Verticillium stripe has become more prevalent in canola and is not easy to recognize because symptoms mimic other diseases like blackleg or sclerotinia. It’s important for farmers to familiarize themselves with the disease, as it’s expected to become a greater issue moving forward.

WHY IT MATTERS: Tracking historical trends in crop diseases in Alberta can give farmers a head start in preventative measures for present growing seasons.

“It’s here, and it’s going to get worse,” said Michael Harding, crop assurance program lead at Alberta Agriculture and Irrigation, in his disease update for 2025 at the Irrigated Crop Production Update in Lethbridge, Alta.

Segwaying into stripe rust, it has a hard time surviving in open conditions with little snow cover paired with cold temperatures. But, Mother Nature has a way of changing her mind.

“Based on the forecast, I don’t think we’re going to have a lot of stripe rust overwintering in southern Alberta. But, anywhere that there’s snow pack and mild winter conditions, it could survive. So we should keep an eye out for it showing up, and if it shows up early, it could be a real problem, especially in susceptible cultivars,” said Harding.

A dedicated head survey in 2025 showed out of 287 wheat fields processed so far, 28 tested positive for ergot, with the near 10 per cent ratio high compared to previous years.

In one sample, 1.4 per cent of the grain by weight consisted of ergot bodies, indicating a severe problem in that field.

“That is horrible. That sample was a 580 gram sample, and it had over 500 ergot bodies in it. So ergot was a real problem in some fields this year,” said Harding.

The survey is ongoing, with about 300 out of 450 total fields for wheat and barley processed. The final results will be released when the analysis is complete.

“That’s a lot of ergot bodies that are getting returned to the soil at harvest. So there could be some fields that have a lot of ergot. You don’t want to grow an ergot susceptible crop in a field that had lots of it in 2025,” said Harding.

For pulse growers of lentils and peas, if you are seeing root rot and it is getting worse, he recommended finding out if you are dealing with aphanomyces or fusarium or both.

“You are going to march to the drum of the aphanomyces. If it is there, you need to manage the field. When you do that you will also be managing fusarium, so it’s a good idea to do testing,” said Harding.

In 2025, 395 canola fields in Alberta were visited, striving for one per cent of canola acres in every county. There were 98 per cent which showed black-leg symptoms, with 44 per cent of plants affected.

Clubroot was found in eight per cent of fields and two per cent of plants. Sclerotinia affected almost half the fields and eight per cent of plants. Verticillium was minimal at just under one per cent in fields and only a few positive plants.

Zooming the microscope tighter to southern Alberta where irrigated crops are most common, the scouting area featured 90 fields. Black leg was more prominent in southern Alberta fields, but less sclerotinia to go with no club root or verticillium being found in southern Alberta fields.

“We do have irrigated fields in southern Alberta that have club root (historically), but not that many, and it’s really not spreading nearly as quickly in southern Alberta as it is in the other parts of the province,” said Harding.

About 95 per cent of 250 wheat fields surveyed in Alberta in 2025 showed some leaf spot symptoms and 35 per cent of the plants. On average, around 11 per cent of the flag leaf area was covered by leaf spot, with Harding noting some fields had much higher severity.

Stripe rust was found in 5.6 per cent of fields during the initial survey shortly after heading, but spread to 50 per cent of fields in southern Alberta by August.

“When striped rust shows up, it can spread really quickly. We went back about three weeks after this survey and looked at the same fields. The cultivars that had good resistance, you barely can find the stripe and then the susceptible varieties, some of them were devastated by this disease. But, it did show up late enough that it in lot of fields, it wasn’t that big of an issue,” said Harding.

Powdery mildew, wheat streak mosaic and bacterial leaf streak were also observed, with wheat streak mosaic found in just over eight per cent and bacterial leaf streak in four per cent of fields.

The prevalence of these diseases was similar in southern Alberta, though the severity (per cent diseased flag leaf area) was almost half that of the provincial average.

In historical disease trends, the most commonly-occurring disease in canola is black leg, followed by sclerotinia.

“In some years, that’s the second most common. In some years, it’s almost the least common depending on how much rainfall we get, usually around July,” said Harding.

In wheat, fungal leaf spots such as tan spot and septoria are by far the most common. Bacterial leaf streak and wheat streak mosaic have also appeared prominently in some years.

In barley, fungal leaf spots including scald and net blotch are consistently the most widespread. Loose smut and stripe rust are also present.

In pulses, root rot is the most frequently found disease in both pea and lentil fields. Other diseases such as chocolate spot and Alternaria blight are notable in faba bean.

Fusarium has been present as the most consistently common disease in garlic, with Aster yellows and stem and bulb nematode rising in prominence more recently.

Harding encouraged farmers to use disease scouting cards, the Prairie Crop Disease Monitoring Network and the Canada Canola Council of Canada as resources to help battle crop-specific diseases.

The post A look at disease prevalence in Alberta crops in 2025 appeared first on Alberta Farmer Express.

