Diseases
Dr. Kelly Turkington discusses considerations to spray a fungicide, recommendations for Fusarium head blight in cereals and how to get the most out of your cereal fungicide applications. 

Click here for the full summary of Dr. Turkington’s presentation.

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Crop rotation is an important tool for our first line of defence in Western Canada. From a pathologist’s perspective, a wheat-canola-wheat-canola rotation – a single year between host crops – is not long enough to realize one of the benefits of rotation and allow decomposition of any infested crop residue. 

Variety resistance is also an excellent tool. When you have a variety with good levels of resistance, you really don’t need to spray a fungicide. The problem is that in your field you’re facing a range of diseases and it’s been very difficult to get varieties that have good levels of resistance to absolutely every disease issue that you might have in that field. If you have a tight rotation, your variety may not have the package of resistance that you need and, as a consequence, you will start to rely on fungicides. 

We like to use the disease triangle to express what a disease is all about. It’s the result of a susceptible host, a favourable environment and sufficient quantities of a virulent pathogen. The key thing to remember is that what you do in terms of crop management practices will impact the interaction of those three factors and ultimately, the risk of disease. 
Disease triangle
The disease triangle. Source: Dr. Kelly Turkington

Interation of fungicides with variety resistance
At a trial in Melfort, Sask., three barley varieties rated susceptible (Sundre), intermediate (Chigwell) and with a good resistance package (Vivar) against net-form net blotch were sprayed with Twinline (metconazole + pyraclostrobin) fungicide at the flag-leaf stage. With no fungicide application, Sundre had just under 20 per cent leaf area diseased on the penultimate leaf, but there was very little disease on Chigwell and Vivar with or without a fungicide. With a fungicide, there was a dramatic reduction in disease with Sundre.

If we look at yield, Sundre went from around 115 bushels per acre (bu/ac) without a fungicide to 145 bu/ac with the fungicide application. Chigwell had a bit of a response to fungicide application, which may be because it has an intermediate level of resistance. Vivar’s response to fungicide was basically flat. So, if you’re using a resistant variety that is giving you the protection you need, you don’t need to worry about putting on a fungicide.

General knowledge on application timing
In terms of fungicide application timing in cereals for leaf disease, it is important to know where yield and grain fill comes from. The literature suggests the wheat ear (head) contributes about 22 per cent to yield, while the flag-leaf contributes about 40 to 45 per cent, and penultimate (leaf below the flag) contributes about 23 per cent. Those are the key plant tissues that you want to protect. 

In barley, the flag-leaf is less important because it tends to be quite small in some varieties. The literature for barley suggests the head contributes around 13 per cent, the flag-leaf stem 25 per cent, the flag-leaf nine per cent and the penultimate about 20 per cent.

Overall, if you’re looking at a target as far as protecting the plant tissues that are key for grain filling and yield, the upper canopy tissues in those cereal crops are going to be your target.

Pathogen characteristics
The characteristics of the pathogen can be very important when trying to improve your ability to manage plant diseases with a fungicide. A monocyclic pathogen has one cycle of spore production, host infection and disease development, so there’s a very specific target there. Fusarium head blight (FHB) is a monocyclic pathogen.

Polycyclic pathogens cycle on the living crop more than once per growing season. These are diseases like stripe rust, tan spot, Septoria, net blotch and scald. This cycle may mean you can’t rely on a single application and may need several applications to get the level of control you desire, especially with highly susceptible varieties and under favourable weather conditions.

Stripe rust is an example of a polycyclic pathogen. It can move from spring wheat onto winter wheat seedlings in the fall. If I were advising a producer, I would note the presence of stripe rust in the fall and then be out in the winter wheat field as soon as the crop started to re-grow in the spring to see if the stripe rust fungus had survived. The stripe rust pathogen can rapidly cycle on the wheat crop: spores released from pustules on infected leaves are carried by the wind to healthy leaf tissue where they germinate, produce hyphae, penetrate plant tissue and within seven to 14 days, you’ll have symptoms – including pustules that produce a new crop of spores. So, every seven to 14 days, stripe rust can cycle on the crop well before head emergence. Thus, later on, on those upper-canopy leaves, you may see symptoms of stripe rust that can cause significant concern, especially if the disease becomes established in the crop before flag-leaf to head emergence.

Fungicide insensitivity
What about pathogen adaptation to the active ingredients in fungicides? Pathogens with a high risk of adapting to the active ingredients in fungicides have the following characteristics: they have mixed reproduction, so they reproduce sexually as well as asexually; and they also have an outcrossing system of reproduction where with they have male and female isolates – or mating types, – so you need a male and female for sexual reproduction to occur.

