Fighting Fusarium Head Blight

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Fusarium head blight damage in wheat. (Photo: Kelly Turkington)

Cereal growers in Alberta have a new weapon in the fight against fusarium head blight (FHB). It’s an online risk assessment tool that helps farmers and agronomists decide whether to apply fungicides based on the likelihood of the disease turning up in their area.

Brian Kennedy, grower relations and extension manager for the Alberta Wheat Commission (AWC), says the tool was launched in the summer of 2017 following requests from wheat producers in the province.

“They had been seeing fusarium risk maps from Manitoba and Saskatchewan … and they asked us to develop something,” he says.

The tool was developed for the AWC by numerous partners, including Ralph Wright and Pavel Pytlak from Alberta Climate Information Services, plant pathologist Michael Harding and crop specialist Neil Whatley from Alberta Agriculture and Forestry, and Agriculture and Agri-Food Canada plant disease researcher Kelly Turkington.

“We’ve been lucky [in that] we’ve had a couple of years with lower fusarium head blight, but because this is a weather-related disease, growers need to be aware of it and manage their risk by following best management practices every year,” says Turkington.

“This was really to get something out and available to producers, so they can start looking at gauging the potential risk of fusarium head blight based on weather conditions.”

Turkington says while FHB is a relatively new disease in some areas of the province, the disease risk is more widespread in Alberta than it was a decade ago.

“The pathogen has become more frequently found not only in southern Alberta, where it causes production issues and downgrading and so on, but also outside of that region,” he says.

“We’re at a point now that in a number of areas in Alberta, producers are not so much concerned about introducing the pathogen as they are about effectively managing it so that the impact on yield and especially grade and also mycotoxin contamination is mitigated as best possible.”

Weather Station Data

The FHB risk assessment tool works by pulling data from weather stations across Alberta to provide a localized risk warning gauge. This data consists of nearly 130,000 hourly weather observations that Alberta Climate Information Services collects every day from over 370 stations provincewide.

“We think it’s a great use of the data that the weather stations are collecting,” says Kennedy.

The disease severity is calculated on a Manitoba FHB risk assessment model that’s based on air temperature, relative humidity and rainfall over the previous seven days. The Alberta tool is active between June 1 and August 15 each summer, the time when a wheat crop is most susceptible to FHB infection and corresponding losses, both in terms of yield and quality.

The tool, which is designed to be viewed on mobile devices, can be found at agriculture.alberta.ca/acis/fusarium-risk-tool.jsp. The website also includes best management practices for controlling fusarium head blight.

To access the FHB risk gauge, users click on a red pin in the top left corner which opens up a map of Alberta with all of the weather stations marked with a green dot. They can then zoom in and click on the green dot closest to their field, which then brings up the risk gauge for that location.

“A farmer can look at the weather station closest to their field and keep an eye on that, and when they see that it is high risk and their crop is in the floret stage when it’s liable to be infected, then they can make a decision on whether or not to apply a fungicide,” says Kennedy.

Turkington says for some producers, “having this additional piece of information provides some peace of mind.”

Kennedy points out that wheat farmers who apply fungicides regularly to guard against FHB infection can save money with the tool by not having to spray as often. By only spraying when the FHB risk is highest, he says, “this also mitigates the risk of resistance building up in the fungus.”

Kennedy says he has heard good things about the FHB risk assessment system from growers across the province. “They see it as a useful tool.”

Kennedy cautions that weather isn’t the only consideration when assessing FHB risk. Farmers need to be aware of other risk factors such as:

  • The stage of the crop
  • The level of fusarium infestation in their area
  • The susceptibility of the variety seeded
  • If the seed was infected with fusarium
  • If a seed treatment was used
  • The history of the crop rotation in the field
  • Past stubble and straw management practices

New Features

Kennedy says the system’s developers chose a mobile friendly website rather than an app as a platform for the tool to make it easier to use.

“The advantage for users is they don’t have to install something on their mobile device. We tend to get a lot of apps on our devices that are always updating or sending us reminders, which leads to a lot of them being deleted. So, if this is added to their favourites on their browser on their phone, they can look at it at any time without having to install any software,” he says.