The big four diseases right now are:

• blackleg

• verticillium stripe

• clubroot

• Sclerotinia

WHY IT MATTERS: Growers can sometimes ignore early signs of disease in their fields until it is too late.

“You tend to react fairly rapidly to insects, things that move and crawl and kind of get your attention, but diseases kind of sneak up on us,” said Gabert at Alberta Canola’s grower engagement meeting in Stony Plain, Alta., in November.

Gabert said he likes growers to have a good idea of what their canola looks like in the field, particularly at the end of the season, and get feedback on how their crop yielded.

Healthy canola stems should look clean and white, with no fungal or disease growth plugging them up.

He said the inside of the canola stand should look clean, green and healthy, and if it doesn’t look like that, then a grower may have a problem.

By pulling a canola stem, growers can check for all four major diseases.

“It takes five to 10 minutes in the field to give you a good idea of what you’re looking at,” Gabert said.

Last year was dry, and since there was no rain during harvest, growers are going into the winter dry.

“We’re coming into the year with some uncertainty, the same as the year we came out of,” he said.

Genetics and seed treatment can make a big difference in fighting disease and insects.

Gabert told growers at the meeting that their crop will talk to them, and they must be prepared to listen to it.

“But as I move into what I call the big four diseases, I just want to dwell on the fact that whether you can identify specific things is not important,” he said.

“The important thing that I convince you is to cut into those stems,” Gabert said.

This simple test will check for clubroot, blackleg and verticillium stripe.

Growers can take unhealthy canola to their seed retailer, who should be able to identify problems.

Blackleg

“The best way to get a bad blackleg infestation is to have a favourite variety and grow it about six times in the same field. Now chances are that’s a wheat-canola rotation and it’s taken you a dozen years, and your variety or hybrid probably changed in that time,” he said.

“A decade ago, we did have a couple varieties that lasted that long, and that tended to be where we saw blackleg infestations.”

“While our genetics are good, disease will find a find a way to get around genetics.”

Gabert said fields with blackleg problems have stubble pieces with little black peppery spots on them. These are spore bodies that throw up spores for blackleg to infest the next crop. The best time to look for blackleg is after swathing or straight cutting.

There have been a few genetically resistant varieties of canola for blackleg, but resistance has broken down over the years. Growers with blackleg problems should change their resistance groups. If a grower picks a variety with the same or weaker blackleg resistance package, they should be aware that blackleg can cause a big yield loss.

“Farmers don’t use this tool very often, but you can take those same stubble pieces that you’ve been cutting and looking at and see if they’re clean. If they’re not clean, collect up a dozen of them and send them to someplace like 20/20 Seed Labs and they will resistance test them and tell you what race of blackleg is infecting those plants,” he said.

To scout for blackleg, growers should cut at the junction of the root in the stem and look for clean white tissue. Gabert said he cuts two-and-a-half inches lower than he used to for blackleg.

Blackleg is an airborne disease.

Verticillium stripe

Verticillium stripe, a relatively new disease, is a soil-borne disease caused by microsclerotia that live in the soil and plug the stem of the canola.

The disease has significant symptoms. There is shredding almost like Sclerotinia on the stem, black peppery microsclerotia and microspore bodies that carry the disease forward in the soil. The soil will look bleached and ugly.

“It’s been around about 10 years, really taking a bite out of Manitoba’s canola yields,” Gabert said.

However, he hasn’t seen severe symptoms of the disease in Alberta. In Manitoba, growers have found disease can take away about 20 per cent of their yield.

He said the best way to manage verticillium stripe disease is to manage blackleg aggressively, because both diseases do similar things in the stem. When the two diseases are found at the same time, the impact is more pronounced.

A little verticillium stripe will not have the same impact on canola if blackleg is not present.

Verticillium stripe discolours the stem, plugs the xylem and inhibits the transport of nutrients and water in the stem of the canola. Verticillium stripe grows from the bottom up, so it’s a good idea to cut two inches into the root.

“Sometimes you’ll find that gray fungal growth or evidence of some plugging further down in the roots than you normally would for blackleg,” he said.

“It’s easy to do the two. The take home message is you’re looking for clean white tissue in the root.”

Verticillium stripe plugs much less than blackleg. When it plugs the stem, it appears in more of a starburst pattern.

“If you’re really lucky and you start cutting in the roots far down, you can actually follow which root brought it into the main stem,” he said.

Clubroot

Clubroot is still a problem, and scouting for it is best done after swathing. It doesn’t take many spores to cause a clubroot infection.

“You’ll probably have both white galls and some brown, older, mature galls that look like peatmoss falling off,” he said.

“If you don’t have roots on your canola that look normal, and maybe you’ve lost some of the root hairs when you pull them up, there’s a good chance that clubroot has digested or used or abused some of those roots.”

If clubroot is in a root, it will hijack the system, make its own home and widen portions of the roots further down.

Gabert said growers should get down on the ground and pull canola stems to check for clubroot, rather than assuming a field is bad once damage can be seen from the truck.

