Holzapfel et al: Effects of Genetic Sclerotinia Tolerance and Foliar Fungicide Applications on the Incidence and Severity of Sclerotinia Stem Rot Infection in Argentine canola
Date: March 2016
Term: 3 years
Status: Completed
Researcher(s): Chris Holzapfel, Indian Head Agricultural Research Foundation, Indian Head SK, S. Brandt, Northeast Agriculture Research Foundation, Melfort SK, D. McLaren and R. Mohr, AAFC Brandon Research Centre, Brandon MB, S. Chalmers and D. Tomasiewicz, Westman Agricultural Diversification Organization, Melita MB, R. Kutcher, University of Saskatchewan, Saskatoon SK
SaskCanola Investment: n/a
Total Project Cost: n/a
Funding Partners: n/a
Project Summary
Sclerotinia stem rot causes significant yield loss for canola in western Canada each year; however, the impact to individual fields varies dramatically depending on specific environmental and weather conditions. A three-year project was conducted to study the benefits and limitations of both genetic tolerance and foliar fungicide applications to manage this disease. Overall, the results showed that tolerant hybrids are effective for reducing disease and less likely to benefit from fungicide. There was also no benefit to dual applications over single applications, regardless of application timing or location. The greatest challenge for managing sclerotinia in canola continues to be accurately predicting whether yield responses to costly fungicide applications are likely.
Sclerotinia stem rot causes significant yield loss for canola in western Canada each year; however, the degree to which this disease affects individual fields varies dramatically depending on specific environmental and weather conditions. Although commercial tolerant hybrids are now available, sclerotinia infection is not eliminated in them and conditions may exist where foliar fungicide applications are still recommended. The combination of tolerant hybrids with fungicide applications may reduce the potential for the pathogen to overcome individual control measures, which is important since past experience has shown that relying heavily on any single technology is often risky and unsustainable. This project was initiated to enhance current understanding of the benefits and limitations that might be expected with both genetic tolerance and foliar fungicide applications.
A three-year field study was initiated in 2013 at five locations including Indian Head, Melfort and Outlook in Saskatchewan and Melita and Brandon in Manitoba. The objectives of this study were to evaluate the relative effectiveness of genetic tolerance and foliar fungicides to reduce sclerotinia stem rot infection in canola under field conditions. Researchers also wanted to determine if, and under what conditions, foliar fungicide applications may still be required when growing a hybrid with genetic tolerance to sclerotinia.
For the field study, two of the locations had access to irrigation and all of the locations were considered to at least have a moderate risk for sclerotinia in canola based on their climates. The plots at Outlook and Brandon received frequent, light irrigation through flowering to create conditions more favourable for disease development, while the other locations did not. The treatments compared two canola hybrids, 45H29 RR (susceptible) and 45S54 RR (tolerant), and four foliar fungicide treatments, including: untreated check, fungicide applied at 20% bloom, fungicide applied at 50% bloom and fungicide applied at both crop stages. The data collected from each plot included spring plant density (to assess overall stand density and variability), mean disease incidence (% MDI), mean disease severity (0-5 MDS), seed yield, seed weight and percent green seed.
The project results showed that while overall environmental conditions, subsequent disease pressure and canola yields varied across location-years, actual disease incidence was generally quite low, averaging less than 5% and only exceeding 10% in one in 14 cases. Therefore treatment effects were fairly subtle. Under the conditions encountered, disease levels were frequently lower for the tolerant hybrid 45S54 relative to 45H29, which is susceptible to sclerotinia. Fungicides reduced disease in the susceptible but not the tolerant hybrid where disease levels were low, regardless of fungicide treatment.
The results showed a slight but significant yield increase with fungicide when averaged across locations and hybrids. However, the economic returns associated with the applications would at best be marginal depending on grain and fungicide costs. Although not significant, there was limited evidence that the yield response was slightly larger and more consistent with the susceptible versus the tolerant hybrid. The results also showed no benefit to dual applications over single applications with regard to either visual symptoms or actual seed yields, regardless of application timing or location. As well, under this low disease pressure, there were no measurable benefits to applying fungicides with a tolerant hybrid.
Overall, the results showed that tolerant hybrids are effective for reducing disease and less likely to benefit from fungicide. However, susceptible hybrids may frequently yield higher, at least under low disease pressure as encountered in these trials. The greatest challenge for managing sclerotinia in canola continues to be accurately predicting whether yield responses to costly fungicide applications are likely. Genetic tolerance is an exciting advancement that has potential to reduce dependence on fungicides and provide adequate protection under low to moderate disease pressure. However, to be widely adopted and utilized to its full potential, sclerotinia tolerance should be incorporated into broader range of hybrids and, given the sporadic and unpredictable nature of this disease, yields must remain competitive with susceptible hybrids.