Kennedy notes that a number of new features were added to the tool this past growing season, including pest management recommendations and risk assessment maps for alfalfa weevil, bertha armyworm and wheat midge.

Data related to growing degree days and corn heat units was also added in 2018, and there are discussions about adding more features in 2019, Kennedy says.

According to Turkington, the hope is to update the model for weather predictions in the risk calculations for fusarium head blight.

“The models are continually being refined,” he says. “If you look at some of the recent risk maps in the United States, they’re starting to focus now on mean relative humidity over the previous 14-day period, but it was felt we could start with the model version currently being used in Manitoba, at least in the initial phases of the project and then update as needed.”

Kennedy says more work needs to be done across the entire Prairie region to ground-proof the disease risk assessment models for Western Canada, and that it’ll take a couple of years of scientific study to incorporate weather forecasts into the Alberta FHB tool.

Southern Alberta Clubroot Response Workshop

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Clubroot was confirmed in 4 fields southeast of Calgary in the fall of 2018.

This meeting will help you gain a better understanding of the clubroot pathogen in the context of southern Alberta and teach you how to limit the impact of clubroot on your community.

There will be plenty of time for discussion, and representatives from southern Alberta municipalities and seed companies will be available for questions throughout the day.

SPEAKERS & TOPICS

Local Clubroot Situation Update
Autumn Barnes – Agronomy Specialist, Canola Council of Canada

Clubroot Biology, & Scouting Protocols
Michael Harding – Research Scientist, Plant Pathology Alberta Agriculture & Forestry

Finding Clubroot for the First Time: how growers can cope, action plans, realistic sanitation options and hindsight
Dan Orchard, – Agronomy Specialist, Canola Council of Canada
John Guelly – Canola Grower and Alberta Canola Director

Understanding Clubroot Pathotypes and When to Deploy Resistant Varieties
Stephen Strelkov – Professor and Clubroot Research Scientist,  University of Alberta

Perspectives from Municipalities
Jeff Fleisher –  Rocky View County
Aaron Van Beers – Leduc County

For more information, click here.

Source: Alberta Canola

 

Pea Leaf Weevil Risk Map from 2018 Survey Season

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The annual pea leaf weevil (PLW) survey that is conducted by the Alberta Insect Pest Monitoring Network was released in early December. This important tool can provide insight into PLW pressure in your region of the province. The Alberta Insect Pest Monitoring Network is a collaboration between Alberta Agriculture & Forestry staff, independent agronomists and pulse growers across the province who cooperate in providing access for monitoring and survey of adult feeding. While the maps represent observed notching in the leaves of pea and faba bean plants by the adults, the damage is done by below ground feeding on nodules by the larvae. The publication of these maps is not a forecast for the 2019 growing season, but rather a summary of where adult feeding was located.

The only tool growers currently have to suppress the damage (as control is defined as >80% reduction) is through seed treatment with a registered neonicotinoid. Thiamethoxam (CruiserTM) and Imidacloprid (Stress ShieldTM) are the actives that can provide a window of protection so that pulse seedlings and their newly-formed nodules can symbiotically fix atmospheric nitrogen into a usable form for the plant.

Scott Meers, who leads the Alberta Insect Pest Monitoring Network, advises growers treat pea and faba bean seed when in regions with PLW pressure and along boundaries of where adult populations are present.

“Seed treatment is the only effective tool to limit the damage from this pest,” Meers said. “A foliar insecticide is not recommended as it is simply a revenge killing. The adult populations overwinter in alfalfa, roadside perennial legumes and pulse stubble. They move into new pea and faba bean crops in the spring. Goliath spraying does little to limit overall population or protect against yield loss.”

Research is underway to better understand the impact of PLW on the yield of peas and faba beans. There is also the ongoing hunt to find natural predators of this pest. Information on predators and parasitoids of many of the insect pests across Alberta and the prairies are available through the Field Heroes initiative. In preparation for the 2019 growing season, Alberta pulse growers should familiarize themselves with the PLW life cycle, and the current PLW pressure in their region. It is also recommended that growers inform themselves as to the natural predators and parasitoids that are present in their fields, keeping problem insect pest populations in check.

