THE EFFECT OF CROP-ROTATION ON DEVELOPMENT OF THE SEPTORIA DISEASE COMPLEX ON SPRING WHEAT IN SASKATCHEWAN

Disease epidemics caused by the complex of septoria diseases on spring wheat cultivars were studied in the Parkland region of Saskatchewan. Both Phaeosphaeria (Leptosphaeria) nodorum and Mycosphaerella graminicola were prevalent when average rainfall was received, but under dry conditions P. nodorum was the predominant pathogen. Neither P. avenaria nor Pyrenophora tritici-repentis were considered to be of importance. Area under the disease progress curve (AUDPC) and curve-fitting methods were useful in describing the epidemics. Resistance to the septoria disease complex, expressed as lower AUDPC or longer time to 50% disease severity, was greatest for cv. Oslo, intermediate for Katepwa and Pembina, and least for Kenyon. Crop rotation was effective in reducing the severity of the epidemics. When conditions were unfavourable for disease development, a rotation of one year between wheat crops was as effective as two years in reducing disease severity. However, under more favourable conditions, a rotation of two years between wheat crops resulted in the greatest reduction and provided adequate control of the septoria disease complex.