Occurrence and impact of blackleg on oilseed rape in Ontario

aetiology brassica napus crop yield disease prevalence disease surveys encuestas sanitarias epidemiologia epidemiologie epidemiology etiologia etiologie hiver invierno leptosphaeria maculans losses oilseeds ontario pathogenicity perte primavera printemps rendement rendement des cultures rendimiento rendimiento de cultivos semillas oleaginosas spring strains virulence winter yields