The 4Rs revisited

According to Fertilizer Canada, programs for 4R nutrient stewardship — applying the right source at the right rate, right time and right place — balances the goals of farmers, industry and government to improve fertilizer efficiency, crop production and on-farm economics, while minimizing environmental concerns related to agriculture.

These principles can also be applied to disease management, said Turkington.

Apply the right tools, in the right place, at the right rate and at the right time for your best disease management outcomes.

Right tool

When selecting the right tool for disease management, farmers should consider what issues they face on their farms. In some cases, solutions will be field specific, said Turkington. For example, in the case of cereal rust, one of the best tools is host resistance.

“A good variety with a good level of resistance will mitigate pretty well all of the risk you have in terms of rust and its impact on yield,” said Turkington.

More recently, growers have been dealing with bacterial leaf spot and leaf streak issues in a variety of crops. In some cases, growers assumed they were dealing with a fungal leaf disease — something like tan spot or septoria in wheat or net blotch or scald in barley — when, in reality, they were dealing with a bacterial pathogen.

“Spraying a fungicide will have no effect whatsoever,” said Turkington.

Scouting is key to selecting the right tool.

“If you’re not actively out in that crop scouting what you have there … getting the symptoms confirmed in terms of what is causing those issues, you may look at using the wrong tool to try to mitigate that risk,” said Turkington.

Depending on the source of the disease, crop rotation as well as seed selection are two good mitigation strategies, he added.

Right place

Knowing where to look for disease is also crucial to proper management. For instance, those farmers focusing primarily on in-crop diseases may be missing the boat in terms of mitigating the risks associated with seed-borne diseases or seed health issues, said Turkington.

“There you may look at using a good seed treatment, good application technology and a product that is registered for the disease issues that you have,” he said.

Turkington suggested working with a seed testing lab to get a disease screen done on seed intended for planting. Doing so helps farmers prepare for potential disease issues. If there are very high levels of seed infection, the seed may be too compromised already in terms of germination and vigour, and growers may be better off looking at an alternative seed source, he advised.

Right rate and time

When it comes to selecting the right rate, the same principles used for fertilizer management can be applied to disease management strategies as well. In many cases, said Turkington, applying a reduced rate may actually compromise the level of control. This, in turn, can affect yield, quality and grade.

For example, Turkington referred to complex disease matters in wheat, where seedling issues, leaf disease and fusarium head blight may all be of concern. Both the right timing and the right rate are important here, as the crop advances through different growth stages.

“You might need to put a fungicide on to mitigate an emerging leaf disease issue or a rust issue like stripe rust,” said Turkington. “But then, you’ve also got to come back in and utilize a fungicide to get some suppression of fusarium head blight.”

Put it all together

In many cases, when it comes to disease pressure, growers will need a combination of tools. A prime example of this is fusarium head blight, which is caused by Fusarium graminearum. Relying on varietal disease resistance alone is not going to cut it, said Turkington. Neither is solely relying on fungicide applications or crop rotation.

“You need to look at a combination of strategies to mitigate that disease,” said Turkington. “That, often, is pretty difficult, even when you use multiple tools for fusarium head blight.”

Growers who want to get the most out of the tools they have — or will have — need to apply this foundational knowledge, Turkington said. This involves first gaining a complete understanding of the crop and crop diseases as well as the available tools to mitigate disease — then apply the right tools, in the right place, at the right rate and at the right time.

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Manitoba

As of recent years, soybean has become one of the more widely grown crops in Manitoba. Root and stem diseases are the main concern. Soybean is a relatively new crop to the province and, as such, disease pressure is still quite low.

Why it matters: New threats are emerging while the incidence and spread of established diseases continue. Understand what’s happening in your province to inform disease management decisions.

“But we are expecting it to develop as we continue to grow soybeans,” says Cassandra Tkachuk, production specialist, Manitoba Pulse and Soybean Growers. “We know that stem and root diseases can have the biggest impact on production and quality.”

Stem diseases such as sclerotinia root and stem rot haven’t been a real problem in soybeans in Manitoba yet, but the risk is greater for those who have tighter rotations of host crops. “It is also largely weather dependent,” adds Tkachuk. “Risk can be there across many years, but only expressed if conditions are ‘right,’ around the time of flowering.”

Northern stem canker is also starting to appear more often, she says.

Fusarium is the No. 1 root pathogen across all pulse crops, including soybeans. Fusarium is almost always present, but not always at high levels. An opportunistic pathogen, it will often set in when other diseases infect the plant.

Exclusive to soybeans, the pathogen Phytophthora has been making an appearance as well, although at very low levels in 2020. Like Aphanomyces, it likes and depends on wet environmental conditions.

There has been quite a jump in pea acres in Manitoba as of late, making aphanomyces root rot a top concern. If the pathogen is present in the field, growers should aim for a six- to eight-year break period.

“Although we have fewer pea acres than other provinces, it might even be a greater concern here due to wetter conditions from time to time,” says Tkachuk.

She also reminds growers that long rotations have other benefits too. They prevent volunteer plants from becoming weeds, help diversify herbicide programs and provide opportunities for soil fertility management and nutrient building.