Full PLW map and other information PLW life cycle information available here: http://www1.agric.gov.ab.ca/$Department/deptdocs.nsf/all/prm16763
Field Heroes initiative and information is available here: http://www.fieldheroes.ca/

Source: Alberta Pulse Growers

Clubbing Clubroot: An Update On Breeding Clubroot-Resistant Canola

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While Bayer CropScience undertakes much canola breeding research, such as in the greenhouse pictured, clubroot resistance research is conducted in a highly-secure lab to prevent the spread of the pathogen. (Photo: Bayer CropScience)

On the Prairies, clubroot appeared in Alberta in 2003, in Saskatchewan in 2008 and Manitoba in 2013. As any grower can tell you, it’s a nasty canola disease that usually worsens in a field every year, partly because the spores are very easy to spread and so hardy they can survive for up to two decades in the soil. Combine this fact with the strong prices that canola fetches these days – widely encouraging back-to-back or two-year rotations – and you have a big problem.

Companies are certainly moving as quickly as possible to produce seed with effective resistance to clubroot, but breeding to defend against this particular pathogen involves navigating a wide range of complex challenges.

“Clubroot has a very short lifecycle resulting in several generations per season,” explains Dr. Marcus Weidler, vice president of seed operationsat Bayer CropScience, “enabling the pathogen to react to changes in its environment very quickly, including new crop resistance genes.”

Dr. Jed Christianson,pathology lead at Monsanto Canada, explains that clubroot’s large and quickly-adapting population sizes means that it takes relatively long canola rotations of three or four years to see significant drops in the number of viable spores in the soil, and very long rotations of over 10 years for spores to effectively disappear.

“Each gall produced on a canola root can contain billions of spores,” he says. “So, given the numbers of spores generated, even very rare events like the emergence of individual spores that have gained the ability to infect resistant canola will happen over a fairly short number of cropping cycles. A one in a billion event doesn’t seem that unlikely to happen when you’re given 20 billion chances.”

Combine this with the fact not all clubroot pathotypes (races) have been identified, and it’s therefore difficult, explains Weidler, to develop a canola variety that is resistant to all potential pathotypes to which a plant may be exposed.

Dr. Igor Falak reminds us that it was in2013 that a new clubroot pathotype was identified, one to which all canola varieties on the market carrying resistance to the original 2003 pathotype were susceptible. Although hybrids with the initial type of resistance continue to hold their own on most infested acres, the number of fields with the new pathotype is increasing annually. Falak, senior research scientist with Corteva Agriscience, blames this situation on “years of canola-on-canola.”

In addition, he notes that although clubroot “is similar to another disease of canola (blackleg), where canola products may carry race specific resistance,” clubroot-resistant canola varieties “do not have ‘fallback’ resistance mechanisms, unlike blackleg-resistant products that also have a different type of stable resistance.”

More breeding challenges are found in the fact that because canola plants carry no clubroot resistance genes, all the major seed companies are actively testing resistance genes found in rutabaga, cabbage and turnip. However, Weidler notes that because these species are only remotely related to canola, it’s far from easy to transfer genes between them without also transferring additional unwanted genetic “baggage” that negatively impacts yield, canola quality or agronomics.

If all this wasn’t enough, clubroot is a challenging organism to deal with, having unique characteristics – described by Weidler as a form of life “somewhere between a bacterium and a fungus.”

Christianson concludes that the biggest challenge in creating clubroot-resistant canola seed is to introduce resistance “while continuing to improve hybrid performance for yield, maturity, standability, resistance to other diseases, harvestability, seed quality and all of the other attributes that are important to growers’ success.”

Breeding Steps to Develop Clubroot-Resistant Canola Seed

Christianson says the steps involved in breeding clubroot-resistant varieties are relatively simple, and that any breakthroughs relating to resistance genes “are really just the discovery and characterization of more of them through concerted screening efforts.”

The entire process is a matter of crossbreeding canola with resistant relatives through normal pollination procedures and recovering offspring that are clubroot-resistant. “Those offspring then have to be crossed with canola again and again through many generations, selecting the resistant offspring at each generation for use in the next cycle to obtain plants that maintain resistance, but have recovered the characteristics of high-performing canola,” Christianson explains.