Sexual reproduction where different mating types are needed has the potential to create more genetic variability in the fungal pathogen, which can then be selected for when applying a fungicide. The other important thing is high genetic and pathogenic diversity in that pathogen, which increases the risk that a pathogen will adapt.

An example of a pathogen at moderate to high risk of adaptation to either plant disease resistance or fungicide active ingredients is the net blotch pathogen. In a study funded by the Western Grains Research Foundation, Alireza Akhavan, a PhD student working at the University of Alberta, found high levels of genetic/pathogenic diversity in the net blotch pathogen. It also reproduced asexually as well as sexually and with mixed mating types. Using a laboratory assay, Alireza found a few isolates that were insensitive (resistant) to Tilt (propiconazole) and, in some cases, insensitive to Headline (pyraclostrobin).

Randy Kutcher at the University of Saskatchewan is also looking at the tan spot fungus and potential insensitivity in the tan spot population.

Shifts in the fungicide sensitivity of cereal pathogens have been recognized in Europe for some time now and there have also been reports of changes in North America.

For example, in February 2015, Chris Mundt and colleagues at Oregon State University put out a disease update notice (Oregon State University, Disease Update, February 20, 2015, Chris Mundt, Mike Flowers, Nicole Anderson and Clare Sullivan), stating that, based on surveys from 2014, there were indications some fields had Septoria resistance to strobilurin (Group 11) fungicides. They also reported resistance to triazoles (Group 3) was starting to build.

Their recommendation in that part of the Pacific Northwest was to only apply a fungicide for early-season leaf disease control when stripe rust was present, because the fungicides were still effective against stripe rust. They also recommended using a succinate dehydrogenase inhibitor (SDHI) fungicide (Group 7) once per year, and for growers who did so to combine it with either a strobilurin or perhaps a triazole.

Click here to see part two: managing the tools available, including fungicide application timing trials.


This article is a summary of the presentation “Getting the Most Out of Your Cereal Fungicide: A Western Canadian Perspective,” delivered by Dr. Kelly Turkington, Agriculture and Agri-Food Canada, Lacombe, Alta., at the Field Crop Disease Summit, Feb. 21-22, 2017. Click here to download the full presentation.

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Managing the tools available
Given that fungicides are an important component of their leaf disease management programs, farmers need to manage the fungicides we have by using products with more than one active ingredient and/or rotating the products they use. [Miss part one? Click here.]

When a susceptible variety is grown and weather conditions are very favourable, farmers may be concerned about early season leaf disease development. Rather than applying a fungicide with their herbicides, one option might be to look at a seed treatment and use xylem-mobile fungicides that will move from the seed up into the leaf tissue to provide some early season leaf protection.

These fungicides are mixed with other fungicides that give us good activity on some of the root rots, whether it’s Fusarium or Rhizoctonia or Pythium and so on. Ideally, one may want to use a seed treatment with different active ingredients versus foliar fungicides that may be used later on in the season, with one application of a triazole to give us some suppression of FHB and late-season leaf disease management. 

Using a seed treatment for early season leaf disease management is food for thought and may be a strategy to consider.

Nature of a fungicide influences risk of resistance
The nature of the fungicide also plays an important role in effectiveness. Some fungicides do very well in terms of particular plant pathogen groups versus other fungicides, so check the provincial crop protection guides to make sure you are choosing the right fungicide for the disease issues you are targeting. 

The nature of the fungicide also influences the risk of fungicide resistance. Fungicides with a very specific individual target (single site activity) within the pathogen are typically at higher risk versus actives that have multiple targets (multi-site activity).

Mobility within the plant also plays a role, as it influences the efficacy, persistence and period of activity. Mobility also influences application technology, so if the product is not systemic, it will be especially critical to use practices that ensure good coverage of the plant surface you are trying to protect.

Fungicide timing and leaf spot diseases
Fungicide application timing is important for cereal leaf spot management. From 2010 to 2012, we looked at the effect of fungicide timing on leaf spot diseases in barley at 13 sites. Specifically, we compared tank-mixing a fungicide with herbicide versus putting that fungicide on at the flag-leaf stage versus using a split application, a half rate earlier on and then coming in with either a half rate or a full rate of fungicide at flag-leaf emergence.

Overall, our results indicated the best leaf disease control and the highest yields were achieved where we put a fungicide on at the flag-leaf stage and where we did not delay the herbicide application and, thus, had early weed removal. 

Table 1: Yield and herbicide/fungicide treatment
slide 33
Turkington et al. 2015. The impact of fungicide and herbicide timing on foliar disease severity, and barley productivity and quality.               Can. J. Plant Sci. 95: 525–537.