New threat in the neighbourhood

Tkachuk warns producers to watch out for soybean cyst nematode (SCN) in their soybean crops. The openings on the roots of soybean plants infected by SCN may cause the plants to be more susceptible to the development of root rot and seedling diseases.

While the pest was identified in the province for the first time in 2019, it is currently not a big problem. However, as soybean production continues, so too will SCN’s presence, says Tkachuk. Four fields have tested positive for SCN in four out of 18 municipalities so far.

“There were only four fields and at very low levels, so consistent with recent establishment,” she adds.

Tkachuk is encouraging farmers to scout randomly for SCN symptoms. Once above-ground symptoms are evident, growers can expect up to 30 per cent yield loss. She recommends scouting high-risk areas, such as low spots and field approaches.

To determine if the pests are present, soak the roots of plants taken from random locations in your field in water and look for small, lemon-shaped cysts on those roots. Note that cysts will be smaller than root nodules.

Key management strategies for SCN include rotation and using resistant varieties. “The way it works with that pest is if you’re rotating away from its main host, which is thankfully only soybeans, you’re just starving the pest,” said Tkachuk. “The longer the break period, the less it can survive and the less it will hurt your yield.”

Tkachuk also warns growers some soybean varieties have lost resistance to SCN because of how widely they’ve been used in past years.

Scouting calendars for pulse and soybean crops in Manitoba are available at the Manitoba Pulse & Soybean Growers website.

Saskatchewan

Saskatchewan pulse crop growers had their share of disease pests in 2020. In peas and lentils, the biggest issue is root rot. Aphanomyces is the main pathogen of concern and Fusarium is a close second.

Sherrilyn Phelps, agronomy manager at Saskatchewan Pulse Growers, says there’s a lot of information on the organization’s website that explains how to reduce the risk of aphanomyces root rot for 2021. For example, field choice, rotation and testing for the pathogen are important, she says.

Anthracnose continues to be the disease of concern in lentils. It was a problem for growers in 2020, and once it starts appearing, says Phelps, it can be very aggressive.

Saskatchewan Pulse Growers has been involved in a project that’s evaluating the level of anthracnose insensitivity to strobilurin fungicides.

“There was a concern brought forward this past spring regarding high levels of resistance and we are just in the process of getting the samples from this summer analyzed through the Ag Canada station at Swift Current with Michelle Hubbard,” says Phelps. “We don’t have the results from the over 100 samples that were submitted through the survey (last) year, but managing anthracnose that has potential resistance to the Group 11 herbicides is a real concern going forward.”

Aschochyta rabiei, which causes aschochyta blight, remains the pathogen of concern in chickpeas, especially as producers begin to see insensitivity to Group 11 fungicides. Phelps says there’s information on the Saskatchewan Pulse Growers website about how to manage aschochyta as well as fungicide insensitivity.

Mystery disease

A second issue affected chickpea acres last year, but agronomists don’t know what it is yet. What agronomists are currently calling a “chickpea health issue” was found in almost every chickpea field in the province in 2020. Fields with greater incidence of infection saw some yield loss, while less-infected fields were not affected yield-wise. In some cases, the health issue delayed maturity, which led to quality issues.

“We’ve had it now for two years and we’re working to try to identify what it is,” says Phelps. “It could have a link to a disease of some sort, but we don’t know yet.”

The best advice at this point includes reducing risk by watching for residual herbicides, application timing and potential nutrient deficiencies and managing for disease.

In fababean, Saskatchewan Pulse Growers identified three foliar diseases of concern — botrytis chocolate spot, stemphylium blight and alternaria leaf spot.

“We still don’t know the disease impact on yield, but there’s some research projects underway evaluating that,” says Phelps.

In dry beans, blight has been the main concern. There were not many issues in soybeans in 2020, besides the drier conditions in August, which affected yields.

Alberta

Similar to Saskatchewan and Manitoba, aphanomyces root rot is the biggest issue in lentil crops in Alberta, although lentil acreage is very localized. In a wet year, the biggest issue in lentils is sclerotinia.

“Sclerotinia moves into the lentils right around flowering, the canopy closes and then we’re done,” says Robyne Bowness Davidson, Alberta Agriculture and Rural Development pulse research scientist.

Just like their neighbours to the east, Alberta’s pea growers are also challenged by aphanomyces. Alberta tends to have wetter, heavier soils that are higher in organic matter, so when aphanomyces moves in it can be quite devastating, says Bowness Davidson. Adopting best management practices, including planting high-quality seed into clean fields, are the only solutions for aphanomyces, she adds.

Although fababeans are susceptible to diseases, the crop faces no real issues in Alberta. Fungicides are available for any diseases that do occur.

In Alberta, chickpea acreage is much lower than it is in Saskatchewan. The good news is in this province, the mysterious health issue observed in Saskatchewan was not found in 2020.

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But the destruction didn’t stop there. Of the 4,500 acres the family farms (both rented and owned), about 2,200 were affected by the fire. Heavy winds took the ash, which would have provided nutrients, and much of the soil. In some places there were four-foot-deep drifts of soil in the trees. It even filled the ditches.

Since then, soil health has been an important focus for Kirschenman.

“We are in a starting over position on half of our acres from a soil health standpoint,” said Kirschenman during a presentation he made at 2020’s Farm Forum Event last November.