Weidler adds that unwanted genetic material from the resistance donor that negatively impacts the agronomic performance of the offspring is removed through several crossings of the offspring with elite parent stock. “Using molecular breeding tools, we can check the progress towards the end goal,” he notes. “Ideally, only the genetic sequence conferring clubroot resistance has been transferred and no other parts of the donor genome remain in the offspring.”

Breeding Progress

DowDupontwasthe first company in Canada to market clubroot resistant hybrids in 2009 (45H29).

“Our hybrids have multi-source and multi-race resistance to clubroot, and have a high level of resistance to the most prevalent clubroot race – race 3 – along with resistance to races 2, 5, 6 and 8,” Falak notes. Pioneer has new canola hybrids that contains a new source of clubroot resistance that confers resistance to both the initial type and new pathotypes, and can be rotated with the original resistant hybrids.”

For its part, Bayer CropScience has “identified several new potential resistance sources,” says Weidler, “and we have been able to demonstrate that these are different from what is currently on the market.”

Christianson says that as Monsanto nears “actual commercial entry into the marketplace, we will have more to share about how second-generation resistance fits in with existing resistance traits to provide a sound disease management strategy.”

No matter what resistant canola varieties are marketed, no company can predict how long a new variety will last before it’s compromised. This depends on too many factors, explains Weidler, including the resistance gene, environmental conditions and management practices.

All the companies strongly agree that the existence of varieties with resistance is only part of the clubroot solution.

Weidler emphasizes the importance of an integrated disease management approach for clubroot, and fully supports the recommendations of the Canola Council of Canada.

Falak and Christianson echo the sentiment. “All resistance traits will be effective for longer periods of time if they are used judiciously,” says Christianson. “Choosing resistant seed is only one part of a successful disease management strategy. Growers need to include crop rotation, field scouting and early detection of clubroot, and minimizing soil movement between fields on equipment.”

Falak agrees. He says following a proper canola rotation as well as rotation of resistance genes, combined with preventing soil movement and other agronomic measures “would enable sustainable clubroot management that would prolong efficacy of any new resistance sources that are introduced.”

 

How to Test Soils for the Clubroot Pathogen

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Soil tests for clubroot can have two objectives:

1. Is the clubroot pathogen present? (Yes/No test) This could be done with just one composite sample per field. Take samples (scoops) from higher-risk areas, such as field entrances, low spots or a water run that may bring resting spores into the field. For more refined results, send individual samples from each ‘hot spot’ to better understand the distribution of the pathogen within a field.

Farmers can use a ‘yes’ result to confirm that they should grow clubroot-resistant (CR) varieties. The general recommendation is to use CR varieties as soon as clubroot is found in the area (which are now most areas of the Prairies). A ‘yes’ result should also encourage heightened biosecurity and sanitation measures to keep clubroot from spreading within that field and to other fields.

Experience has shown that a positive result may not immediately lead to noticeable levels of clubroot. Resting spore levels could be too low for infection to be visible. Environmental conditions may not be conducive. Spores may not be viable. But soil tests can complement plant scouting practices for early detection of clubroot.

As a winter project, farmers could save the buckets of sampled soil and use it to grow canola plants to see if they produce galls. Remember, clubroot prefers moist and warm soil so keep the soil wet, but not saturated, and in a warm environment.

2. What is the resting spore count per gram of soil? (Quantitative test) In addition to the yes/no test, labs can also measure the amount of resting spores per gram of soil. Sample to a 15cm depth as spores in the top layer are most likely to cause yield-limiting infection. Quantitative results could be used to assess the clubroot risk level, but the ‘grey-area’ nature of this test creates problems for interpretation. Fewer spores mean lower risk, but clubroot infection can still occur at 1,000 spores per gram of soil, or less. If one field has 10,000 spores per gram and the neighbouring field has 100,000, both fields have a problem. And if a test shows 1,000,000 spores per gram, the field is clearly at risk and symptoms are likely to appear under most conditions.

Adding to the grey area is that results can be different depending on the lab (results cannot be compared lab to lab because of their different sampling, storage, extraction and analysis protocols) and the soil sampling location.

