Flea beetles pose one of the greatest risks to yields for canola growers in Western Canada.
A 2022 survey conducted on behalf of the Canola Council of Canada bore that out. Some 91 per cent of growers who participated in the survey identified flea beetles as the greatest economic risk to their crops.
That’s likely to remain the case in the coming growing season, an agronomy specialist with the canola council said during a presentation at Manitoba Ag Days in Brandon.
Chris Manchur says that’s why it’s so important for growers to be proactive in dealing with these yield robbers.
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“Overall, there’s just a lot of stress, whether that’s to the plant in that very vulnerable stage of the cotyledon or even on growers and agronomists having to go out and scout for this on a daily or twice-daily basis,” he says.
“Being able to figure out ways we can actually manage this (problem) effectively lowers that stress for everybody and ensures that those plants can actually get to that critical stage where we’re not sacrificing any yield.”
Preparing for flea beetle pressure can be difficult, Manchur acknowledges, since growers don’t know in advance where the pests might appear or how intense their pressure will be. Still, he says growers can take steps to mitigate the damage.
Perhaps one of the easiest and most effective options is to adjust seeding practices. A study at the University of Manitoba looked at three different plant stands (three, six and 12 plants per square foot) and the impacts they have on yields. The results indicated six plants per square foot should be the target, even in cases with significant flea beetle pressure.
Growers may want to slightly increase their seeding rates if they anticipate infestation.
They might also consider seeding into a warm, moist seedbed to promote strong stand establishment and speedy seedling growth, which will help the crop outgrow the susceptible stage sooner.
“When we’re taking a look at seeding that canola down, maybe it isn’t going to be that first crop that you put into the ground, especially if those soils are cold,” Manchur says.
“That is contrary to some management strategies where you want to seed earlier to get your longer growing window. It’s really about finding that balance and assessing your risk on what’s going to be your yield robber. Is it the length of your growing season or is it that intense flea beetle pressure?”
Seed treatments can help growers deal with flea beetles, Manchur explains. He cited recent work by researchers at the Agriculture and Agri-Food Canada research facility in Saskatoon that showed untreated seed can be “devastated” by flea beetles.
In some cases, growers should consider an upgraded seed treatment rather than a base treatment.
“In many cases, having an upgraded seed treatment is really going to help,” Manchur says.
“This past growing season we saw many cases where the difference between a base seed treatment and an upgraded one was night and day. It could only mean two or three days difference in growth, but when you get to the end of the season, that can make a world of difference in terms of yield as well as timing and maturity.”
It’s important to remember seed treatments are typically effective for only three or four weeks after seeding, he says, and begin to downgrade once seed comes in contact with soil.
Sclerotinia stem rot
Sclerotinia stem rot is another common yield robber in canola. Incidence on the Prairies has dropped in recent years due to dry conditions, but it remains a real threat.
To combat that threat, Manchur suggests farmers stretch their crop rotation. A tight rotation combined with high infection rates allows sclerotia fungal bodies that are hiding in stubble to more easily return to the soil.
“That can be a causal agent for future years. (But) if you spread out your rotation a bit, you’re going to be reducing the amount of inoculum in your soil … and that rate of infection is going to be reduced a bit,” he says.
Several registered fungicides are available to manage the disease and there is no evidence to suggest any will be lost due to resistance.
Verticillium stripe
Canola council agronomy specialist Courtney Ross says verticillium stripe and blackleg are two pathogens on the radar.
“Verticillium and blackleg are very quickly giving sclerotinia a run for its money when it comes to our biggest yield robbers,” Ross told audience members at Ag Days.
Verticillium stripe was first detected in Manitoba just outside of Winnipeg in 2014. A 2018 study showed it was prevalent in eight per cent of fields in the province. That number climbed to 38 per cent in 2022 in a survey of 130 Manitoba fields. Its presence in Saskatchewan has also continued to grow.
Verticillium stripe is not picky when it comes to weather conditions, which has contributed to its rise, Ross says. It requires moist conditions in spring, which are common in Manitoba. It then needs hot, dry conditions around flowering.
Although there are no foliar or seed treatments registered for verticillium stripe, some basic agronomic practices can help manage it.
One of the most effective is to increase rotations, which can be “huge in breaking that disease cycle,” Ross says.
Another is to eliminate weedy hosts such as volunteer canola and wild mustard, which can be breeding grounds for verticillium stripe.
“Eliminating them from the field is so important,” she says. “Even if you do have a three- or four-year rotation, if you have a big patch of volunteers in those years between canola crops, we’re really not breaking the disease cycle all that much. We’re still creating an environment where the disease can breed and continue to inoculate that field. It’s really important to stay on top of those weeds.”
Ross says it’s also important to test, so growers know what they are dealing with and don’t mistake it for something else. She also warns growers to be suspicious of anyone claiming they have a solution to deal with the soil-borne disease.
“Be very aware there is not a solution at this time. If you see an advertisement of somebody saying we’ve got the cure for verticillium, I would proceed with caution.
“We want to make sure we are using products that are registered, that we know for a fact are going to be helpful for verticillium and at this time there are none.”
Blackleg can be particularly challenging to deal with, since it can survive on soil residue for at least two years. One of the most common symptoms of blackleg is stem cankering, which can lead to major yield loss.
Ross says it’s important to regularly scout fields for blackleg. The best times are prior to planting, at the vegetative state (cotyledon to two-leaf and three- to six-leaf), and at swathing.
“There’s no time like the present to start scouting. As soon as there are plants out there popping up and you’re out there looking for flea beetles, you can be out there looking for blackleg too,” she says.
As with verticillium stripe, increasing rotations and controlling weeds are critical in managing blackleg. Foliar fungicides and seed treatments can’t stop a blackleg infection if it’s already occurred, but they can prevent spread and reduce the chance of further infection down the road.
Ross also advises growers to consult their seed providers about getting the best bang for their buck in terms of genetics and trait stacking in hybrids. Take a close look at cultivars that offer genetic resistance, she says, and practice resistance stewardship by rotating cultivars.
“If we’re using those resistant cultivars, we need to make sure we’re practicing resistance stewardship and rotating our cultivars to make sure we’re doing our due diligence when it comes to combating genetic resistance like we do when it comes to managing our herbicide resistance.”
Dishonourable mentions
Several other pathogens bear watching, Ross says.
Powdery mildew doesn’t normally result in yield loss — but it can gum up equipment and slow efforts at harvest time. There was a higher-than-usual number of cases in Manitoba and Saskatchewan in 2023, and that scenario could play out again this year, Ross warns.
There was also a higher-than-usual number of cases of sooty mould on the Prairies last summer. It usually occurs late in the season in dry years.
Ross says it’s generally not worth spraying for sooty mould, since there is little yield loss associated with it and it’s often too late to spray once symptoms become visible.
Finally, if the sound of crickets drove you crazy last summer, you weren’t alone.
Crickets are generalists, which means they’ll feed on most types of crops, but don’t pose much yield risk. Ross’s advice is to limit spraying to headlands, since that is where they typically congregate.