“By the time it’s thinned out, and visibly wilting on a hot summer day, you’ve got a lot of galls and lots of seed and a lot of spores,” he said.

There are a few weedy relatives of canola like shepherd’s purse and stink weed that are susceptible and can carry clubroot. Many Chinese vegetables like Chinese cabbages, bok choy and gai lan (Chinese broccoli) are brassicas and can also get clubroot. They are commonly grown around the world.

Gabert said the take-home message for clubroot is to keep it low and local. Seed spore on the fields should be kept low, and there should be at least a two-year break between canola varieties. Ninety per cent of the spores or seed for clubroot die in that first two years.

“If you’re on a one-in-three rotation, only 10 per cent of those spores will still be available. If you’re at a relatively low clubroot infestation and 90 per cent of those spores die, that’s not a lot of pressure for the genetics to try to deal with in your field. If you’re in a dead spot, and 90 per cent of way too many clubroot spores die, you probably still have way too many spores in those patches, if that’s the case. That will be some significant pressure on those resistance genetics that you use,” he said.

Gabert encouraged growers to manage the resistance available in seed varieties, and don’t let clubroot take over.

Patch management also helps.

If a grower finds a clubroot patch about the size of a large table in their resistant variety, they should go into the patch, pull out roots, toss the plants in a garbage bag and send it off to a landfill. That will get rid of a lot of spores in a hurry.

Having grass in the entry way to a field can also cut down on clubroot establishment, he said.

Sclerotinia

Gabert said many people feel sclerotinia is not a problem, when in fact, it’s still a big problem.

“I would like to think that this is a disease that can take the top end off a good crop,” he said.

“If you’ve got a yield potential of 40 bushels or more and a crop canopy that can stay wet, chances are that Sclerotinia can be an issue. It’s one of those break-even propositions most of the time.”

Frequently, when producers spray for Sclerotinia, they will get the cost of their fungicide and application back.

“You’re not going to be too excited about spending that much time in the sprayer. But on the odd year, especially when we used to swath, you’ll find big batches of sections of the field that just go poof. The stems have been digested. The seed hasn’t set in there. And you’ll pay for three to four years of application or maybe more in that single year,” Gabert said.

“Managing sclerotinia aggressively is important in my books, relatively simple, and we do have some good genetic tolerance from at least one of our seed suppliers.”

Gabert said additional information about diseases is available from the Alberta Canola Producers Commission. The Canola Council of Canada has a newsletter called Canola Watch that is a good source of information for producers.

The post Scouting for disease in canola crops appeared first on Alberta Farmer Express.

The headline was a bit sensational, but it did reflect the thinking at the time. Scientists, agronomists and canola growers were extremely worried that clubroot would spread across the Prairies and devastate Canada’s canola industry.

The paranoia about clubroot wasn’t short term.

It lasted from 2003, when the first case of the soil-borne disease was found near Edmonton, to the middle of the 2010s.

Stephen Strelkov, a University of Alberta plant pathologist, was a key player in the research to understand the disease, which causes swellings or galls to form on the roots of canola plants.

A severe clubroot infection in part of a canola field can cause a 100 per cent yield loss.

Like many others, Strelkov was very concerned about clubroot and what it could mean for canola production.

“Fifteen years ago it was like, “Oh my God, what’s going to happen, is this going to be a … major issue’? ” Strelkov said from his office in Edmonton.

“When the first cases were detected on canola in Saskatchewan and Manitoba, that maybe we might have a similar scenario (to central Alberta).”

Autumn Barnes, research manager with Alberta Canola, remembers the event that prompted the Western Producer article and its eye-catching headline.

It was a clubroot disease meeting in Brooks, Alta., during the summer of 2013.

“At that time, our only ‘real’ management option was sanitation, and there were a couple varieties with limited resistance available for farmers in central Alberta,” Barnes said.

Nowadays, 12 years after that headline, the situation has completely changed. Clubroot has become a manageable risk and something that’s almost invisible in Saskatchewan and Manitoba.

“As in 2023 and 2024, no new visible clubroot symptoms were recorded via the clubroot monitoring program in 2025,” said a preliminary canola disease survey for Saskatchewan, published this fall.

In Manitoba, no symptoms were found on canola plants in a disease survey of 117 fields in 2025.

The lack of detections suggests that clubroot is not a massive problem in Western Canada.

“It’s not the same huge risk that we were thinking, 15 years ago,” Strelkov said.

What happened?

After the initial detection of clubroot near Edmonton, it became clear that the problem was much larger than one field. Symptoms of the disease were soon found in hundreds of Alberta’s canola fields.

By 2007, several Alberta counties had restricted the growing of canola on infected fields.

In Leduc County, canola was permitted once every five years to control the spread of clubroot.

Outside of Alberta, clubroot spores were found in Saskatchewan in 2008 and one year later in Manitoba.

There were worries that clubroot couldn’t be contained and Prairie farmers would have to grow canola on a longer rotation to keep the disease in check.

