Time of sowing and fungicides affect blackleg (Leptosphaeria maculans) severity and yield in canola
R. K. Khangura A C and M. J. Barbetti BA Department of Agriculture, Western Australia, Locked Bag No. 4, Bentley Delivery Centre, WA 6983, Australia.
B School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, Crawley, WA 6009, Australia.
C Corresponding author. Email: rkhangura@agric.wa.gov.au
Australian Journal of Experimental Agriculture 44(12) 1205-1213 https://doi.org/10.1071/EA03178
Submitted: 4 September 2003 Accepted: 30 April 2004 Published: 24 January 2005
Abstract
Three different times of sowing in conjunction with various fungicide treatments were evaluated for the management of blackleg in canola (Brassica napus L.) variety Karoo. The trials were conducted at 4 different locations in Western Australia: East Chapman, Merredin, Wongan Hills and Mt Barker, representing a range of environmental conditions. The first time of sowing was at the break of the season followed by 2 subsequent sowings about 3 and 6 weeks later. Blackleg severity was significantly reduced by 14% when sowing was delayed until the end of June or early July, however, there were yield penalties due to the shortened growing season. Yield losses from blackleg were 16, 38 and 34% for mid-May, early to mid-June and end June to early July sown crops, respectively. All the fungicide treatments substantially reduced blackleg severity and increased yields at all the locations except for East Chapman (low rainfall site). The maximum protection fungicide treatment (Jockey seed dressing at 6.6 g a.i./kg seed + Impact in-furrow at 100 g a.i./ha + 3 foliar applications of flusilazole at 100 g a.i/ha) improved seed yield by 47, 56, 46 and 16% at Merredin, Wongan Hills and Mt Barker and East Chapman, respectively, compared with the nil treatment. Averaged over time of sowing and locations, the treatments of Jockey and Impact reduced disease severities by 20 and 25% and increased seed yields by 19 and 24%, respectively. There is potential for some other fungicide treatments, such as seed dressing with Jockey in combination with foliar application of either flusilazole or prochloraz, for the control of blackleg.
These investigations suggest that damage from blackleg, in some areas during some seasons, could be minimised by sowing canola crops as early as possible before the onset of maturation of pseudothecia thus avoiding major ascospore showers at the seedling stage of maximum susceptibility. However, in case of a late break of season, fungicide protection may be essential to minimise losses from blackleg, particularly if sowing moderately susceptible cultivars under moderate to high disease pressure situations.
Additional keywords: disease management, Brassica napus, crown cankers, cultural practices.
Acknowledgments
We thank Dr Elaine Davison, Department of Agriculture, WA, for critically reviewing the manuscript; Ms Jane Speijers, Department of Agriculture, WA, for help with the statistical analysis and Mr M. Aberra for providing technical assistance. We gratefully acknowledge the Grains Research and Development Corporation for funding this research.
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