Conditions in Western Australia during the 2018 growing season were favourable for the development of sclerotinia in canola crops. Sclerotinia apothecia were first observed mid-July in Geraldton and persisted until September in many places. Infection in canola was detected as early as August with the first report being received in a crop at Northampton. The dry spring in many areas hindered disease progress in most areas, but there are likely to be significant levels of disease inoculum (sclerotia) left behind in some paddocks after harvest.
Sclerotia of sclerotinia can survive in the soil posing a serious risk of infection to susceptible crops sown in the infested paddocks.
The most common infection pathways in WA are via infected petals and airborne spores. However, basal or pre-flowering infections were observed in some canola crops in 2018, particularly under very wet conditions in paddocks that have high inoculum levels. Regular rainfall events in 2018 were conducive to basal infection, which is believed to be caused by hyphal or myceliogenic germination of sclerotia on or below the soil surface; infecting the base of plants causing fluffy, white growth and lesion development on the stem at ground level or on lower leaves before flowering has commenced. The Department of Primary Industries & Regional Development (DPIRD), NSW Department of Primary Industries (NSW DPI) and the Centre for Crop Disease Management (CCDM) are conducting research into how this occurs, but it appears to be a separate infection avenue to the regular sclerotinia infection that occurs after crop flowering has commenced.
Planning for sowing in 2019
- Rotate canola with non-host crops (for example, cereals) and use clean seed (free of sclerotia).
- Sclerotinia stem rot in lupins and other pulses is caused by the same fungus (Sclerotinia sclerotiorum) that infects canola. It can infect most broadleaf crop and pasture species but not cereals. So lupins and other broadleaf crops are not a break crop for the disease.
- In previously infected canola crops and nearby paddocks, growers are advised to sow non-host crops in 2019 and use clean canola seed (not contaminated with sclerotia).
What about burying sclerotia?
Mouldboard ploughing of infected stubble may reduce carryover to subsequent crops as deep burial, greater than 15cm, limits germination of sclerotia and the development of apothecia. Most sclerotia germinate if they are close (within 2-3cm) to the soil surface but may survive for five or more years when buried at greater depths. However, deep burial is only effective if deep tillage is not used in the following years to ensure that sclerotia are not brought back to the soil surface. Hence, management with tillage is uncertain.
Does grinding sclerotia work?
Research conducted by DPIRD has shown that by finely grinding sclerotia, such as with a weed seed destructor, their germinability and persistence can be reduced, but not eliminated.
In-season management options
The following in-season sclerotinia management options are recommended:
- Applying a single foliar fungicide application at 30-50% bloom (Fig 1). Please see below the bloom stages in canola, and information on the new SclerotiniaCM app for assistance with spray timing decisions.
- Two fungicide applications are only beneficial in an extended wet season when disease risk remains high into spring and the crop has high yield potential.
- Late spray applications (after 50% bloom) are generally not economical, and can not be recommended as these applications can create a withholding period concern. It is important to follow fungicide label instructions.
- Currently it is unknown if applying a foliar fungicide for basal infection prior to flowering is effective but it will protect the upper canopy from new infections. The fungicide needs to be applied at or before 30% bloom. Fungicide application for blackleg timing does not work for controlling sclerotinia.
- Fungicide application is still warranted in crops with wide row spacing (44 cm) if the seasonal conditions (high rainfall and humidity) become favourable during flowering.
- Only use registered foliar fungicides to manage sclerotinia.
A new, free tablet-based app to assist canola growers across Australia to better manage the canola disease, Sclerotinia stem rot, was launched in February this year. This app is designed to assist canola growers to make more informed decisions about fungicide applications to optimise yields and minimise costs. SclerotiniaCM can be used during the growing season to assist crucial treatment decisions using evidence-based information to estimate the likely returns from spraying for Sclerotinia for individual paddock scenarios.
- Further information on DPIRD’s research on finely grinding sclerotia can be found in the 2018 Grains Research Updates paper – Understanding how Sclerotinia sclerotiorum initiates stem rot: factors affecting the germination of sclerotia
- For further information on the SclerotiniaCM app and how it was validated in the 2018 season, see 2019 Grains Research Updates paper – Tailored management of Sclerotinia in canola
- 2019 GRDC Research Update papers –
- 2019 GRDC Research Update presentations –
As the 2019 cropping season is getting underway additional further information on sclerotinia can be found in the following resources:
- Managing sclerotinia stem rot in canola – DPIRD
- Sclerotinia hub – The CCDM
- Sclerotinia stem rot in canola – GRDC factsheet
Kurt Lindbeck, NSW DPI