However, farmers, agronomists, scientists and canola seed companies responded in a co-ordinated effort to tackle the risk.

A combination of factors made a difference:

• The gap in time between detections in Alberta and other provinces.
• Pioneer Hi-Bred developed a clubroot resistant canola hybrid that hit the market in 2009 and 2010.
• Farmer awareness — growers became more vigilant about sanitizing equipment and moving machinery to prevent the spread of clubroot infected soil from field to field.
• Government investment in equipment to detect clubroot DNA in the soil before the disease became a problem.

These factors and other actions helped prevent the buildup of clubroot spores in new fields across the Prairies.

“Much earlier ability to recognize the symptoms and take preventative measures,” Strelkov said, noting farmers in Saskatchewan and Manitoba began seeding clubroot resistant varieties in the absence of clubroot.

“(If) you’re starting to grow resistant varieties, pre-emptively, that makes it a lot more difficult for the pathogen to build up.”

For Barnes, the crucial bit was a targeted investment in clubroot research. Grower groups such as Alberta Canola invested to identify resistant traits, which led to commercial varieties with a diversity of resistant genes.

“It is incredible to think that virtually every commercial canola variety available in the Prairies (now) has some type of clubroot resistance package,” she said.

“In addition to genetic resistance, funders across the Prairies have leveraged resources to understand clubroot pathotypes, options for management (such as liming), testing and general disease biology.”

The clubroot pathogen does prefer acidic soil, which led to the theory that the disease is less problematic in Saskatchewan and Manitoba because low pH soil is less common in those geographies.

That theory is somewhat true and somewhat false, Strelkov said.

Clubroot spores do better in acidic soils, but the disease can take hold and cause damage in neutral or higher pH soils.

“If your soils are acidic, you’re at more risk,” he said.

“(But) given the right conditions and short rotations, clubroot can become an issue in fields that wasn’t as acidic.”

Canola with clubroot symptoms is rarely detected in Manitoba or Saskatchewan disease surveys, but the disease is still top of mind for canola growers in parts of Alberta.

More than 4,300 canola fields in the province have had symptoms of clubroot on canola plants. In the other Prairie provinces, the total is 127.

Plus, soil samples in Alberta have detected millions of spores in one gram of soil and new pathotypes of clubroot have appeared.

That’s concerning, but early detection allows the canola industry to identify the new variants before they run wild.

Canola is still grown in areas with a history of clubroot infections, and average yields in Alberta were nearly 43 bushels per acre in 2025, close to historical highs.

That’s an incredible success story, considering the clubroot fears during the 2000s in Alberta.

“In 2003, 2004, 2005, we were thinking, ‘Will we be able to grow canola, beyond once every seven years’?” Strelkov said.

“So, even here, it’s being managed quite well. … If we do our work and stay ahead of it, I do think it’s a very manageable problem.”

The post Canola’s clubroot success story appeared first on Alberta Farmer Express.

These “hot spots” included the counties of Leduc, Parkland, Sturgeon, Strathcona and Camrose — all areas with a consistent history of clubroot.

However, the disease of canola was found in more moderate numbers as far north as Clear Hills and Northern Sunrise and as far south as Newell, said Kendra Reimert, agronomy specialist with the Canola Council of Canada, emphasizing the numbers are based on incidence rather than severity.

“When they’re checking these fields, they are just looking to see if the clubroot is present in that field or not. So when we’re seeing those hot spots that would just be based off of the cumulative number of infected fields,” she said.

A 2024 province-wide survey by the University of Alberta and Government of Alberta identified clubroot in 47 counties and 307 canola crops throughout the province.

A total of 691 fields were surveyed. Of those, 167 cases of clubroot were found in fields with no prior history of the disease, according to data provided by Stephen Strelkov and colleagues at UAlberta.

So what does that mean for the crop disease in 2025? Not much, said Reimert. Clubroot is highly dependent on environmental conditions that are impossible to predict.

“Typically clubroot prefers those wet conditions early on in the spring and then wet conditions in the fall as well to have that spore population show up for the following year.”

Although parts of Alberta received significant moisture in the spring, particularly on its northeastern side, Reimert said wet conditions in the fall were hit-and-miss with conditions trending towards the dry side.

“So at this point, it would be too early to tell and dependent on the grower’s best management practices. If they’re working with genetic resistance, sometimes that clubroot can be undetectable in some fields, even if we do have those environmental conditions.”

Producers that had clubroot — which has no chemical controls — in 2024 likely still have it thanks to its tendency to overwinter as resting spores, said Reimert. However, that opens an opportunity for mindful crop rotation decisions in the coming growing season.

“Select a host that’s not susceptible, whether that’s cereals, peas — anything basically but canola — and manage your volunteers if you have any volunteer canola or any other type of susceptible host — which can include weeds such as stinkweed — to make sure that those are managed properly and limit that spore load increase in the following year.”