Soil health improvement ongoing

Historically speaking, Harvest Moon Farm, first purchased in the 1950s, didn’t always put soil first. Through the 1970s and into the 1980s, the farm followed a fallow system that left plowed and tilled land unplanted following harvest for one growing season. This left the land subject to soil erosion, said Kirschenman. In some places, the erosion was so bad fence posts sat just six inches above the soil. The hilly landscape left the soil prone to water erosion as well.

Improving soil health has been ongoing on the farm. In the 1990s, the Kirschenmans began chem fallowing, and continued to do so up until 2012. In the early 2000s, they further diversified crops by adding peas, flax and canola to the rotation, producing as many as eight crops per year. They tried adding corn, sunflowers, soybeans, fava beans, peas and lentils as well, but have since backed off some of those options as they’re too challenging to manage.

Kirschenman has tried integrating cattle onto his land as well. He likes that the residue and manure stay on the ground, but says it’s difficult to make it work.

“It is really hard to make it pay anywhere near what an annual crop would pay in this area without intensive management,” he said. “Even with intensive management, we’d still have to run the numbers hard.”

After the fire, Kirschenman tackled the soil health challenge head on. He combined a variety of soil health management tools on the farm. He incorporated multispecies cover crops, diversified his rotation and preserved crop residue to protect the soil from further erosion. As much as possible, he uses disc drills and stripper heads.

Cereals are also an important part of the rotation, as they’re a more natural fit in mixed grass prairie, he added. “We have to try to mimic that,” he said. “Annual cereals, and especially winter cereals, are the best way for us to build up that residue.”

However, incorporating soil armour and reducing tillage are the most important soil health principles on the farm right now.

“If we don’t do that none of the other processes work,” said Kirschenman. “We can’t grow diverse crops if we don’t keep the moisture for them. We can’t integrate cattle if the cattle eat all of our residue and we’re left with bare fields.”

NRG Farms

Building soil health for future generations is the main goal on Tim Nerbas’ farm in Waseca, Sask., as well. Nerbas also shared his strategies for improving soil health at the conference, which include constant cover, crop diversity and zero tillage.

Nerbas took the first steps toward improving soil health on NRG Farms more than 20 years ago when he made the decision to eliminate tillage entirely. Some of the farmland had not been tilled for more than 30 years, so no-till was not new to Nerbas. From there, he focused on crop variety and diversity, which he sees as crucial to soil health. In a given year, Nerbas grows wheat, barley, oats, canola, peas, fava beans and flax. Some years, he intercrops canola and peas.

Nerbas says he uses nature as his guide. “In nature, we see lots of diversity and the ground is always covered,” he said. “That’s what we’re trying to replicate.”

However, more crop diversity means more complex weed management, said Nerbas. “Sustainable ag is not something that is simple, but simple ag is not sustainable,” he said.

Often overlooked is the soil microbial community. There’s still so much to learn about these communities, but we do know they need to be fed, said Nerbas.

Ultimately, Nerbas aims to ensure economic profitability while feeding the soil to keep it healthy and minimizing erosion. He believes looking after the soil better prepares him for the variable weather conditions that seem to be the new norm.

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Through their interconnectivity, these three properties play a crucial role in soil health and affect key parameters such as aeration, soil organic matter and pH. Coming full circle, those same soil health indicators play a vital role in microbial activities, such as carbon and nutrient cycling.

Why it matters: A good soil assessment looks beyond chemical and physical attributes and also considers biological health. The diversity of soil microorganisms is great and their needs should be considered in your soil management plan.

A good soil assessment, therefore, looks beyond chemical and physical attributes to further evaluate that third component — biological health. Yamily Zavala, Soil Health Lab manager at Chinook Applied Research Association (CARA), provided an overview of soil health assessments at the last November’s Farm Forum virtual conference, with particular attention to soil microbial communities and their functions.

As manager of CARA’s Soil Health Lab, Zavala’s focus is on the evaluation of physical and biological soil properties. Regular and thorough assessments allow growers to monitor changes in soil properties as they work to better soil management decisions. There is a great diversity of soil microorganisms. Their needs should be considered when starting a new soil management plan, said Zavala.

Regardless of the lab you choose to carry out your soil assessment, make sure the most important soil health indicators are evaluated, recommends Zavala.

Soil aggregates stability

Samples are first evaluated for soil aggregate stability. This is done by placing soil in a sieve and running water through it.

“When the soil is stable, aggregates will stick together and remain in the sieve,” said Zavala.

The higher the number, the better the aggregate stability.

Soil microbial activity

Lab technicians also assess samples for bacteria, fungi, protozoa and nematodes. In fact, soil microbial respiration is one of the most important biological soil health indicators. Using a test developed by Cornell University, soil microbial activity can be measured by releasing the carbon dioxide trapped in the soil into a chamber. Larger respiration values indicate higher activity by soil microbial communities, said Zavala.

Having a strong soil microbial community will improve physical and chemical constraints. When soil is managed appropriately, active carbon is an indicator of the small portion of soil organic matter readily available as a food and energy source for soil microbial communities. Having food for the biology in the soil helps maintain a healthy soil food web, Zavala said. It’s also a good indicator of soil health responses to changes in crop and soil management.

