Seed & Chemical
Blackleg and risk management
By Donna Fleury
R-rated blackleg resistance used to be the cornerstone for managing blackleg in canola, but is it enough now? Blackleg continues to be detected in disease surveys across the Prairies, with 2012 showing the highest levels in recent years and 2013 also causing concern. Industry and growers are being encouraged to build risk management approaches into their systems when dealing with blackleg to keep the Canadian canola industry profitable and resilient.
“Recently, some agronomists are finding fields where farmers were growing R-rated blackleg varieties that had higher than expected levels of blackleg disease,” says Clint Jurke, agronomy specialist with the Canola Council of Canada (CCC). “With tighter crop rotations, this is a risk that needs to be addressed by growers and industry. It is also the motivation for CCC initiating discussions with industry to try to come up with a better way of informing growers to make more strategic blackleg management decisions.”
Current research, led by Dr. Dilantha Fernando at the University of Manitoba and Dr. Gary Peng with Agriculture and Agri-Food Canada (AAFC) in Saskatoon, is trying to characterize resistance genes in many of the commercial canola varieties. “This research work is crucial for our basic understanding of how much genetic variability we have in the resistance genes currently being used,” explains Jurke. “So far, the initial research data shows that the majority of varieties are relying on one resistance gene, Rlm3. As a result, the pathogen has responded accordingly and races are being selected that are virulent against that type of resistance.”
This may be a risk to the canola industry, and one that is going to require an industry strategy. “We may need to develop a better strategy of how we communicate blackleg risk and perhaps how we identify resistance in our varieties so growers can make better informed choices,” says Jurke. “Once canola growers start selecting for some of these more aggressive, more virulent races on a regular basis, and as these races become more dominant, then our current resistance strategy as a whole becomes compromised. We are in the early stages of seeing blackleg troubles, but we have the opportunity right now by tweaking our existing systems to stay ahead of blackleg in Canada. We don’t want to create a situation where blackleg is a huge problem for the entire industry such as it was in the 1980s and ’90s in Canada.”
Industry is beginning to see the need in the marketplace for more diversity in resistance in canola varieties. Some companies are developing varieties with more than one type of resistance in the germplasm. “We are looking forward to discussions with industry to address these needs, and to come out with a model on how to manage the risks,” notes Jurke. “In the meantime, we are working with growers to take a risk management approach to dealing with blackleg in their rotations.”
Blackleg risk assessment and management
The CCC has developed a risk matrix that helps growers assess strategies and implement low-risk decisions for blackleg management (see chart above). Growers are encouraged to conduct a risk management assessment and to implement good management practices when developing a risk management strategy. Risks are listed in terms of importance, with rotation being most important. If growers follow a tight rotation, then using other low-risk measures helps reduce the overall risk.
Jurke explains that the risk management approach has three main levels of control: scouting, crop rotations and variety rotations. Scouting is the first step and growers need to identify whether or not they have any fields where blackleg levels are high. Learning to identify blackleg properly and scout for the disease at the end of the season is important.
Crop rotation is the second important control strategy, and long-term crop rotations are ideal and especially recommended where blackleg levels are high. Any field where more than 50 per cent of the stems are infected with blackleg is a field of concern. “If growers have a field where blackleg levels are high, then they should move that field into a long-term crop rotation (four years) strategy,” says Jurke. “This is especially important for growers using tight rotations. Although growers might not have experienced a yield loss if the severity is low, certainly the next time they grow that same variety in that field, it could be epidemic proportions.”
It takes two to three years for blackleg-infected canola stubble to decompose to the point where infection risk to the next crop is significantly reduced. The best strategy is to move these fields with high levels of blackleg infection into a long-term crop rotation, but if that is difficult financially then growers should move to the third level of control or variety rotation.
Variety rotation is important, and although there isn’t a listing available in Canada, the recommendation is for growers to not use the same variety on the same field in a tight rotation. “If growers really like variety ‘X’ but had some blackleg in it and the field has more than 50 per cent of the stems infected, then choose variety ‘Y’ from the same company or try a new variety from a different company,” recommends Jurke. “In a tight rotation it is also a good idea to rotate between Roundup Ready and Liberty Link systems, which is recommended for volunteer control and weed resistance management issues.”
Growers and industry need to continue to work together to develop a proactive risk management approach to blackleg. Australia already categorizes canola varieties based on specific blackleg resistance genes. The CCC is working together with industry and growers to develop blackleg management strategies, which may include a new variety rotation scheme that is appropriate for Canada.