The most reliable way to confirm clubroot, said Reimert, is to pull plants and look for galls.

Clubroot DNA can also be found by lab-testing soil and plants at select laboratories throughout western Canada, but the variability and “patchiness” of clubroot make it difficult to determine the spore load — a key measurement of disease severity — across a field.

“Many labs offer a detection (PCR) test on whether clubroot is detected in the sample or not.

“The other test is a quantitative detection test (qPCR) which will provide the number of spores per gram of soil. Variability of clubroot in the soil, sample size, location, number of cores and handling samples can influence these results.”

Severe clubroot infections will often present themselves through dead canola patches in wet environmental conditions, said Reimert.

Keep spore counts low

The all-important priority in clubroot management is to keep spore counts low, said Reimert. This can be done by attending to several best management practices:

To the surprise of few, frequent scouting for clubroot is essential. High-traffic and moisture-prone areas are particularly vulnerable to the pathogen and require diligent scouting, said Reimert.

High-traffic areas can include entryways while moisture-prone areas can include field depressions or fields that are typically more wet than others.

Reimert emphasized sticking to a minimum two-year break between canola crops.

“If it is high severity, the longer the rotation the better. But we understand that the grower may be limited in their rotations, so just be mindful of that one- in three-year rotation at a minimum.”

Growing clubroot-resistant canola varieties on every acre of the field is one of the most effective ways to manage clubroot, said Reimert.

“It’s really important for growers just to be mindful, when they’re selecting their seed for the following year, that they do have clubroot resistance built into it. Have a good conversation either with your retailer or agronomist if testing should be done to identify if clubroot is present and (its) severity and which varieties to select.

“This can give the grower better insight on which varieties to select for the upcoming year.”

New canola varieties are regularly listed on the Canola Council of Canada website clubroot.ca. It includes an overview of the clubroot disease cycle, how to identify clubroot disease and a section on the disease testing available.

A table listing all the clubroot-resistant canola cultivars registered for use in Canada can be found at canolacouncil.org. Enter #current-canola-cultivar-trait-labels in the search bar, scroll down to “canola cultivar traits” and hit “Read More” to access the table,

Finally, controlling susceptible weeds such as stinkweed can help minimize clubroot spore release and gall formation on canola plants, said Reimert.

Keep it local

Making sure the soilborne disease stays away from clubroot-free fields — both your own and your neighbours’ — is the second category of clubroot management. Reimert suggests reducing tillage if possible to reduce the spread of soil and a few other key management practices.

Clean equipment using proper sanitation techniques when moving from field to field, she said. However, depending on its size, cleaning equipment can be time-consuming. In cases where time is of the essence, Reimert recommends cleaning at least the the visible clumps of dirt and debris between fields.

Some equipment sanitation techniques include rough cleaning of the equipment by scraping off visible, loose dirt on openers, tires, wheels and frames; pressure washing to remove remaining dirt; using a disinfectant such as a one per cent bleach solution (only effective after the majority of soil and debris has been removed); and saving any tillage in clubroot-infected fields for last. Also, limit working fields when they are wet to prevent excess movement of soil.

Clubroot rarely infects an entire field. Instead, it tends to cluster in patches, and you can manage those.

“So from a patch management perspective, stake out those infested areas to avoid traffic in those areas where you know clubroot is already there, control the host weeds in that patch with herbicide management and just make sure (canola plants) aren’t going to seed or have galls form on them.”

Although it has been found in alkaline soils as well, clubroot tends to favour acidic soils. Hydrated lime can be used to gain soil alkalinity.

“There has been some research done in those highly acidic soils that (show) you can apply lime until that soil pH reaches around 7.2 to 7.3 to reduce the gall formation on some of the canola varieties,” said Reimert.

If all else fails, seeding an infested patch to grass may help minimize the soil movement that spreads the pathogen.

“You can break up that grass and crop that area again once the spore loads are lowered based on annual soil testing, but … how long that grass is seeded down for will depend on the level of infestation.”

The post Big clubroot numbers urge new vigilance appeared first on Alberta Farmer Express.

Reports out of Europe suggest the fungal disease could cause losses of 10 to 50 percent on oilseed rape. However, extreme losses are usually confined to a small number of fields in England and northern Europe.

University of Alberta scientists will soon publish a Canadian estimate to nail down what verticillium means for yield.

“We were the ones who gave the blackleg yield loss model … and the clubroot yield loss model,” said Sheau-Fang Hwang, a plant pathologist with the U of A. “So, everyone expects we will … (provide) the verticillium yield loss model.”

Hwang and her colleagues hoped to release their results this year, but publication will be delayed until 2024.

Verticillium stripe is a relatively new disease for canola growers in Western Canada. It was first discovered in 2014 near Winnipeg.

The fungus, Verticillium longisporum, infects canola and produces tiny, pepper-like sclerotia on or inside the stem of the plant. The sclerotia fall on the soil and into crop stubble after harvest. The small particles move with wind and water to other locations. Farmers can also pick up the fungus on their equipment and boots and transport it to other fields.