Fungal-to-bacterial ratio

Most farmers understand the chemical aspect of their soil health assessments. However, the biological aspect is just as important, she said. The fungal-to-bacterial ratio, for instance, is an important indicator of soil health.

In the lab, soil samples are diluted into special solutions and a portion is processed to assess biophysical indicators. Bacteria are then counted and measured.

“Each creature in the soil has a function,” said Zavala.

Ciliates, for example, are indicators of physical soil health constraints and play an important role in the soil food web. Protozoa are single-celled microbes that eat bacteria, other protozoa, soluble organic matter and sometimes fungi — and when they do, they release nitrogen that can be used by the plants and other members of the soil food web.

Nematodes

Nematodes are also a good indicator of soil health, said Zavala. Where there are too many nematodes, particularly of just one species, soil health is likely poor. Too few nematodes is also an indication of poor soil health.

Nematodes play an interesting role in the soil. They feed on other soil microbes — some of which are bad for the health of the crop — including bacteria, fungi and predators.

“Nematodes, in general, are considered the bad guys,” said Zavala. “But less than 10 per cent of them do damage to your crop.”

The rest of them are “good guys,” she said, because they improve nutrient cycling.

Fungal-feeding nematodes attack fungal communities in the soil, including the ones that are not good for the crop. If fungal communities are not present, warned Zavala, they will feed on the roots of crops. When microbial communities are in balance, however, they act as a natural biological control in the soil. Applying too many chemicals to the soil kills natural predators, she added.

A soil test that includes a complete assessment of the soil’s physical, chemical and biological attributes is critical, Zavala emphasized.

“It is important to benchmark your soil to monitor changes in soil biology and correlate them with any improvements on the specific constraints you have in the soil,” she said.

Too often, soil tests evaluate micro and macronutrients present in the soil, as well as organic matter, pH, soluble salts and cation exchange capacity, but forget to assess the microbial communities present.

“Healthy soils have lots of microbial interactions,” said Zavala. “Soil without biology is dead soil.”

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Fungicides remain the most effective tool when dealing with sclerotinia, says Jurke. “On average, they reduce the amount of sclerotinia infection by about 80 per cent, and even the very best resistance on the market doesn’t provide that level of control. In high-risk situations, a fungicide application is certainly the best tool in order to manage the disease.”

A high level of disease can lead to 20 to 30 per cent yield loss, and in some cases more. However, the difficulty with applying a fungicide is it only provides economic value in high-risk situations.

“The difficulty is knowing whether or not it is a high-risk situation for the development of the disease,” says Jurke.

In Western Canada, a large number of acres are devoted to canola production each year, as well as other host crops, including pulse crops, sunflower and soybeans. Furthermore, rotations are often tighter than recommendations, giving the pathogen more opportunity to develop.

New tools

There are new tools available to help growers quantify how much pathogen is present at the time of flowering, including DNA petal tests and spore traps. 20/20 Seedlabs, for instance, developed the Spornado, a simple spore catcher that traps airborne spores on a specialized filter cassette in the field. Currently, Spornado focuses on sclerotina stem rot and Fusarium graminearum.

In reality, it’s the weather that determines if the disease will become a big problem; in particular, how much rain falls prior to flowering, and how much rain falls during flowering.

“If we could have a really good weather prediction system that would tell us how much rainfall is going to happen, then we would know even more specifically how much risk is there,” says Jurke.

Since weather prediction isn’t perfect, farmers are left to make their best guesses. It really comes down to moisture and how much moisture was in the crop in the two to three weeks leading up to the flowering period, and how wet and humid the canopy is during the flowering period, he says.

What makes managing sclerotinia stem rot even more challenging is the window to respond is fairly narrow. Most fungicides need to be applied at the 20 to 50 per cent bloom stage, and the majority target 30 per cent bloom.

“It’s only a matter of days for the crop to be in that stage,” says Jurke. “A grower needs to be scouting the fields right at bloom stage to make their estimation as to how wet it has been prior to that period, and what the forecast is going to be for the next couple of weeks.”

The other factor that’s important to consider is the actual yield potential of the crop. If the crop is not good, the cost of application is not justified. Crops with higher yield potential in the 50 to 60 bushel per acre range warrant protection.

New varieties offer tolerance

Currently, there are a couple of varieties (45CS40 and D3154S) that are considered sclerotinia stem rot tolerant. Jurke refers to them as “partially resistant” because they don’t provide complete control of the disease.

“The pathogen still infects the plants but what happens is the infection just moves slowly through these varieties compared to other ones.”

Using a tolerant variety can reduce disease impact by an estimated 60 per cent. “But that level of control is not as good as a fungicide,” he adds.

Jurke says there’s much excitement about new germplasm that’s currently under development. In Asia, new resistance genes have been identified, and are currently being backcrossed and bred into current resistant varieties. However, it will be five to seven years before those varieties come to market.

“But these look like truly resistant varieties, like they could potentially be replacing fungicide applications,” says Jurke. “When those hit the market, that will be pretty awesome.”

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Why it matters: Mistaking verticillium stripe for sclerotinia stem rot or blackleg could cost you time and money.