When sampling to determine the spore load in a heavily-infested area, collect samples from only that area as a composite sample from other areas may dilute the spore concentration. However, to get a fair estimate of spore load within a heavily-infested area, include soil from the canola row and from between the rows.

Eventually other objectives may be added – How many spores are actually viable and alive? What pathotypes are present and at what numbers? – which could be used to choose a variety with resistance to the predominant pathotypes in a field. This test for differing pathotypes, similar to the blackleg system, is not ready but significant progress has been made.

Source: Canola Watch

Clubroot Identified in Rocky View County Southeast of Calgary

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Clubroot has been identified in canola southeast of Calgary. Although clubroot has been found in various counties in Alberta since 2003, this is the first year the disease has been confirmed in Rocky View County.

This fall, southern Alberta canola growers should be especially diligent in scouting their canola fields for clubroot and should consider deploying resistant varieties in future canola production cycles.

Identifying clubroot as early as possible and keeping the pathogen’s spores from spreading are important steps in long-term clubroot management. With early detection, growers can take steps to contain and minimize spore loads and protect their fields. ANY method of soil movement can move the clubroot pathogen’s spores, such as tillage, dirt/dust on equipment and straw, wind or water erosion, and even animals.

Under high disease pressure, above-ground symptoms of clubroot can include stunted growth, wilting and premature ripening. These symptoms should not be mistaken for drought stress, which was common throughout southern Alberta this year. Start looking for the disease around field entrances and in areas with higher moisture or where soil movement may have occurred in a field’s history. Proper diagnosis should always include digging up plants to check for gall formation on roots. This time of year, many galls will likely have matured and decomposed into a peat-moss-like (or sawdust-like) substance around roots. If growers or agronomists find galls or a substance that looks like it might have been galls, samples can be sent to a lab for proper diagnosis. Find the labs list at clubroot.ca.

Source: Canola Watch

Clubroot Management: Harvest Theme

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Severe clubroot pulled from infested soil (note wilting of plants in the background). (Photo courtesy S.E. Strelkov, U of A)

Look. During harvest scouting, carefully examine the roots of unhealthy looking plants and also random plants chosen from around the field. Start in high risk areas, such as field approaches, then fan out in a “W” pattern. By this time of year, galls may start to break-down. Decaying galls will have a sawdust-like look and texture. If in doubt, send plant samples to a lab for identification. How to scout.

By this stage of the season, clubroot galls are starting to breakdown, leaving behind a sawdust-like material.

Test. Soil tests to determine if a field has clubroot could be done with just one or two composite samples taken from high-risk areas – like the field entrance or a water run that may bring spores into the field. Labs that do clubroot testing.

Clean. Moving soil means moving clubroot. Because more soil clings to machinery in wet conditions, wet harvests will increase the risk of clubroot movement on harvest machinery and trucks. How clubroot spreads.

Fields known to have clubroot could be done last to avoid spreading soil to other fields that do not have clubroot. Doing clubroot-infested fields last also means you’ll have more time to give equipment a thorough cleaning before bringing it home. If not doing those fields last, try to knock off as much mud and dust as possible before leaving the field and going to the next one.

(No) Tillage. Do not work infested fields when they are wet because more mud will stick to equipment and could be transported to clean fields. Note that fertilizer banding in the fall will move some soil. Growers will want to be conscious of clubroot when bringing in rented applicators and when NH3 nurse tanks are delivered. Perhaps clean the applicator before bringing it to the farm and take nurse tank deliveries at a fixed location at the edge of the field. When choosing a delivery location, perhaps avoid the main field entrance if possible since it will be one of the highest risk areas for potentially spreading clubroot to other fields.

Talk. If clubroot is found for the first time, report it to your neighbours and county or municipal office. As noted in discussions at the International Clubroot Workshop, people need to realize that clubroot is the “bad guy” here. Farmers who discover clubroot early and take action should be commended. Read our Top 10 from the ICW.

Source: Canola Watch

Scouting for Fusarium Head Blight Symptoms in a Developing Crop

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Premature bleaching of infected spikelet in wheat. Picture courtesy of Kelly Turkington, AAFC.