The infection interferes with the uptake of water and nutrients. Symptoms include early ripening, plant stunting and leaf chlorosis and shredding or striping of the stem tissue. The symptoms usually appear later in the growing season.

“Looking for verticillium, you have to slough off that outer stem wall … to reveal the micro-sclerotia. That’s a really key (part) of diagnosis,” said Justine Cornelsen, agronomic and regulatory services manager with BrettYoung Seeds and a former agronomist with the Canola Council of Canada.

On the Prairies, verticillium is most common in Manitoba, where it appeared in 40 percent of canola fields in 2022.

“In Manitoba, we don’t talk much about clubroot. We talk about verticillium,” said Cornelsen, who lives near Virden, Man.

The disease is also spreading across Saskatchewan. It was detected in dozens of eastern Saskatchewan fields in 2022 and in other regions this summer.

Earlier this year, Hwang authored a paper saying verticillium is a significant threat to canola production in Canada. When verticillium and blackleg are present in the same field, the two fungal diseases seem to join forces.

“(When) inoculated together in field and greenhouse experiments, blackleg severity and yield losses increased relative to when (the blackleg pathogen) was applied on its own. The severity of verticillium stripe also tended to increase,” says the 2023 paper, published in Plants.

“The results suggest that the interaction between (blackleg and verticillium) may cause more severe losses in canola.”

Cornelsen has been keeping a close eye on verticillium since it first appeared in Manitoba a decade ago.

She’s learned that some of the normal rules for crop diseases don’t apply to verticillium.

For one, verticillium thrives in hot and dry conditions. Most diseases prefer hot and humid.

“Once it gets into the plant (under) those hot and dry conditions … that pathogen is growing up through the vascular system,” she said.

“When you don’t have a bunch of rainfall, it’s able to move (through the plant) and make the symptoms more severe.”

Rain and excess moisture seem to prevent verticillium damage to canola plants.

It’s possible that crop scouts have failed to detect verticillium in the past because its symptoms are more noticeable just before or after harvest.

“That 60 per cent seed colour change, (the) typical timing for disease survey, isn’t the right timing to look for verticillium,” Cornelsen said. “It’s likely, for years, been misdiagnosed as something like blackleg.”

However, it appears that some canola varieties do have resistance to the disease.

University of Manitoba researchers have found that hybrids — in the market or in the development pipeline — are resistant or moderately resistant.

Some seed companies now promote certain hybrids in their lineup as having some degree of resistance to verticillium.

Genetic resistance in commercial canola hybrids could be preventing “drastic” yield losses at the field level in Western Canada, Cornelsen said.

– Robert Arnason is a reporter for The Western Producer.

The post Researchers study verticillium yield losses appeared first on Alberta Farmer Express.

An effective fight against the soil-borne, canola-targeting disease requires several solutions and fall is the time to think about them.

“Because clubroot is such a complex disease, it’s really important that we acknowledge that it will need a complex solution to manage it,” said Marissa Robitaille Balog, an Agronomy Specialist with the Canola Council of Canada.

“(Resistant varieties) are not a fix-all solution, so we need to be stewarding them carefully to make sure that we have them available for the long term, which is why scouting for disease presence or resistance breakdown is so important.”

Clubroot is a disease of cruciferous plants. Its galls tie up nutrients and in extreme cases will prevent canola roots from delivering sufficient water and nutrients to the plants.

When it arrived in Alberta two decades ago, clubroot quickly found a home in acidic central Alberta soil where it thrives, said Tom Ernst, a researcher with Corteva Agriscience.

“If you look at the Edmonton area where it was first found, you get slightly more acidic soils than, say, further down south. That helps facilitate the establishment of the disease.”

However, producers who grow canola in alkaline soil shouldn’t be complacent. The disease has mutated, said Ernst, so different strains of clubroot can affect those soils as well.

“People hypothesized that it’s not spreading down (south) or maybe our soil pH is high enough that we’re going to avoid getting it. And it’s not exactly the case.

“We’re finding there’s enough diversity in clubroot that there are pathotypes that will infect crops in higher pH situations.”

Fall is an excellent time to scout for the disease, he said.

“If you come into an area of your field that has lower yields and it’s confusing, why not get out and pull some plants? If you pull a plant and it has galls, then you know it’s there. If you know where it is, that helps you manage it a little bit better. You can avoid those areas, maybe work them last in the process of planting next year.”

Robitaille recommended scouting multiple parts of the field, not just the field entrance.

“If your field has multiple entrances, really focus on those high traffic areas or areas that are really prone to moisture, keeping an eye out throughout the growing season for any prematurely dying patches that may be susceptible to clubroot.”

Post-harvest is also ideal for soil sampling. If galls are found while scouting, the next step should be a soil test, said Robitaille.

“We highly suggest soil testing to determine if there is clubroot DNA present.”

