Grains Research and Development

Date: 30.06.2015

Blackleg

Blackleg

Generally, blackleg is more severe in areas that receive high rainfall and have intensive canola production. However, it can be present if unseasonably high rainfall occurs in lower rainfall regions in paddocks sown in close proximity to the previous year’s canola stubble. Fungal spores are released from canola stubble and spread extensively via wind and rain splash.

Blackleg is caused by the fungus Leptosphaeria maculans and is the most serious disease of canola in the medium to high rainfall production areas of Australia. Blackleg is normally successfully controlled, but yield losses of 50 per cent and greater have been recorded in worst affected cases. Where cultivar blackleg resistance has been overcome up to 90 per cent yield loss has been documented.

There is a very strong relationship between the intensity of canola production within a region and the level of blackleg development within commercial crops.  The blackleg pathogen survives and reproduces on the previous season’s canola stubble. Therefore a 500,000ha canola crop will result in 500,000ha of blackleg-infested stubble the following season, releasing windblown spores every time it rains.

Blackleg survives on canola stubble and produces fruiting bodies that contain large quantities of airborne spores (capable of travelling several kilometres). Autumn and winter rainfall triggers spore release from the fungal fruiting bodies. Within two weeks of spores landing on canola cotyledons and young leaves, visible off-white coloured lesions develop. These lesions produce pycnidial fruiting bodies (dark coloured dots), which release rain-splashed spores.

Once the lesion has formed, the fungus grows within the plant’s vascular system to the crown. The fungus causes the plant’s crown to rot, resulting in a canker. Less severe infection can still result in the restriction of water and nutrient flow within the plant. Blackleg symptoms can also been found in plant roots. In severe cases the fungus will cause the entire plant to die prematurely.

Management practices to control crown rot blackleg are the same for the root rot form of the disease.

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Steve Marcroft Media Releases

Canola growers urged to check revised blackleg ratings

Date: 11.04.2017

Grain growers in the southern cropping region are being urged to check the latest blackleg disease ratings for canola cultivars ahead of sowing in 2017. more

Blackleg management guide 2017 cover image

Blackleg Management Guide, 2017 Autumn Variety Ratings

GRDC Project Code: MGP0004

Date: 30.03.2017

Blackleg can cause severe yield loss, but can be successfully managed. Use this guide to determine whether you are in a high-risk situation and what practices you can change to reduce or prevent yield loss from blackleg. Follow the four steps, in sequence, below. more

Grains Research Updates

Managing canola diseases blackleg and sclerotinia

GRDC Project Code: DAN00177, UM0051

Author(s): Kurt Lindbeck and Audrey Leo (NSW - Department of Primary Industries, Wagga Wagga), Stephen Marcroft (Marcroft Grains Pathology) and Joop van Leur (NSW - Department of Primary Industries, Calala)

Date: 07.03.2017

• Impacts on yield due to blackleg of canola are likely to be lower in northern NSW compared to southern NSW.
• Growers should still be vigilant in managing this disease and an integrated approach should be adopted by growers that utilises variety resistance, cultural control and the strategic use of fungicides.
• Sclerotinia stem rot is a production issue where spring rainfall is adequate to provide long periods of leaf wetness in the presence of flowering canola crops.
• If there is a history of sclerotinia stem rot in your district causing yield loss, be prepared to use a foliar fungicide to reduce yield loss.
• Sclerotinia stem rot occurred in those districts with a frequent history of the disease in 2016. Wet conditions in spring were ideal for disease development.
• Extended periods of leaf wetness (at least 48 hours) are ideal for triggering epidemics of stem rot.
more

Grains Ground Cover

Flowering window dictates canola disease risk

GRDC Project Code: UM00051

Issue #127

Date: 06.03.2017

Costly canola yield losses from blackleg and sclerotinia stem rot can be alleviated by strategically timing flowering to occur outside the main winter period.
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