Since verticillium stripe is new to Canada not much is known about how to manage it. In fact, much of what is known about the disease has been gathered from experts in Europe. Not all of it is applicable in Canada.

One of the confounding features of verticillium stripe is symptoms do not appear until later in the season, post-harvest, says Canola Council of Canada (CCC) agronomist Justine Cornelsen, who is the organization’s lead on the disease. In years where harvest is delayed, farmers found infected crop in a tangled mess around their combines.

“The plants become really fragile and so they start to strip away,” explains Cornelsen. “Very similar to if you have a bad sclerotinia case. We’re in the early stages of trying to figure out this disease and what it does, and what it potentially might do to our canola production here,” she adds.

What they do know is European farmers have reported losses ranging from 10 to 50 per cent. Cornelsen notes, however, that European farmers are growing winter varieties, which means their crops are in the ground much longer. This means the disease has a longer time to do damage to the crop, she points out.

Since verticillium stripe is a new disease in Canada, researchers and extension specialists have to start with the basics, including details such as identification, spread and life cycle.

It’s important to know what you’re dealing with, says Cornelsen. “Proper scouting and identification is going to change your management practices,” she says. “If you think you’re dealing with blackleg and it’s actually verticillium, you’re really going to change how you approach this disease.”

Three things you need to know

1. It looks like sclerotinia stem rot.

At the traditional scouting time, growers will notice senescing or lighter colouring on half of the stem. It looks a lot like sclerotinia, says Cornelsen, which will be particularly distressing to those who used a fungicide application to control the disease.

Cornelsen describes the senescing part as wilted, shrivelled and shrunken in. “At that point the plant is still going to be fairly hard because the other half is still green, so you’re not getting that shredding like you would with sclerotinia,” she says. “A sclerotinia plant can have white mould on it, and if the mould is dried up on it, it’s already shredding and it’s all the way around. It’s not just half of the plant.”

The key difference between verticillium and sclerotinia can be found in the stem. “When you crack open that stem, you are going to find a sclerotia body if it’s sclerotinia,” she says.

2. Microsclerotia will be present in infected stubble.

If you’re not sure what you’re dealing with at first sight, be sure to return to the field two to three weeks later, if possible. That’s when you’ll really start to see the plant shred, says Cornelsen. “Beneath it is where you see the real, true sign of the disease, which is the microsclerotia,” she says.

“The microsclerotia are extremely tiny grey flecks. The entire stem will be loaded with microsclerotia everywhere.”

Growers may confuse verticillium stripe with alternaria black spot and blackleg at this point. “As soon as you see anything black or grey, your mind automatically starts to go that way,” she says. “But that’s our true sign — the microsclerotia in the stem below the epidermis.”

3. Verticillium stripe is a soil-borne disease.

Because verticillium stripe is a soil-borne disease, the disease comes up through the root. Management tips will be similar to those used to manage clubroot, which includes rotation and equipment sanitation.

It should be noted, says Cornelsen, there is the potential for host resistance as well. Although they don’t know which varieties are more resistant than others to date, researchers are testing germplasm and they are finding differences.

“I’ve also noticed differences in variety trials in fields with verticillium. There are clear differences between varieties,” says Cornelsen.

“That’s very promising,” she adds. “We know then that we have something in the background that’s showing some levels of tolerance to this disease.”

In conclusion, Cornelsen notes, the disease can coexist with other species, so expect to see plants showing signs of blackleg and sclerotinia at the same time.

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Come spring, resting spores not only germinate where they overwintered, but they are also capable of swimming short distances in search of root hairs to infect. Once it’s present, there are no control measures that remove the pathogen from the field. It is possible, however, to curb spread and reduce incidence and severity.

Why it matters: While there are no economical control measures for clubroot once it’s in a field, it is possible to prevent further spread and to reduce its severity.

While there are no economical control measures for clubroot once it’s in the field, it is possible to prevent further spread and to reduce its severity.

One cannot know what’s in the field without scouting, so the first step to preventing clubroot is to scout. Many farmers misunderstand the timing around scouting, says Canola Council of Canada (CCC) clubroot specialist Dan Orchard. They wait until they see a dead patch and then investigate. However, farmers should be scouting well before they see anything strange in the field, he says.

Detecting clubroot

Select hotspots at random, says Orchard, pointing to entrance areas, lowlands, high-traffic spots and water runs where runoff occurs.

The best time to start scouting is in July, although it can be difficult to access fields. Right after swathing is much easier and still effective, says Orchard.

“Pull up as many plants as you can,” he says. “Look at the roots carefully, and shake off the dirt.”

While highly infected plants will have galls that are impossible to miss, some galls will be the size of a pea seed. When spore levels are low in the soil, galls will often be found on the lateral roots.

Growers who wait too late to scout may find root systems that appear like mushy sawdust, says Orchard. This is because the roots have already begun decomposing, making detection all the more difficult.

“Really late into the fall they are much harder to recognize,” says Orchard. “By the spring, most of the roots will already have decomposed.”

It’s not always easy to tell if you have clubroot. In fact, some of the best experts out there sometimes get confused. Herbicide drift and injury and hybridization nodules can look like clubroot too, warns Orchard.