Scouting for fusarium head blight (FHB) symptoms is key to realizing whether a field is a candidate for the application of a FHB plan. Neil Whatley, crop specialist at the Alberta Ag-Info Centre, explains its importance and what to look for when scouting.

Fusarium head blight is a fungal disease of cereal crops that affects kernel development. “While caused by one or more species, Fusarium graminearum is considered the most important FHB species due to its aggressiveness and production of a toxin called deoxynivalenol (DON),” says Whatley. “This mycotoxin is a fungal chemical that affects livestock feed, the baking and milling quality of wheat, and the malting and brewing qualities of malt barley. Canadian Grain Commission grading standards allow very little tolerance of Fusarium damaged kernels (FDK) in the top grades of cereals.”

Whatley says that to limit the impact of FHB, grain producers must use a combination of disease management strategies throughout the growing season. “The first step in this strategy is realizing whether the disease is present in a developing crop by searching for disease symptoms. Additionally, learning whether Fusariumgraminearum is the dominant FHB species under observation and becoming aware of its prevalence and severity contribute to this first step toward potentially reducing its negative impact.”

FHB symptoms become visible in a cereal crop during the later heading stage. While disease infection takes place a few weeks prior at the flowering stage, symptoms appear when the plant reaches the late milk to early dough stage. “For spring seeded cereals, this typically occurs during the last part of July or early August,” explains Whatley. “Once symptoms are present, it is too late to apply a fungicide, however, this information is valuable for your FHB disease management plan in subsequent growing seasons.”

The most apparent FHB disease symptom in wheat is premature bleaching of one or more infected spikelets in the cereal plant’s head, which is visibly apparent on green heads. Orange, pink or salmon coloured fungal growth may also appear at the base and edges of the glumes on these blighted head parts. Symptoms in barley are much less distinct and the brownish discolouration of FHB infected barley spikelets can easily be confused with hail damage or the extended symptoms of other barley diseases like spot blotch, i.e. kernel smudge.

“If these symptoms are observed in a field, send the suspicious looking cereal head samples to a laboratory,” notes Whatley. “Several private seed company labs offer FHB testing services and the only way to confirm whether the affected heads contain FHB infection is to have them tested by a lab. Additionally, a lab test will determine whether the Fusarium species is indeed Fusarium graminearum or one of the less damaging fusarium species.”

Infection timing determines the severity of kernel damage. Explains Whatley, “While infection occurring at early flowering can lead to complete abortion of kernels, fusarium damaged kernels generally result from infection that occurs from the early to mid-flowering stages. Later infections that occur well after flowering and up to the soft dough stage of kernel development may not show visible symptoms. However, kernels may contain the fungus, and more importantly, the mycotoxin it produces.”

For more information about scouting for FHB symptoms, contact the Alberta Ag-Info Centre at 310-FARM (3276).

Source: Alberta Agriculture and Forestry

Increasing Numbers of Weeds are no Longer Responding to Herbicides

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Weed resistance to herbicides has been an issue in crop production for many years. However, it is is coming to the forefront as increasing numbers of weeds are no longer responding to herbicides.

“Most producers are aware of the issue but, unless it affects them directly, don’t see it as a huge issue,” says Harry Brook, crop specialist with Alberta Agriculture and Forestry. “For example, resistance to glyphosate – commonly known as RoundUp – is found in other parts of the world and Canada. We also now have glyphosate resistance in kochia in southern Alberta and it continues to spread. These should serve as a wake-up call to producers to the importance of rotating different herbicide groups when treating problem weeds. Failure to take this problem seriously will eventually result in the loss of our most popular weed control products.”

Herbicide resistant wild oats can be found in many field in the province. Some biotypes are resistant to more than one herbicide group.

“In Manitoba in 2016, 78 per cent of fields sampled had some group 1 resistant wild oats. The majority of herbicides used for wild oat control are in this group. If wild oats is resistant to a single herbicide in a chemical group, it’s pretty well resistant to all the herbicides that use that particular mode of action. Also in 2016, group 2 resistant wild oats was found in 43 per cent of Manitoba fields, and 42 per cent had wild oats resistant to both group 1 and 2. These numbers would be similar in Alberta. Soil-applied wild oat control is in group 8, which is older chemistry and has seen a resurgence in use. Cases of resistance to group 8 herbicides is increasing, despite it not being used much in the last 20 years.”