Sampling is also a key tool to check whether spore loads are low enough for seeding canola the year after planting a non-canola crop. Wheat, for example, can’t spread clubroot but the movement of soil with equipment can carry it.

“You’ll want to check to see if your spore loads are low enough by collecting soil samples after harvest and seeing if it’s up to standards to go into canola cultivation in the following year,” said Ernst.  

Some producers use soil amendments or liming to raise soil pH so it’s less susceptible to clubroot, but those can be expensive options, he said.

“None of that’s really taken off on any large scale. It’s a little bit cost-prohibitive.”

Controlling clubroot doesn’t work in a vacuum, said Robitaille.

“Controlling fall weeds that may possibly serve as a host for a clubroot pathogen is important.”

Much of fall/winter clubroot management will be done around the kitchen table, strategizing for the coming growing season. One of those considerations may be the painful — but ultimately beneficial — decision to not plant canola in clubroot-infected fields for two years.

“The recommendation of a two-year break between growing canola can’t be understated in terms of its effectiveness,” said Ernst.

“Field-based data from Alberta shows that if you can extend your rotation from a one-in-two to a one-in-three canola rotation, you can help bring down the clubroot resting spore load in the field by about 90 per cent.”

Virtually all canola growers recognize the value of rotating crops, but what about rotating canola varieties or genetics? This has become a recommended practice as well, said Robitaille.

“If you’re growing a resistant variety and you’re seeing breakdown happening in the field, that’s an indication that you need to be switching genetics,” she said.

“Pathotypes in the field are often diverse and there can be multiple pathotypes present at once. As populations become more diverse and we’re able to breed more clubroot resistant genes and varieties, the usefulness of rotating different varieties will definitely increase.”

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Results Driven Agriculture Research, the Alberta Canola Producers Commission and the Saskatchewan Canola Development Commission have awarded $1.25 million to Stephen Strelkov at the University of Alberta to lead an expert team in:

• breeding resistance into new crop varieties; 
• developing new ways to control the pathogen; and
• identifying clubroot resistance genes.

As part of the five-year project, the team is expected to contribute to the sustainable long-term control of clubroot and improved resistance stewardship, helping producers manage and reduce clubroot spores that contaminate their fields. Clubroot can make infected land less desirable to some buyers and renters.

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They identified 25 unique clubroot pathotypes from samples collected from more than 250 fields in Alberta, Saskatchewan and Manitoba in 2019 and 2020. Seven of the strains are new, six of which can bypass the crop’s bred resistance against the disease. 

“The findings really underscore how quickly pathotype shifts are occurring and how quickly we are finding new pathotypes. And it is likely we will continue to find new ones,” study lead Keisha Hollman, a PhD candidate in plant science, said in a U of A release. 

Clubroot is caused by a parasite that infests field soil with resting spores that can survive up to 20 years. 

The release said most of the pathotypes were found in only a handful of fields, but the dis- ease’s ability to continue to emerge poses a challenge for canola producers. It can take up to a decade to develop a clubroot-resistant plant. 

Hollman said producers must continue to manage the risk through integrated management strategies that help take the pressure off genetic resistance alone. Those measures include sanitizing farm equipment between fields and rotating out of canola for at least two years — a strategy found in a 2019 U of A study to reduce the number of clubroot spores by about 90 per cent in field soil.

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When it happens, thank an AAFC research team in Saskatoon that has developed canola breeding lines that are highly resistant to almost all known clubroot races in Canada.

“This could revolutionize the race differentiation for the clubroot pathogen,” said an AAFC release.

“This is important because it will provide crop breeders and growers with information they can use when developing or growing cultivars with increased clubroot resistance.”

In the context of clubroot and other crop diseases, a “race” is a unique population in which all individuals carry the same combination of avirulent genes.

Profiling race structure in crop diseases isn’t new, said team leader Fengqun Yu. In fact it was developed 10 years ago to characterize the blackleg pathogen, another disease of canola.

“We are able to determine the race structure of the blackleg pathogen,” said Yu. “Our research wanted to catch up to the concept that’s widely used for blackleg.”

Basically, the researchers infect a canola gene to test its resistance to a given “race” of clubroot. It’s similar to another research method in which the clubroot pathogen is broken down into pathotypes.

This technology is somewhat different, said Yu. The team already has the clubroot-resistant line; the goal is to test how effective it is when tested against a range of clubroot races.

“Through race profiling we can predict the effectiveness of a resistant gene in a cultivar. So for example, the frequency of an avirulent gene in the clubroot pathogen is 50 per cent. That means that the corresponding resistance gene in the canola cultivar is an effective rate of 50 per cent,” she said.  

But this is just the tip of the iceberg. The team has been working on clubroot resistance since 2011 and recently developed a new mapping-by-sequencing method and a “pipeline” for gene identification that accelerates the development of genetic resources.

This has set the stage for the identification of more than 20 clubroot-resistant genes and markers, including the first such gene in black mustard and the first major resistant gene in Brassica oleracea, a plant species that includes cabbage, broccoli, cauliflower, kale, Brussels sprouts and other leafy green vegetables.

