Peng: Mitigating the Risk of Blackleg Disease of Canola Using Fungicide Strategies
Date: March 31, 2015
Term: 4 years
Status: Completed
Researcher(s): Gary Peng, AAFC Saskatoon Research Centre, Saskatoon, SK, Dilantha Fernando, Dept. Plant Sciences, University of Manitoba, Winnipeg MB, and Ralph Lange, Alberta Innovates –Technology Futures, Vegreville, AB
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: MCGA
Project Summary
Blackleg, caused by Leptosphaeria maculans, used to be the most widespread fungal disease of canola in western Canada. The disease was well controlled for many years with resistant canola cultivars and extended crop rotation, but has increased noticeably in recent years. Researchers from western Canada conducted a four-year, multi-site study to assess the efficacy and yield benefit of fungicide strategies in blackleg management in case the varietal resistance erodes rapidly. The results show that fungicides generally do not pay if the cultivar resistance still holds or the disease pressure is light. In fields with increased blackleg incidence, crop and cultivar rotation should be considered first. If these measures don't alleviate the disease sufficiently, then a fungicide treatment may be considered when disease risk is high.
Blackleg, caused by Leptosphaeria maculans, is the most widespread fungal disease of canola in western Canada. It has the potential to greatly reduce canola yields and decrease economic returns of growers. Prior to 2010, growers primarily managed the disease with the use of resistant cultivars and 4-year crop rotations. However, in response to market signals many growers are producing canola in 2-year rotations across the Prairies. Consequently the risk of blackleg is increasing, which can be caused by changes in the pathogen population and the emergence of virulent pathogen strains against the current cultivars. This project takes a proactive approach by examining the efficacy and yield benefit of fungicide strategies in blackleg management in case the varietal resistance erodes rapidly.
Researchers from western Canada initiated a four-year, multi-site study in 2011 to assess the efficacy of foliar fungicides in mitigating the risk of severe canola yield losses caused by blackleg when cultivar resistance is overcome by the pathogen population. In the study, researchers also assessed treatment timing and multiple applications to determine the optimal efficacy of fungicide against blackleg. Field plots were established at Vegreville, AB, Scott and Melfort, SK and Brandon and Carman, MB between 2011 and 2014. The susceptible cv Westar was used to represent the worst-case scenario of resistance breakdown. Diseased canola residues from previous years were left in the plot area for pathogen inoculum.
Study treatments included applications of the strobilurin fungicides Headline, Tilt, Quadris® and Quilt Xcel® at the 2-4 leaf stage individually, in a split application (Headline then Tilt or vice versa) at the 2-4 leaf and prior to bolting, and Headline alone just prior to bolting. Unsprayed plots were used as a non-treated control. The resistant (R) cultivar 45H29 and moderately resistant (MR) cultivar 43E01 also were treated with Headline at the 2-4 leaf stage as additional checks. At crop maturity, blackleg incidence and severity were assessed on 50 plants by examining cross-sections of lower stems and tap roots in each plot. Seed yield was recorded after harvest.
Blackleg originating commonly from lower leaf infection, which underscores the importance of early fungicide treatment.
Overall, the study showed that the early application (2-4 leaf stage) of Headline, Quadris or Quilt Xcel reduced blackleg and increased canola grain yield significantly on Westar. However, Tilt or late application of Headline (prior to bolting) did not reduce the disease or increase the grain yield, relative to the non-treated control. As well, using two fungicide treatments with different action modes did not achieve better efficacy relative to a single application of Headline or Quadris at the 2-4 leaf stage. The average yield benefit was 3-4 bushels/acre for the early fungicide treatment, but it was likely more due to the benefit under severe disease cases with some of the trials.
In further analysis of data, researchers compared low (<1.0) and moderately high (>1.0) disease site-years and found several new trends emerging. These results showed that under low disease severity, none of the fungicide treatments reduced the blackleg or increased the yield substantially on Westar. For MR and R cultivars, the observations were similar, except that the disease incidence on the MR was reduced slightly, while the impact on yield was not significant. High disease conditions may be related to the erosion of cultivar resistance, high blackleg incidence/severity in the previous crop and short crop rotations.
Scouting after swathing/harvest is important to understanding the risk potential and making fungicide decisions. If blackleg is found on a high number of plants (say >30%) and the average severity is greater than 1 (Figure 1), then steps need to be taken to mitigate the risk by changing canola cultivar, extending crop rotation and considering a fungicide treatment if rotation is shorter than 3 years.
Figure 1. Blackleg severity scale (0-5) for disease assessment during harvest.
Despite the relatively high levels of disease observed at harvest on R and MR cultivars in some of the trials, the impact on canola yield appears to be limited and the fungicide treatment would provide little economic benefit. This may be related to a slower rate of disease development in R or MR cultivars. In fields with increased blackleg incidence, crop and cultivar rotation should be considered first. If these measures don't alleviate the disease sufficiently, then a fungicide treatment may be considered when disease risk is high.
Therefore, researchers recommend that fungicides should be considered for blackleg management only when disease pressure is high and the cultivar resistance is compromised. Strobilurin fungicides are effective against blackleg, and the early application (2-4 leaf stage) is more effective than a late treatment (rosette, prior to bolting). Multiple applications generally are not required for maximum efficacy.
Scientific Publications.
Peng G, Fernando WGD, Kirkham CL, Lange R, Kutcher HR, McLaren D, Johnson E, Turkington KT. 2012. Mitigating the risk of blackleg disease of canola using fungicide strategies. In Proc. Soil and Crops 2012. University of Saskatchewan Press (CD), Pp7.
Peng G, Fernando WGD, Lange R, Kutcher HR 2014. Blackleg of canola -new management strategies against an old disease in western Canada (Abstr.). Can. J. Plant Pathol 36:289.
Fernando WGD, Zhang XH, Liban, SH, Cross DJ, Peng G, Kutcher HR. 2014. A novel strategy for managing blackleg of canola on the Canadian prairies. Can. J. Plant Pathol 36:260.
Full Report PDF: Mitigating the Risk of Blackleg Disease of Canola Using Fungicide Strategies