Cleavers, kochia, chickweed, spiny annual sow thistle, hemp nettle, green foxtail, wild mustard, smartweed, Russian thistle and stinkweed have all developed resistances to group 2 herbicides, says Brook. “That group contain the sulfonylureas, the “imi’s” and florasulam. Weed surveys from 2014 to 2017 estimate about 7.7 million acres or more in Alberta have some weed resistance issue.”

Brook says there are a few ways to detect a herbicide resistance issue. “Investigate areas in the field where weed control didn’t occur. Rule out other factors that might have affected herbicide performance including misapplication, spray misses, unfavourable weather conditions, and misapplication of herbicide at wrong leaf stage or late weed flushes. Other warning signs include other weeds listed on the herbicide being controlled adequately, patchy control with no reasonable explanation, a history of herbicide failure in the same area, lack of signs of herbicide injury on plants, and finally, a history of using the same herbicide group on the land, year after year.”

Brooks says when a producer uses the same herbicide or products using the same mode of action, they are actually helping select for those plants that are either not affected or affected less by the active ingredient than other plants. “By killing off susceptible plants, you are actually setting the stage for the resistant ones to thrive as all their competition is killed off.”

Herbicides that have one specific mode of action are most likely to develop resistant weeds. “Group 1 and group 2 herbicides fall into this category,” says Brook. “However, the most important reason for having resistance show up is due to repeated use of the same chemical. Short crop rotations and a lack of crop variety has set up the conditions to encourage weed resistance to emerge.”

Canada has reported resistance issues in weeds to at least six different herbicide groups. “If we ignore the risk of developing resistances, the day may come when we might lose some of our best herbicide tools from the weed management tool box. Pay attention. Scout your fields. Keep field records. Use a good crop and herbicide group rotation to keep this problem at bay. The consequences of not doing so are not cheap or pretty.”

For more information about herbicide resistance, contact the Alberta Ag-Info Centre at 310-FARM (3276).

Source: Alberta Agriculture and Forestry

Clubbing Clubroot

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Photo: Janet Kanters

On the Prairies, clubroot appeared in Alberta in 2003, in Saskatchewan in 2008 and Manitoba in 2013. As any grower can tell you, it’s a nasty canola disease that usually worsens in a field every year, partly because the spores are very easy to spread and so hardy they can survive for up to two decades in the soil. Combine this fact with the strong prices that canola fetches these days – widely encouraging back-to-back or two-year rotations – and you have a big problem.

Companies are certainly moving as quickly as possible to produce seed with effective resistance to clubroot, but breeding to defend against this particular pathogen involves navigating a wide range of complex challenges.

“Clubroot has a very short lifecycle resulting in several generations per season,” explains Dr. Marcus Weidler, vice president of seed operations at Bayer CropScience, “enabling the pathogen to react to changes in its environment very quickly, including new crop resistance genes.”

Dr. Jed Christianson, pathology lead at Monsanto Canada, explains that clubroot’s large and quickly-adapting population sizes means that it takes relatively long canola rotations of three or four years to see significant drops in the number of viable spores in the soil, and very long rotations of over 10 years for spores to effectively disappear.

“Each gall produced on a canola root can contain billions of spores,” he says. “So, given the numbers of spores generated, even very rare events like the emergence of individual spores that have gained the ability to infect resistant canola will happen over a fairly short number of cropping cycles. A one in a billion event doesn’t seem that unlikely to happen when you’re given 20 billion chances.”

Combine this with the fact not all clubroot pathotypes (races) have been identified, and it’s therefore difficult, explains Weidler, to develop a canola variety that is resistant to all potential pathotypes to which a plant may be exposed.

Dr. Igor Falak reminds us that it was in 2013 that a new clubroot pathotype was identified, one to which all canola varieties on the market carrying resistance to the original 2003 pathotype were susceptible. Although hybrids with the initial type of resistance continue to hold their own on most infested acres, the number of fields with the new pathotype is increasing annually. Falak, senior research scientist with Corteva Agriscience, blames this situation on “years of canola-on-canola.”