They have also developed molecular markers linked to each of these genes for use in molecular breeding as well as canola and mustard germplasms for resistance to clubroot that can be used by breeders.

Molecular breeding is genetic manipulation at the DNA molecular level intended to improve characteristics of interest in a plant or animal.

Finally, researchers found that when it comes to clubroot resistance in canola, two genes are better than one. This means two genes acting in unison could manifest broad spectrum resistance to Canada’s clubroot pathogens. And it seems to work through a mathematical mystery, said Yu.

“To give a simple example, with Gene 1 the clubroot infection rate is about 50 per cent. With Gene 2, the infection rate is 40 per cent. Neither gene is resistant to clubroot at all. But if we combine Gene 1 and Gene 2 together, we got 100 per cent resistance,” said Yu.

“So you might say in simple terms that one plus one equals more than two.”

Yu can’t overemphasize the importance of ongoing clubroot resistance in canola and other brassicas. Clubroot is one of the most serious diseases of brassicas because its spores can remain in the soil for up to 20 years.

According to the Alberta government, clubroot galls tie up soil nutrients so they can’t get to the plant. Severely infected canola also prevents transportation of water to the above-ground plant.

Clubroot rose to prominence on the Prairies about 20 years ago when canola acreage started to grow in central Alberta. Since then, it spread across the Prairies along with producers’ choice to grow canola, one of the most highly valued crops in western Canada.

Much like colds and flus in humans, clubroot spreads largely through contact. Producers’ sole initial defence included diligent crop rotations and equipment disinfection. 2009 saw the registration of the first clubroot-resistant canola cultivar in Canada.

Some of the genes identified by the Saskatoon team have been used by crop breeding companies for the second generation of clubroot resistance cultivars. Most of Yu’s recent work has focused on the third generation of clubroot resistance.

But it’s highly unlikely to end there. As with pests treated with chemical crop protection products, clubroot will continue to adapt to resistant cultivars.

“The pathogen population always evolves. There’s always something new,” she said.

It will probably take a few years for Yu and company’s technology to be incorporated in new, ready-to-plant varieties with more diverse clubroot resistance genes, but she doesn’t think it will take too long.

“The breeding companies are very actively trying to bring new cultivars to the market in the canola industry. To my understanding, I think there are at least two sources of (clubroot) resistance on the market already with more coming, and they’re coming with diversity.”

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Spot-treating soil with the mineral reduced the overall occurrence and severity of the disease by 35 to 91 per cent, growth experiments showed.

The finding, published in the Canadian Journal of Plant Pathology, could give farmers an option for managing clubroot, alongside current use of resistant varieties.

Lime has traditionally been used to manage clubroot in related plants, such as cabbages for market gardens, but not on a large scale in canola crops.

“Genetics are our first line of defence, but plant resistance can erode or break down, so we need to find every possible option to help control the clubroot pathogen in what is an important cash crop for Canada,” says researcher Nicole Fox.

As a non-genetic management practice, liming treatments could help combat all strains of clubroot in canola, adds Fox, who conducted the study to earn a Master of Science in plant biosystems from the Faculty of Agricultural, Life & Environmental Sciences.

Spot treatments could help control contaminated areas of a field or stem the spread of clubroot into a new field.

The lime works by neutralizing the highly acidic soil preferred by clubroot, reducing the likelihood of spore germination and plant infection.

One of the first studies to test hydrated lime in the field in Canada, the research also showed the product was more effective at managing clubroot in canola than granulated limestone, another form of lime more commonly used to treat agricultural soil.

Applying moderate to high amounts of the powdered lime resulted in canola plants that were still productive even if infected by clubroot. The plants also released fewer spores of the clubroot pathogen.

Lowering acidity levels also increases the soil’s general health, an important benefit to liming, considering Alberta has about one million acres of strongly acidic and 4.5 million acres of moderately acidic cropland soils, Fox notes.

But hydrated lime’s effectiveness does hinge on certain factors, like the interval between application and seeding, so it needs fine-tuning before it can become a practical tool, says U of A plant pathologist and study co-author Stephen Strelkov, who supervised the research.

“While lime showed good potential for clubroot management, the results varied. Sometimes the treatments provided very good control; other times they didn’t. So, we need further research to work out some details.”

Canola bred to be genetically resistant is still the most effective tool against clubroot, Strelkov adds, but options like hydrated lime could help improve the “durability of resistance and overall sustainability” of disease management.

“There may be situations, if the efficacy of lime is consistent and the costs of application reasonable, that it could be used on a larger scale.”

The research was funded by Agriculture and Agri-Food Canada, Canola Council of Canada, Alberta Canola, SaskCanola and the Manitoba Canola Growers via the Canadian Agricultural Partnership program. In-kind support was also received from the U of A and Alberta Agriculture, Forestry and Rural Economic Development.

Bev Betkowski is a communications associate for the University of Alberta.

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