One way to be certain is to send in soil and/or plant samples. Plant samples are more accurate, says Orchard, as clubroot is extremely variable within a field and even within a patch, so it can be missed with a soil sample.

Once you do know where you have clubroot, Orchard suggests keeping a record to avoid further spread. This suggestion came from Alberta farmer Curtis Henkelmann, says Orchard. Situated in the heart of Alberta’s clubroot hotspot, Henkelmann has been able to keep his fields relatively clubroot-free. He has done so by following a stringent plan and through strict record-keeping.

“If you try to just remember everything, you can’t,” says Orchard.

Risk mitigation

Minimizing risk starts with good hygiene. This means reducing soil movement and implementing a sanitation plan. Of utmost importance is incoming equipment from unknown areas needs to be extremely clean. This includes custom work and used or rented equipment. Oilfield exploration can be another source of contamination. Farmers can assess what level of risk they want to assume.

Clubroot risk mitigation also means having a sanitation plan. This involves making sure everyone who comes onto your farm is free from soil. Orchard suggests having a grassed area where large lumps of soil can be easily and safely knocked off. In fact, this is the first step to good sanitation, he says. The second step involves stopping at the edge of the field to minimize the movement of soil. Equipment should also be cleaned off between fields.

Another means for mitigating risk is to control host weeds and volunteers where and when possible. Host weeds include stinkweed, shepherd’s purse, wild mustard and flixweed.

“Make sure you don’t have these host weeds growing in your other crops or it’s like you didn’t take a break from canola,” says Orchard.

Choosing the right varieties before you have clubroot is also a crucial mitigation strategy, as is rotating resistance genetics.

“Because we’re really not good at identifying clubroot early, by default, the industry has agreed that using clubroot-resistant varieties before it gets established is a really key factor to keeping spore loads at manageable low levels,” says Orchard. “It’s that one susceptible crop too many that causes big explosions in spore loads that become really difficult to manage. And then that big spore load puts pressure on our resistant varieties and they won’t be as durable.”

You found clubroot? Here’s what to do next

If you do have infested areas in the field, CCC recommends using patch management techniques. This includes everything from telling farm workers not to drag equipment through areas to fencing off bad patches.

Grassing bad patches also helps, as it holds soil in place. Research shows some grasses have the ability to coax spores out of dormancy quicker, which helps reduce spore loads in soil rapidly. Researchers are continuing to investigate these findings.

“Time spent managing and making plans is better than time spent figuring out who brought clubroot to the farm,” says Orchard. “It doesn’t really matter how bad clubroot is around you, and it’s doubtful it would affect you enough to cause you hardship if you do these management things.”

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The 2018 canola disease surveys for Saskatchewan and Manitoba reported root rots in six per cent of fields, says Clint Jurke, Canola Council of Canada (CCC) agronomy director. Manitoba estimated the percentage of infected plants to be around 0.3 per cent and Saskatchewan did not estimate the percentage of infected plants. Alberta has not surveyed for root rots in the last seven years.

One of the difficulties of root rot is it’s not really understood how prevalent it is, or how much damage it causes overall. “Where we do know that root rot is causing a bigger problem is often as a secondary pathogen, particularly if you have blackleg,” says Jurke. “Root rot seems to be worse in blackleg-infected plants, especially if the plants are really heavily infected.

The pathogens that cause root rot can severely affect yields, especially if infection occurs early in the season.

“Likely what happens is the plant’s defence systems are compromised by the blackleg fungus, so now the root rot pathogen has the ability to cause a lot more damage,” he adds. “It exacerbates the whole blackleg issue. It’s one of those diseases that makes sick plants even worse.”

Agronomists also note that interactions with insects, such as cabbage flies, can further exacerbate root rot. Cabbage flies produce root maggots, and when those maggots tunnel around canola roots, they open wounds where infection can set in.

Varied symptoms

Root rot complex is caused by soil-borne fungi that affect the roots of mature canola plants. The primary pathogens involved in root rot complex include Fusarium species, Rhizoctonia solani, and Pythium species. The root rot complex itself includes foot rot, late rot, root rot and brown girdling root rot. Of the four, brown girdling root rot is the most serious. In many cases, root rot diseases are initiated by infection early in the plant’s life.

Root rot is a serious issue in Western Canada. Losses are highest when wet soil conditions occur around early flowering and followed by dry weather later in the season. In some fields, infection levels reach as high as 80–100 per cent, causing as much as 50 per cent yield loss.

Identifying root rot can be tricky since the disease complex manifests in several different ways. Seedling diseases exhibit symptoms during the germination and emergence phase of the plant’s life. Adult root rots exhibit their symptoms at the two-leaf stage and later, and are mostly evident near the end of the plant’s life.

“The infection process may have started during the seedling stage for both types of diseases, but when the symptoms manifest determines which type of disease it will be,” says Jurke.

Early symptoms of brown girdling root rot, for instance, manifest as light-brown lesions on the taproot or main lateral roots. The roots will expand and merge, and the taproot will look as if it’s wearing a belt that’s fastened too tightly. In some cases, only a short stub of the taproot remains. In the field, plants affected by brown girdling root rot will ripen prematurely, often before any seed has been set.

