POSTHARVEST SURVEYS OF BLACKLEG ON STUBBLE OF RAPESEED CANOLA CROPS IN SASKATCHEWAN, 1981-1991

In an area northeast of Prince Albert, Saskatchewan, the average incid ence of the virulent strain of Leptosphaeria maculans (blackleg) on st ubble in post-harvest surveys of rapeseed/canola crops increased from 14.5% in 1989 to 52.6% in 1991. Over the same three year period its av erage incidence west of Saskatoon increased from 59.4% to 92.6%. In bo th areas there was also a substantial increase in the frequency of fie lds with over 50%. blackleg incidence. In the relatively remote areas west of Prince Albert and near Meadow Lake, the average incidence of v irulent blackleg in 1990 was 25 and 21%, respectively. Since virulent blackleg was initially found in Saskatchewan in 1975, its prevalence a nd incidence have increased at a slower rate in northern growing areas than in those farther south.