Control of Blackleg of Canola
Date: 1994
Term: 2 years
Status: Completed
Researcher: Dr. Prem D. Kharbanda, Alberta Environmental Centre
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: Canola Council of Canada, Alberta Canola Producers Commission, Alberta Agricultural Research Institute
Project Summary
The blackleg disease of canola, caused by Leptosphaeria maculans, has resulted in serious economic losses to canola crops on the Prairies. In the early 90’s, researchers initiated a project to develop an economical control of blackleg by integrating the use of disease tolerant cultivars, crop nutrition, seed treatments and timing of fungicidal sprays. Field and growth chamber experiments were conducted to evaluate large dosages of seed treatment fungicides and the influence of zinc in combination with an early application of prochloraz foliar spray. Overall, the fungicidal spray did not show any effectiveness to control blackleg in canola, most likely because of the tolerance of the cultivar. As well, the disease severity was not significantly reduced with the use of zinc soil treatments.
In the early 90’s blackleg disease of canola, caused by Leptosphaeria maculans, had resulted in serious economic losses to canola crops on the Prairies. Blackleg can be spread by wind-borne spores, which are not controlled by seed treatments. Researchers wanted to find out if extra-large dosages of a registered seed treatment fungicide might protect the seedlings of recently licensed moderately tolerant cultivars from infection at the critical early crop stage. A 1990 report from France had indicated that the micronutrient zinc suppressed toxin production by the blackleg fungus, so researchers also wanted to see if that might be an option in the Canadian prairies.
Researchers initiated a project in 1993 to develop an economical control of blackleg by integrating the use of disease tolerant cultivars, crop nutrition, seed treatments and timing of fungicidal sprays. A combination of field and growth chamber experiments was conducted on canola to evaluate large dosages of seed treatment fungicides, carbathiin (Vitavax RS or UBI 2617) and the influences of zinc in combination with an early application of prochloraz (Sportak) foliar spray to control blackleg. The cultivars tested included Brassica rapa cv. Tobin, B. napus cvs. Cyclone and Legend that were moderately tolerant to blackleg, and the highly susceptible B. napus cv Westar as a check.
Field experiments were conducted in farmer fields heavily infested with blackleg to evaluate large dosages of seed treatment fungicides to control blackleg and in combination with an early application of fungicidal foliar spray. Seed of the four cultivars was coated with carbathiin and thiram (Vitavax RS) at the commercially recommended rate of 22.4 mL/kg seed. For the higher rates, 2.5x and 5.0x the normal rate, UIB 2617 was used to keep the levels of insecticide lindane at the normal level. Disease severity and grain yield were analyzed. Foliar spray of Sportak was applied at 500 g a.i./ha at four different timings. Growth chamber experiments were also conducted using some of the treated seed of the four cultivars prepared for the field experiment.
The results of the field experiments showed that the check Westar responded well to the high dosages of seed treatments, the 5x normal dosage results in significantly more healthy seedlings than in the normal dosage. However, there was no decrease in the final disease severity levels or increase in yield at the higher dosages of seed treatments as compared to the recommended rates. In the plots that were treated with both seed treatments and fungicidal foliar spray, there was no significant control of blackleg by spraying prochloraz and overall there was no increase in yield in either of the two cultivars tested, Legend and Tobin. The lack of effectiveness of fungicidal control may be because the cultivar Legend possesses some tolerance to the disease. Results from the growth chamber trials were similar, with some initial improvement but overall no final increase in yield or reduction in disease severity levels.
Field and growth chamber studies were also conducted to determine the influence of zinc and an early application of fungicidal foliar spray to control blackleg on the cultivar Legend and the check Westar. In the field experiment, plots were either untreated, or treated with chelated zinc at 25kg/ha as required after a soil test. The same seed and foliar fungicide treatments were used as in the first trial. Overall, there was no control achieved with the application of zinc in the trials. The disease severity was not significantly reduced with the use of zinc soil treatments.
Table 14: Effect of soil amendment with zinc and of a foliar spny with prochlonz on blaclcleg severity and grain yield of canola cv. Legend in an infested field, 1993.
Mean of 4 replications; mean in columns followtd by the same leuerdo not differ significantly according to Duncan's Multiple Range Test (P=0.05). Disease severity rated on a scale of
0 (Healthy) - S (Dead).