Brown girdling root rot is most prevalent in the Peace River region of Alberta. Jurke says this is likely due to the region’s environmental conditions, cold soils and the frequency at which canola is grown.

Foot rot symptoms include hard, brown lesions at the base of the stem. Salmon-coloured masses will often be present in the lesions. Since the lesions develop late in the season, yield loss as a result of foot rot tends to be minor. When lesions occur earlier in the growing season, they can cause premature ripening and reduced yield.

Root rot symptoms are more variable in both colour and shape. According to CCC resource material, symptoms can be grouped into four types: a light-grey, oval lesion on the upper taproot; a dark-grey discolouration of the lower taproot and internal tissue (this will later turn black); a light-brown, soft, widely spread taproot lesion; or a dark-brown, sunken, sharply defined taproot lesion.

In canola-growing regions symptoms will occur sporadically. Generally speaking, Brassica rapa varieties tend to be more susceptible to root rot. Brown girdling root rot is not commonly seen outside of the Peace River region. A test should be conducted in order to confirm the disease’s presence.

Root rot prevention

Preventing root rot starts with crop rotation, as the risk of root disease tends to increase when rotations are shorter. Jurke says growers should consider including peas or other pulse crops in the rotation to reduce disease severity. Not only will they help lengthen the rotation, but they’ll also improve nitrogen levels in the soil.

“Pulse crops are infected by different pathogens, and so the opportunities for those canola-infecting pathogen strains to increase is diminished,” says Jurke.

Likewise, it’s also important to maintain recommended fertility levels in the soil, particularly nitrogen, phosphorus, potassium and sulphur. Nitrogen, in particular, decreases disease severity.

“When plants are stressed, then their ability to fight off root infections is diminished,” says Jurke.

Disease management starts at planting — even before farmers get out in the field. To keep disease at bay, choose certified seed, which will have a fungicide package, says Jurke.

“Risk goes up dramatically if the seed is not treated,” he says.

Note that no economical chemical controls are available for brown girdling root rot or any of the adult-plant root rot diseases.

At planting, good stand establishment — so a vigorous, uniform crop — is crucial for preventing disease. Pay attention to soil temperature, planting depth and uniformity, and make sure seeds are planted into a firmly packed seedbed, says Jurke.

“The longer seeds are sitting in an ungerminated or slow-growing state below the soil’s surface, the greater the risk,” says Jurke.

Other management tips include practicing good weed control. Any weeds that are in the Brassica family are potential hosts, says Jurke. Problematic weeds include shepherd’s purse, stinkweed, volunteer canola and flixweed.

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Currently, blackleg is present across the Prairies but at low levels. The disease rears its head a number of times throughout the season, but the best time to scout is right before swath timing when growers see 60 per cent seed colour change, says Cornelsen.

“That way, it’s still easy enough to identify the differences between the different plant diseases,” she says. “If you go later in the season, plants start to really decompose so you can’t really tell what’s causing the issue or what the symptoms are.”

To scout, go into the field, pull plants up and cut the plant through the root material right at the base of the stem and look for internal blackening. “Of course, not everything within that cross-section is necessarily blackleg, but it’s usually the predominant disease that we’re dealing with, and if you pull up enough plants you start to tell the difference between other diseases,” she says.

To mitigate yield loss, growers first need to know what they’re dealing with. “I think that’s where blackleg goes undiagnosed,” says Cornelsen. “Producers aren’t necessarily looking for it. Because of the introduction of resistant varieties, blackleg was kind of put on the back burner.”

With a good rotation — canola once every three years — farmers should be fine in terms of blackleg. Infected residue will break up and disintegrate under an extended rotation, says Cornelsen.

“The longer you’re out of canola and managing volunteers will help you to really lessen that inoculum in the field,” she added. “Scouting, crop rotation and the use of resistant varieties — those are our top three. If you’re using those three, then you should have no issues.”

Where growers are seeing issues is where rotations have tightened, building up the perfect storm for pathogens. In areas that restrict crop options, Cornelsen suggests that growers rotate genetics effectively.

At one time, many varieties had no resistance at all. “If you’ve never walked into a disease nursery or seen Westar — a susceptible variety — growing, it’s unbelievable seeing what this pathogen can do,” says Cornelsen.

Today, all canola varieties available in Canada are resistant to blackleg, but some genetics will better match a particular race of blackleg than others. For best results, test stubble to identify the race or strain you’re dealing with and choose the best variety accordingly.

When to apply fungicide

Growers who want to apply fungicides will want to scout for blackleg first thing in the spring. Look for old residue that is housing spores and leaf lesions on cotyledon canola. Assess if conditions for spore production have been ideal.

Fungicide use is effective when applied at the correct timing and on susceptible varieties. “When you know your resistant variety isn’t working as effectively as it should that’s where an early-season fungicide application would be warranted,” says Cornelsen. “Of course, the earlier the better. You’ve got to coat plants before the pathogen is producing spores.

“And that’s why it’s not widely used here in Canada,” she adds. “Because you’re pretty much spraying dirt when you’re spraying cotyledon canola.”

The recommendation for foliar fungicides is to spray at the two- to six-leaf stages. In the near future, expect fungicide seed treatments for blackleg, which will give canola seedlings protection during that stage where there’s the greatest risk for yield loss.

