Effect of blackleg and sclerotinia stem rot on canola yield in the high rainfall zone of southern New South Wales, Australia
John A Kirkegaard A E , Michael J. Robertson B , Peter Hamblin C and Susan J. Sprague A DA CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia.
B CSIRO Sustainable Ecosystems/APSRU, Queensland Biosciences Precinct, 306 Carmody Rd, St Lucia, Qld 4067, Australia.
C Agritech Crop Research, PO Box 678, Young, NSW 2594, Australia.
D School of Botany, The University of Melbourne, Vic. 3010, Australia.
E Corresponding author. Email: John.Kirkegaard@csiro.au
Australian Journal of Agricultural Research 57(2) 201-212 https://doi.org/10.1071/AR05179
Submitted: 24 May 2005 Accepted: 28 October 2005 Published: 24 February 2006
Abstract
Canola (Brassica napus) yields have been declining in the medium–high rainfall (550–650 mm) areas of southern NSW during the 1990s. This decline is not related to seasonal conditions and is not evident in wheat. Leading growers and consultants suspect that increasing levels of the diseases blackleg, caused by Leptosphaeria maculans, and sclerotinia stem rot, caused by Sclerotinia sclerotiorum, may be responsible. We investigated the effect of these diseases on otherwise well-managed canola crops at 2 sites in southern NSW from 2001 to 2003. Blackleg was present at both sites in all 3 years, with 8–10% of plants of variety Rainbow lodged in the untreated plots at Galong in all years, and 1–10% at Wallendbeen. Sclerotinia stem rot was predominately confined to 2001 when 7–42% of plants were infected in the untreated plots at the sites. Individually, or in combination, the diseases caused significant yield losses at both sites in every year of the study, ranging from 0.39 t/ha to 1.54 t/ha. These findings suggest that for each 1% reduction in the incidence of blackleg lodging, yield was increased by 5%, whereas each 1% reduction in plants infected with sclerotinia stem rot increased yield by 1.3%. The ability of the crops to yield to their simulated water and N-limited potential when these diseases were either absent or controlled, indicates that disease may be the key yield-limiting factor in the area. Cost-effective control strategies for both diseases are critical if canola is to remain an important and profitable break crop in the farming system in the high-rainfall zone of southern NSW.
Additional keywords: Leptosphaeria maculans, Sclerotinia sclerotiorum, Brassica napus, Phoma stem canker.
Acknowledgments
We thank Grain Growers Australia and Grains Research and Development Corporation for funding this work through the Best Bet Canola Project administered by Harden and District Rural Advisory Service with advice from Best Bet Canola Management Committee. We also thank Mr Charlie Baldry, Mr Steve Woodhead, and Mr Neil McColl for use of their land for the experiments, and Mr Geoff Howe, Mr John Graham, and Mr Peter Hines for expert technical assistance.
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