Blackleg on the rise Superior genetics and pesticides make short rotations possible in canola crops, but can they be pushed too far?
As a consistent high profit generator, canola-seeded area has doubled in the past 10 years, mostly by reducing rotations from once every three or four years to once every other year or continuous.
However, short rotations encourage development of fungi and weeds able to overcome disease resistance in crops and herbicides. With the right weather circumstances last summer, many farmers saw crop disease severely limit yield.
Western Producer reporters Robert Arnason, Barb Glen and Robin Booker have compiled this special report looking at how canola’s success encourages pests that threaten its future.
All gamblers, at least sober gamblers, know the house eventually wins in Las Vegas.
For Randy Kutcher, a University of Saskatchewan plant pathologist, the Las Vegas analogy can be applied to tight canola rotations in Western Canada.
Producers may be rolling in money now, but over time the odds are stacked in favour of natural biological forces. It might take decades, but nature will find a way to defeat questionable agronomic practices such as tight rotations, he said.
Gary Peng, an Agriculture Canada blackleg and clubroot expert in Saskatoon, supported Kutcher’s analogy. He said the odds of a farmer winning or losing, in any given growing season, depend on rain, temperature and soil moisture.
“You may be able to get away with several cycles of a short rotation if the weather conditions work against the infection,” Peng said.
“We have been quite lucky for many years…. We have managed blackleg reasonably well until probably 2010, 2011 and 2012.”
The Manitoba canola disease survey from 2011 and 2012 indicated that 15 and 17 percent of fields respectively had significant levels of blackleg, even though the vast majority of canola varieties grown in the province are R-rated cultivars.
In Manitoba, volunteers and government staff inspect canola plants visually. Since blackleg can be difficult to detect it’s likely that provincial figures are higher, said Holly Derksen, Manitoba Agriculture plant pathologist.
“It’s being under-diagnosed. Even by our survey,” she said.
“I personally can’t walk into a canola field (in Manitoba) and not find blackleg…. I’m not saying every field I go into blackleg is causing yield loss. (But) it’s present.”
The data and anecdotal evidence from Manitoba suggests that blackleg-resistant varieties may be struggling to cope with a growing amount of inoculum in the soil.
“The risk is that the resistance breaks down in varieties and we may be seeing that in Manitoba,” Kutcher said.
“Varieties that are R rated aren’t doing so well in some growers’ fields.”
Agriculture Canada data from the Scott research farm in Saskatchewan clearly shows that yields decline in short rotations with a cultivar susceptible to blackleg. However, resistant cultivars in tighter rotations were able to maintain yields in the plot scale study, held over multiple years in the 2000s.
“We didn’t see a big yield loss in the two year, canola-wheat, versus the four year rotation,” said Stewart Brandt, a retired Agriculture Canada scientist who participated in the canola rotation studies in Saskatoon and Melfort, Sask.
The continuous canola results were more definitive.
“Even with the best varieties, best disease resistance and the best weed control available, we did see a yield loss in the order of 20 percent … on average, over the eight year period,” Brandt said.
The two year rotation also faltered near the conclusion of the study.
“When we got towards the end of the eight years, we started to see some yield reductions even with the two year rotations.”
Data posted on Alberta Agriculture’s website backs Brandt’s yield loss figures for continuous canola. Yields from canola grown on canola stubble drop by 16 percent compared to canola grown after a one or two year break.
Plot trial results may show that tight rotations put pressure on canola plants, but it’s difficult to know for certain that a concentration of canola acres will lead to a blackleg outbreak.
“These are things we can’t research in small plot trials,” Brandt said.
“It’s going to be very difficult to generate data that would substantiate or refute those things.”
Growers would ideally seed canola every third year, but Canada’s canola industry must adjust to the economic realities on the farm, said Al Eadie, manager of market development with Bayer Crop Science in Canada.
A rotation of canola-cereal-canola-cereal probably wouldn’t have worked a couple of decades ago, but it can today thanks to superior biotechnology, he added.
“Our studies in corn demonstrate that modern hybrids are better able to handle stress than hybrids a number of years ago,” he said.
“You can improve crop genetics to help handle the stresses associated with shorter rotations…. Better tools will be delivered. Better genetics, better seed treatment, better disease resistance with the crop cultivars and better utilization of sclerotinia fungicides.”
Eadie said the situation in Western Canada is comparable to the U.S. Midwest. Increased demand for corn and soybeans, combined with less livestock in the Midwest, has promoted a corn-beans-corn rotation.
Nonetheless, those crops shouldn’t be compared to wheat and canola, Brandt said.
“These crops (corn and soybeans) are huge crops globally and there is a great deal of investment into technologies that allow us to intensify their production,” he said.
“Whether or not we could duplicate that, even with that kind of investment in canola and wheat, is a question we can debate.”
He said canola growers shouldn’t expect plant scientists to provide all the solutions. Farmers must adopt best practices to mitigate the risks connected to tighter rotations, such as using herbicides appropriately to control volunteer canola.
“Make sure you’re doing a good job of controlling volunteer canola in your non-canola year,” Eadie said.
“(And) combine another herbicide with your glyphosate in your pre-seed application … in your canola year.”
Another tactic is to switch up the canola system, said Barry Chappell, a producer from Hamiota, Man.
Chappell has maintained a two-year canola rotation since 1997 and regularly rotates his canola system from Roundup technology to Clearfield. Rotating systems improves weed control, helps manage disease resistance and controls volunteer canola, he said.
“By not controlling volunteers, you start running into other issues of disease resistance of blackleg … and potential yield losses because … you’re not going to get the same production from volunteer plants.”
Switching varieties or herbicide systems from year to year doesn’t ensure blackleg resistance, Eadie cautioned. Plant science companies may have proprietary resistance genes but they also share biotechnology.
“There are a lot of public sources of blackleg resistance that all companies have access to.”
For Peng, understanding both sides of the game — nature and biotechnology — is the key to canola sustainability. Peng and other blackleg experts have initiated a project to determine all the resistance genes in existing commercial varieties.
He has also applied to the appropriate funding bodies in Manitoba, Saskatchewan and Alberta for a prairie-wide project to monitor the new races of blackleg and the race dynamics of the pathogen.
“If we have both of those pictures put together, we may be able to make some recommendations,” he said. “(Such as) some cultivar may not stand up to certain races in a (region).”
That means producers in that region may have to rotate to another canola variety or growers may have to walk away from the blackjack table and grow canola on a three year rotation.