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Blackleg Disease Management – Cultural Controls Ralph Lange Alberta Innovates – Technology Futures Is there a place for cultural control methods? Disease contingent on Host/Pathogen/Environment triangle Long-lasting control requires integrated approach Cultural control can disrupt disease cycle Integrated approach can slow breakdown of genetic resistance Forms of cultural control applicable to blackleg: Crop rotation Sanitation Tillage Burning Disease-free seed/seed treatment Crop rotation decreases blackleg severity Severity (0-5) 3.5 3 % incidence 2.5 2 Clear reduction in severity due to oneor two-year break with wheat or wheatfallow (Carman, MB Guo et al.2005) 1.5 1 0.5 0 CCCC CWCC CCWC CWFC Crop rotation decreases blackleg severity 3.5 Severity (0 (0-5) 3 2.5 2 1.5 1 0.5 0 1 2 3 Crops/4 years Westar Quantum Lange & Kharbanda, 2002, Viking, AB 4 Crop rotation decreases blackleg incidence 100 % Incidence 80 60 40 20 0 1 2 3 Crops/4 years Westar Quantum Lange & Kharbanda, 2002, Viking, AB 4 Canola Cropping Frequency Black DG East soil zone Based on AFSC data 500 canola on canola 1 year break 2 year 3 year 4+ on fallow 450 400 350 Records 300 250 200 150 100 50 0 2004 2005 2006 2007 2008 2009 Tillage in western Canada Conventional AB Conservation No-till SK MB 0 10 20 Seeded ha (‘000,000) Statistics Canada, 2007, Selected Historical Data from the Census of Agriculture: Table 5.1, Does tillage reduce blackleg? 90 Significant effect of tillage on blackleg incidence and severity (Carman, Conventional 80 % incidence 70 60 50 40 Zero 30 20 10 0 CCCC CWCC CCWC CWFC MB Guo et al.2005) Does tillage reduce blackleg? 8 Significant effect of tillage on blackleg incidence and severity (Carman, Conventional 7 Severity (0 (0-9) 6 5 4 Zero 3 MB Guo et al.2005) No sig. effect (Melfort, SK Bailey et al.2000) 2 1 Low disease pressure 0 1994 1995 1996 1997 Does tillage reduce blackleg? 5 Severity (0 (0-5) 4 3 2 1 0 Significant Conventional effect of tillage Zero on blackleg incidence and severity No sig. effect No tillage effect, even under higher disease pressure (Lange & Kharbanda, 2002, Viking, AB) Effect of tillage on primary inoculum Tillage buries shoot tissue, conservation tillage leaves more tissue on surface Non-linear relationship with surface residue and blackleg disease (Turkington et al. 2000) Burial encourages formation of pseudothecia over pycnidia(Kharbanda & Ostashewski 1997) Seeding operations bring residues to surface Burning crop residues Fields burn unevenly Low-moisture tissue burns, high moisture tissue remains Low moisture=upper stems, branches, etc High moisture = stem bases, where pseudothecia are concentrated Raking + burning reduced ascospore release (Australia, Khangura et al, 2007) Atmospheric carbon, soil OM, air pollution, etc. Burning Many unburned areas Burnt areas What’s the real objective? Ascospore load important determinant of disease severity (Wherrett et al 2004): >25×105 ascospores/stem maximizes disease in adult plants 5×105 to 25×105 ascospores/stem reduces disease incidence Management objective: limit viable primary inoculum on soil surface in susceptible period Can this be done without tillage in short rotations? Possible strategies to reduce Primary inoculum without tillage Mechanical disruption of lower stems Mower, flail mower? Stubble-applied fungicides? Sulphur,copper? Stubble-applied fertilizers Enhance microbial decomposition? Possible strategies to reduce Primary inoculum without tillage Biological control by antibiosis Paenibacillus polymyxa Streptomyces halstedii, S. rochei Possible strategies to reduce Primary inoculum without tillage “Stubble degraders” Cyathus olla Ceriporiopsis subvermispora/Cellul omonas sp./Azospirillum brasilense consortium (sugarcane bagasse) Summary Reduction of canola rotational interval to less than 1 crop/2 years unlikely in many areas Switch from conservation tillage/zero tillage unlikely or ineffective except in some areas Need technologies that reduce inoculum load in fields without relying on rotation or tillage