonal yields - partly due to sclerotinia.
This was well below the response from cereal crops, which produced 20-30 per cent higher yields than the long term average.
Plan the rotationThe main control tactic for sclerotinia is to reduce the frequency of host species, such as canola and lupins.
Substantial canola plantings across WA in recent years have led to a build-up of sclerotinia inoculum and tight canola rotations have increased inoculum pressure.
It is now recommended growers avoid planting canola on paddocks that have had high sclerotinia levels during the past three years.
On high risk paddocks, it can be better to use break crops such as cereals (with a canola:wheat:barley rotation), field peas, faba beans or a grass pasture phase – as cape weed and wild radish are also hosts.
DAFWA researcher Jeremy Lemon reports that southern growers observe about 0.3t/ha canola yield improvement in paddocks following pasture where there is a two-year break between canola crops.
He said this also expands weed control options and reduces reliance on particular in-crop herbicides.
Choosing canola varieties
DAFWA trials in 2013 found variety maturity (flowering date) had no effect on sclerotinia incidence last season.
Dr Khangura said this was due to seasonal conditions causing overlapping of flowering time and, consequently, coinciding spore release events with flowering in early and late maturing varieties.
But she said previous DAFWA research in northern areas indicated later maturing varieties can avoid the conditions conducive to sclerotinia infection and record lower levels of disease in a ‘typical’ season because flowering occurs after peak spore release.
She urged growers to use recommended canola varieties, sowing dates and seeding rates for their district, as flowering time and length of flowering period will vary in response to seasonal conditions and bulkier canopies can favour disease infection.
Use and timing of fungicides
Foliar fungicides are effective against sclerotinia, but cost about $30-50/ha per application.
Registered fungicides for managing sclerotinia in canola are Prosaro®, Iprodione-based products (eg. Rovral® Liquid) and Procymidone (eg. Sumisclex®, Fortress®).
Dr Khangura said 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.
Dr Khangura said 2013 trials showed the most effective fungicide control – in a late finishing season - was a late single application of Prosaro® - at a rate of 450mL/ha applied at 50 per cent bloom. This produced yields of 1.2t/ha and a gross margin of $102/ha.
A two-spray strategy using Prosaro® at 10 per cent and 50 per cent bloom led to slightly higher yields of 1.3t/ha, but a lower gross margin of $96/ha.
A very early single spray (6-7 leaf) produced a yield of 1t/ha and a negative gross margin of $13/ha compared to the untreated control.
Previous DAFWA research has found that in more ‘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.
Bayer CropScience technical advisor Rick Horbury said his company’s trials have consistently shown the best and most cost effective foliar application 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.
Although, in canopies with high disease pressure under favourable conditions, he said a second application may be warranted to protect the yield potential of the crop.
A 2013 Bayer CropScience trial in Hyola 404RR near Geraldton found:
- Untreated plots had 53 per cent Sclerotinia disease incidence and yielded 1.2t/ha
- Yields increased by 18 per cent in plots where Prosaro® was used at 375mL/ha at 30 per cent flowering
- Yields increased by 27 per cent where Prosaro® was used at 450mL/ha at 30 per cent flowering.
Yield loss from Sclerotinia
Dr Khangura said preliminary research conducted at two different sites in 2013 to estimate yield loss from sclerotinia indicated that severely affected plants - and plants with lateral branch infections - can lose grain yield of between 92-95 per cent and 18-31 per cent respectively.
Further research in collaboration with NSW Department of Primary Industries (NSWDPI) will help in developing a sclerotinia yield loss model.
Future sclerotinia research efforts
With GRDC support, DAFWA is continuing to monitor the spread, severity and management of sclerotinia across the WA grainbelt in 2014 and beyond.
In conjunction with the NSWDPI, sclerotinia severity maps will be produced annually.
Research has also started into the potential use of biomass/aerial imagery for estimating high disease risk in a timely, useful and cost effective way.
DAFWA’s plant pathology team is in the early stages of developing a robust model for forecasting regional sclerotinia risks and spray decisions.
This is based on Dr Khangura’s pioneering research work on epidemiology and management of sclerotinia during the past five years.
Other research into sclerotinia in WA will focus on: determining yield losses from disease; continuing work into the efficacy and profitability of crop management practices and fungicide use and timing; and an ongoing assessment of spore release, petal infection and stem rot levels to improve epidemiological knowledge.
GRDC Project Codes: DAW00229; UM00051
Ravjit Khangura, DAFWA,
08 9368 3374,
Rick Horbury, Bayer CropScience,
0429 055 154,
GRDC Project Code DAW00229; UM00051