In addition, he notes that although clubroot “is similar to another disease of canola (blackleg), where canola products may carry race specific resistance,” clubroot-resistant canola varieties “do not have ‘fallback’ resistance mechanisms, unlike blackleg-resistant products that also have a different type of stable resistance.”

More breeding challenges are found in the fact that because canola plants carry no clubroot resistance genes, all the major seed companies are actively testing resistance genes found in rutabaga, cabbage and turnip. However, Weidler notes that because these species are only remotely related to canola, it’s far from easy to transfer genes between them without also transferring additional unwanted genetic “baggage” that negatively impacts yield, canola quality or agronomics.

If all this wasn’t enough, clubroot is a challenging organism to deal with, having unique characteristics – described by Weidler as a form of life “somewhere between a bacterium and a fungus.”

Christianson concludes that the biggest challenge in creating clubroot-resistant canola seed is to introduce resistance “while continuing to improve hybrid performance for yield, maturity, standability, resistance to other diseases, harvestability, seed quality and all of the other attributes that are important to growers’ success.”

Breeding Steps to Develop Clubroot-Resistant Canola Seed

Christianson says the steps involved in breeding clubroot-resistant varieties are relatively simple, and that any breakthroughs relating to resistance genes “are really just the discovery and characterization of more of them through concerted screening efforts.”

The entire process is a matter of crossbreeding canola with resistant relatives through normal pollination procedures and recovering offspring that are clubroot-resistant. “Those offspring then have to be crossed with canola again and again through many generations, selecting the resistant offspring at each generation for use in the next cycle to obtain plants that maintain resistance, but have recovered the characteristics of high-performing canola,” Christianson explains.

Weidler adds that unwanted genetic material from the resistance donor that negatively impacts the agronomic performance of the offspring is removed through several crossings of the offspring with elite parent stock. “Using molecular breeding tools, we can check the progress towards the end goal,” he notes. “Ideally, only the genetic sequence conferring clubroot resistance has been transferred and no other parts of the donor genome remain in the offspring.”

Breeding Progress

DowDupont was the first company in Canada to market clubroot resistant hybrids in 2009 (45H29).

“Our hybrids have multi-source and multi-race resistance to clubroot, and have a high level of resistance to the most prevalent clubroot race – race 3 – along with resistance to races 2, 5, 6 and 8,” Falak notes. “We have five hybrids with clubroot resistance: 45H29, 45H33, 45CS40, 45CM36 and 45H37. Pioneer hybrid 45CM36 is one of our newest products that contains a new source of clubroot resistance that confers resistance to both the initial type and new pathotypes, and can be rotated with the original resistant hybrids.”

Hybrid 45CM36 was launched in 2017 and is widely available to western Canadian famers for the 2018 growing season.

For its part, Bayer CropScience has “identified several new potential resistance sources,” says Weidler, “and we have been able to demonstrate that these are different from what is currently on the market.”

Christianson says that as Monsanto nears “actual commercial entry into the marketplace, we will have more to share about how second-generation resistance fits in with existing resistance traits to provide a sound disease management strategy.”

No matter what resistant canola varieties are marketed, no company can predict how long a new variety will last before it’s compromised. This depends on too many factors, explains Weidler, including the resistance gene, environmental conditions and management practices.

All the companies strongly agree that the existence of varieties with resistance is only part of the clubroot solution.

Weidler emphasizes the importance of an integrated disease management approach for clubroot, and fully supports the recommendations of the Canola Council of Canada.

Falak and Christianson echo the sentiment. “All resistance traits will be effective for longer periods of time if they are used judiciously,” says Christianson. “Choosing resistant seed is only one part of a successful disease management strategy. Growers need to include crop rotation, field scouting and early detection of clubroot, and minimizing soil movement between fields on equipment.”

Falak agrees. He says following a proper canola rotation as well as rotation of resistance genes, combined with preventing soil movement and other agronomic measures “would enable sustainable clubroot management that would prolong efficacy of any new resistance sources that are introduced.”