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Latest on Canola disease – 2018 GRDC Update Papers

Canola close up

Keep up with the latest research information on canola diseases including blackleg and sclerotinia. The following papers and key messages were presented at the GRDC Updates across Australia in February and March 2018.

Read the key messages below and click the paper titles to view the full papers.

Southern Region

Blackleg in canola: an update on resistance, upper canopy infection and a new management app

Authors: Susie Sprague (CSIRO), Steve Marcroft (Marcroft Grains Pathology), Art Diggle (DPIRD), Angela van de Wouw (University of Melbourne), Kurt Lindbeck, Rohan Brill (NSW DPI), Andrew Ware (SARDI), Ravjit Khangura, Andrea Hills (DPIRD).

In 2017, blackleg leaf infection and resultant crown canker severity was low due to dry conditions in May and June during early seedling growth. Susceptible cultivars still had some level of disease but were well protected by fungicides applied at sowing, which were highly effective due to the lower disease pressure. Application of foliar fungicides at the 4 to 6 leaf stage was generally not warranted. In 2016 and 2017, upper canopy infection (UCI) caused large yield loss (up to 1t/ha) but the prevalent symptoms varied between years; pod lesions in 2016, stem and branch lesions in 2017. Delayed flowering after mid-August reduced severity of UCI in medium rainfall environments. Although flowering time is one important factor in the development of UCI, seasonal conditions relating to spore development and release, as well as infection events interact to produce UCI. Further research is required to understand and predict these interactions. Effective major gene resistance provides control of pod, branch and stem infection. Fungicides also control UCI however, further research is required to determine robust recommendations for foliar fungicide timing and determining the economic returns. The Blackleg Management App (‘BlacklegCM’ due for release February/March 2018) has been developed to provide growers and advisers with an interactive interface to explore the economic outcomes of different blackleg management strategies and their relative importance.

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Western Region

Factors affecting sclerotinia stem rot infections in canola

Authors: Sarita Bennett, Kyran Brooks, Michael Ashworth, Matthew Denton-Giles and Pippa Michael, Centre for Crop and Disease Management, Curtin University

When conditions are ideal for canola, over half of Sclerotinia sclerotiorum lesions can be removed from the stubble following Harvest Weed Seed Control (HWSC) guidelines. The numbers of sclerotes left in the soil following a badly infected sclerotinia stem rot crop is highly variable, but can be significant in patches. Rotation of canola with non-host crops is therefore recommended. Even in a dry and late start to the season sclerotinia stem rot infection was recorded in up to 10% of plants, however the severity of infection and subsequent yield loss was less. It is estimated that, if a better understanding of factors affecting sclerotinia stem rot infection of canola led to improved management of the disease and an increase in yield, by as little as 1%, then the benefits to WA grain growers will be close to $1.5 million per annum.

Understanding how Sclerotinia sclerotiorum initiates stem rot: factors affecting the germination of sclerotia

Authors: Ciara Beard and Anne Smith, DPRID, Geraldton

Under laboratory conditions germination of sclerotia of Sclerotinia sclerotiorum is favoured by a night/day temperature of 10/20°C. No germination at a higher night/day temperature of 16/29°C and exposure to this high temperature reduced the ability of sclerotia to subsequently germinate when they were moved to a 10/20°C night/day temperature. Understanding the temperatures that favour germination of sclerotia can assist with identifying the potential period in which ascospores may be produced in a given location. In an average year, and assuming sufficient moisture is available, this is likely to be May-October in cooler climates like Esperance, and June-September in warmer climates like Mingenew. Whether this period overlaps with the flowering window of canola crops will determine the risk of stem rot developing in a given season. Under a favourable night/day temperature of 10/20°C and ongoing moisture conditions, sclerotia germinated and many produced multiple apothecia (small mushroom like structures) at a time. Some sclerotia were able to produce additional apothecia subsequent to the ones produced when they first germinated and these survived from two to five weeks each over a three month period. This research shows that if favourable weather conditions persist, a steady production of ascospores can be released from one sclerote over several months. Some sclerotia were able to produce additional apothecia subsequent to the ones produced when they first germinated. Sclerotia that were ground to simulate the effects of seed destructor technology were still able to germinate under laboratory conditions. Apothecia produced from ground up sclerotia were smaller than those produced from intact sclerotia. Turning the sclerotia into a ‘flour’ (<0.5mm), however, significantly reduced and delayed germination.

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