Clearing up confusion

There are a couple of confusing points around blackleg and canola disease in general, says Cornelsen. For example, blackleg is a stubble, residue-borne disease, whereas clubroot is soil-borne.

In Manitoba, in particular, growers are struggling to tell the difference between blackleg and verticillium stripe. The first case of verticillium stripe was found in Canada in 2014. Its impact on canola has yet to be determined.

“We’re thinking with some of our disease surveying here in Manitoba, we’ve probably been calling things blackleg when it’s actually verticillium stripe,” says Cornelsen.

Prior to swathing, blackleg will be prominent in stem cross-sections with black spots, whereas verticillium will be very subtle at that time, explains Cornelsen. Potentially, verticillium stripe will have a grey-brownish hue, starburst pattern or grey specks. Blackleg will produce pycnidia spores on the outside of the stem, she says. Verticillium stripe will have microsclerotia below the outer stem wall, but the outer layer must be peeled back to view them.

Symptoms for verticillium stripe are better seen later in the season, post-harvest.

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While there are several diseases that impact oat, over the past 20 years crown rust has been the major one, says Randy Kutcher, a professor at the University of Saskatchewan. And while breeders put a lot of effort into developing new varieties with better resistance, the crown rust pathogen evolves and breaks down that resistance fairly rapidly.

Rust fungi are obligate biotrophs with a complex life cycle, explains Kutcher. Their existence is dependent on living hosts, both oat, which is the primary host, and an alternate host. While they cause a lot of damage in oats, their sexual lifecycle takes place on the alternate host, a woody shrub called buckthorn, which tends to grow along rivers. Where the alternate host is present, growers will likely see crown rust more often and earlier in their oats. The disease usually ramps up around the end of July.

Crown rust fungi can also overwinter on oat residue. Come spring, the spores are released and infect the buckthorn. Then, the spores produced on the buckthorn are released and, once again, find nearby oat crops. If there is no alternate host, the inoculum will travel up from the United States. But where the alternate host is present, the spores will be released much earlier.

“If you don’t have the host, you have a lot better chance of containing the disease and reducing the variability, so you don’t get new races of the pathogen,” says Kutcher.

Crown rust-resistant and high-yielding varieties

Managing disease in oats begins with choosing the right variety. And while many growers still opt to plant AC Morgan — it’s an older, high-yielding variety — it’s also very susceptible to crown rust.

“We’ve had very good resistance in many of the varieties but in the old ones, the resistance is not effective anymore,” says Kutcher.

Many growers are happy to accept the risk in favour of yield advantage, but Kutcher says it’s not necessary. There are “very good varieties” coming out of the Crop Development Centre breeding program led by Aaron Beattie, he says. These varieties have good resistance to crown rust and they’re high yielding, Kutcher adds.

“Breeders have to keep up with new genes for resistance against crown rust,” he says. “They’ve been successful; there are very good varieties that you don’t have to spray.”

When to apply fungicide

Crown rust can dramatically impact yield in oats, sometimes taking as much as 50 per cent and up to 75 per cent of the crop yield in worst-case scenarios. It all depends on how early it strikes and whether or not the variety has resistance.

Epidemics tend to be worse when conditions are warm and wet. The disease damages the leaves, effectively reducing photosynthetic area. When the pustules erupt through the leaf surface, the plant also loses a lot of water.

“If you’re going to spray for it, you need to be out there in early July,” Kutcher advises. “Well before the panicle emerges, so by flag leaf for sure. Before the flag leaf would be better.”

Crown rust is also an issue in Manitoba, although the last major outbreak was in 2005. At that time, agronomists noted that some of the resistance varieties had was no longer effective. This indicates the pathogen has changed, says Manitoba Agriculture cereals specialist Anne Kirk.

Manitoba has been dry for the past few years, thus outbreaks have been minimal. Agronomists haven’t surveyed for the disease either, so while it is a disease that farmers deal with every year, it’s difficult to know if or where big outbreaks have occurred, says Kirk.

Millers usually offer recommendations for varieties, and those recommended varieties usually include a disease package, she says.

Other oat diseases include stem rust, leaf spot, barley yellow dwarf, smut and fusarium.

There are some leaf spot diseases that can be found in oats, but their impact is generally quite low, says Kutcher. “Usually, we don’t think they cause much yield loss, at least in Saskatchewan,” he says.

Stem rust is also possible, but breeders have it under control, he adds.

Barley yellow dwarf can be a problem in oats, although agronomists don’t really know how much yield loss it causes. While scouting is recommended, it is hard to predict and there is no treatment for the disease. Barley yellow dwarf will usually appear around late July.

“There’s not a whole lot you can do about barley yellow dwarf,” says Kutcher. “It seems to depend on the season whether the aphids spread it into the crop or not. It’s quite distinct in oats. You see quite yellow to red leaves that are highly infected on some occasions.”

Smuts are also possible, although Kutcher says he doesn’t see a lot in surveys. This is likely because of the use of resistant varieties and seed treatments.

Finally, there has been some concern about fusarium in oats. The nature of the panicle reduces concern. “You might see individual kernels or flowers that are infected, but it’s not as much of an issue as it has been in wheat,” says Kutcher.

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