Kharbanda: Influences of Tillage on Blackleg and Other Diseases of Canola Grown in Rotation with Barley
Date: March 2001
Term: 4 years
Status: Completed
Researcher(s): Dr. Prem D. Kharbanda and Ralph Lange, Alberta Research Council, Vegreville, AB
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: Alberta Agricultural Research Institute, CCC, ACPC, MCGA
Project Summary
In the mid-1990s, given the introduction of several blackleg resistant canola cultivars and the widespread adoption of reduced tillage systems, growers were interested in finding out if canola could be planted more often within a rotation. However, limited information was available on how shorter rotation intervals would affect blackleg and other diseases of canola. Researchers conducted a four-year project at Viking, Alberta from 1996 to 2000 to determine the effects of tillage systems and crop rotations on the severity of canola diseases. Overall the study showed that all cultivars showed reductions in disease levels in response to longer rotation. Growers who adopt short rotations risk substantial yield losses, even if resistant cultivars are used. The project also demonstrated that reduced tillage does not increase the severity of blackleg and other diseases of canola.
With the introduction of several blackleg resistant canola cultivars and the widespread adoption of reduced tillage systems, growers were interested in finding out whether or not rotations could be shortened. However, limited information was available on how shorter rotation intervals would affect blackleg and other diseases of canola. Researchers initiated a four-year project at Viking, Alberta from 1996 to 2000 to determine the effects of tillage systems and crop rotations on the severity of canola diseases.
Included in the study were two Brassica napus cultivars, Quantum (resistant) and Westar (highly susceptible) and one B. rapa cultivar, Reward (susceptible). Westar and Quantum were rotated with Lacombe barley and Reward was rotated with Harrington barley. All crops were seeded in 1995 to Westar to prepare for the study. The crop rotation compared continuously grown canola with one, two or three canola crops grown in rotation with barley over four years. The tillage treatments consisted of conventional tillage (one pass with disk harrows, followed by two passes with a cultivator fitted with sweeps and spring harrows) and reduced tillage (no disturbance except for a fertilizer deep-banding pass prior to seeding).
The results of the study show that the crop rotations did have a strong impact on disease severity in general. The beneficial impact of rotation of canola with barley was reflected in the seed yield data. Both Quantum and Westar canola consistently yielded over 30 bushels per acre when grown once or twice over four years, but Westar yield decreased substantially when grown three or four years out of four. Measurable yield losses due to short rotation interval were seen in Quantum. The project also demonstrated that reduced
tillage does not increase the severity of blackleg and other diseases of canola. Overall, tillage treatment had no effect on blackleg severity, but it did tend to decrease the severity of root rot. Therefore, the research showed farmers can adopt reduced tillage systems without increasing the risk of losing yield to disease, provided recommended rotations are followed.
Soil moisture treatments applied in growth chamber studies indicated that soil moisture does not significantly affect blackleg severity. Overall, the comparison of disease severity and incidence data with climate data revealed no relationship between soil temperature, soil water potential nor precipitation.
The study concluded that all cultivars showed reductions in disease levels in response to longer rotation. This study was also the first one to show indications that economically significant yield losses due to disease can occur when genetically-resistant canola cultivars are grown in short rotations. Also, intensive cultivation of a cultivar resistant to the prevalent strains of blackleg could lead to the development of new strains of virulent blackleg. Growers who adopt short rotations risk substantial yield losses, even if resistant cultivars are used. The research also showed farmers can adopt reduced tillage systems without increasing the risk of losing yield to disease, provided recommended rotations are followed.