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RESEARCH ARTICLE (Open Access)

Influence of crop and stubble management practices on blackleg disease of canola (Brassica napus) in Australia

Susan J. Sprague https://orcid.org/0000-0002-2622-645X A * , Steve J. Marcroft B , Kurt Lindbeck C , Elizabeth M. Sheedy B and Angela P. Van de Wouw https://orcid.org/0000-0001-5147-0393 D
+ Author Affiliations
- Author Affiliations

A CSIRO, Canberra, ACT 2601, Australia.

B Marcroft Grains Pathology, Horsham, Vic 3400, Australia.

C Department of Primary Industries and Regional Development New South Wales, Wagga Wagga, NSW 2650, Australia.

D School of BioSciences, the University of Melbourne, Parkville, Vic 3010, Australia.

* Correspondence to: susan.sprague@csiro.au

Handling Editor: Christian Huyghe

Crop & Pasture Science 76, CP24385 https://doi.org/10.1071/CP24385
Submitted: 4 January 2025  Accepted: 2 April 2025  Published: 30 April 2025

© 2025 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

Context

Australian canola (Brassica napus) growers have shifted towards earlier sowing and flowering times in addition to the widespread adoption of stubble conservation practices.

Aims

This study determined the consequent impact of these crop and stubble management practices on blackleg crown canker and upper canopy infection caused by the stubble-borne pathogen Leptosphaeria maculans.

Methods

Ascospore maturation and release were measured across seasons in commercial canola crops in south-eastern Australia on standing/erect and lying/knocked down stubble. We determined the severity of blackleg crown canker and upper canopy infection in crops with early or late sowing and flowering windows exposed to different stubble treatments.

Key results

Ascospore maturation was delayed and ascospore release was 10-fold lower in standing stubble in the first season post-harvest. In the second season when standing stubble was knocked down, total ascospore production was up to 4-fold higher than in the first season. Stubble orientation had no effect on blackleg disease severity. The main driver of infection at vulnerable crop stages was determined by sowing and flowering times such that disease severity was reduced by 35–76% and 98% in early sown and later flowering crops, respectively.

Conclusions

Canola grown in short rotations or intensively within a landscape will be exposed to high blackleg inoculum loads from retained stubble. Revision of current blackleg recommendations are required to account for modern crop management practices.

Implications

Innovative blackleg control strategies are urgently required to safeguard host genetic resistance and fungicide efficacy in modern farming systems to ensure sustainable intensification of canola production in Australia and globally.

Keywords: ascospore release, crop residue, cultural practices, disease management, epidemiology, pathogen evolution, Phoma lingam, Plenodomus lingam.

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