Yield loss of winter oilseed rape in relation to severity of stem canker (Leptosphaeria maculans ) in the UK

The relationships between yield loss and incidence or severity of stem canker in winter oilseed rape were analysed using data from experiments at Rothamsted in 1991/92, Withington in 1992/93, Boxworth in 1993/94 and Rothamsted in 1997/98. Critical point models and area under disease progress curve (AUDPC) models were better than multiple point models for describing relationships between yield (t ha-1) and incidence or severity of stem canker. Since yield in t ha-1 is influenced by many factors other than disease, % yield loss was calculated. Critical point models and AUDPC models relating % yield loss to stem canker were constructed and models for different experiments were compared. A critical point model relating % yield loss to stem canker incidence (GS 6.3-6.4), and AUDPC models for incidence or severity from growth stages 4.8 to 6.4 were derived from the combined data sets for the three experiments. The relationships between % yield loss and % plants with different stem canker severity scores at different growth stages, and between % yield loss and incidence or severity of both basal stem cankers and upper stem lesions were also analysed