Timing also a factor in stripe rust control
Another trial, led by Kutcher and Brian Beres with Agriculture and Agri-Food Canada in Lethbridge, Atla., and conducted in Lacombe, Alta., illustrated the importance of fungicide application timing for stripe rust control in winter wheat. The most effective application for AC Bellatrix, a susceptible variety, was in the spring at the flag-leaf stage. For Radiant, a variety with some resistance, there was no need for a fungicide.

As mentioned previously, seed treatments may be an option for early- to mid-season leaf disease management. Recently, we did a set of experiments – including at Melfort – looking at the interaction of variety, seed treatment and fungicide on net blotch on barley. In 2013, we simply used a seed treatment without a fungicide and reduced the level of disease to less than 10 per cent of the leaf area affected from 30 per cent in the untreated control. If you looked at Twinline foliar fungicide applied with no seed treatment, there was very good control. Where we combined seed treatment with foliar treatment, it really didn’t improve control.

Our best yield response was where we simply put Twinline on at the flag-leaf emergence stage, whether a seed treatment was used or not. Overall, if you look at work done by research groups across Western Canada, if you have the opportunity to choose a variety that has good levels of resistance to the disease spectrum you’re dealing with, that’s an excellent tool to manage disease and will help you to avoid a fungicide application. 

However, the varieties you want grow may not have a complete package of resistance to the diseases of concern. Thus, it will be important to scout fields at or just prior to flag-leaf emergence to assess disease risk and its potential impact to determine if a foliar fungicide application is required to protect key upper plant canopy tissues. 

FHB application timing
Currently the recommendation for FHB fungicide application is to spray when you’ve got 75 per cent of the heads out of the boot – that’s when you can start – to about when you have 50 per cent of the head showing anthers in the middle part of that head. The problem with starting at 75 per cent head emergence is that 25 per cent of the heads are still in the boot. Thus, given the nature of the fungicides that we use for FHB, applications at 75 per cent head emergence will not provide much, if any, benefit for those heads not yet emerged.

Recent research from the United States suggests we may have a wider window for application post head emergence to get the most out of that fungicide application. 

Trials from the U.S. looked at fungicide timing and effect on FHB disease rating and DON content with applications at the start of anthesis (when you first see yellow anthers emerging from the middle part of the wheat head) and then either two, four or six days following the start of anthesis. Overall, results suggested that even at four and six days after anthesis, control was as good as applications at anthesis, and in some cases may actually be slightly better.

The trend was similar with DON content.

I think, in terms of getting the most out of our fungicide application for FHB, we need to look at revising our target. Maybe going a little later is something to consider so you provide protection for all heads within the crop. However, growers are cautioned that they need to follow label recommendations and the pre-harvest intervals for the products they use.

Expectations for fungicides
In terms of expectations for fungicides, it’s important to be realistic. Fungicides can certainly be effective tools for some diseases, but it’s important to use them prudently and to manage those fungicides so they remain effective tools for you over the next 10, 15, 20 years. Timing can have a huge impact. Fungicide application also doesn’t mean a completely disease-free crop and, thus, it is important to leave some check strips so that you can adequately judge fungicide performance.

Overall, farmers are encouraged not to rely exclusively on fungicides as their only defence against plant disease. Try to use the other tools in the toolbox. The more tools you have, the broader your ability to control disease and other pest and crop management issues in your crop.  By using a range of tools, including crop rotations of at least two years between host crops, you’re going to prolong the effectiveness of tools such as disease resistance and fungicides into the future.


This article is a summary of the presentation “Getting the Most Out of Your Cereal Fungicide: A Western Canadian Perspective,” delivered by Dr. Kelly Turkington, Agriculture and Agri-Food Canada, Lacombe, Alta., at the Field Crop Disease Summit, Feb. 21-22, 2017. Click here to download the full presentation.

Don't forget to subscribe to our email newsletters so you're the first to know about current research in crop management.

Top Crop Manager's Herbicide Resistance Summit has been announced! Sign up today for early-bird pricing: https://www.weedsummit.ca/event/registration
LET'S START WITH THE PAST...
In the past, disease management in field crops was largely based on major gene resistance and the use of fungicides.
Dr. Bruce Gossen discusses some of the results of his long-term cropping study and what that means for growers in Canada looking to manage crop diseases.

Click here for the full summary of Dr. Gossen's presentation.

Don't forget to subscribe to our email newsletters so you're the first to know about current research in crop management.

Top Crop Manager's Herbicide Resistance Summit has been announced! Sign up today for early-bird pricing: https://www.weedsummit.ca/event/registration
A wheat leaf rust resistance gene that’s been overcome by virulent pathogens is called a “defeated gene,” according to Brent McCallum, a pathologist with Agriculture and Agri-Food Canada. But its counterparts – resistance genes that still prove effective against pathogens in the field – are not called “victorious genes.” They’re known as “durable genes” that can be depended on for good control, year after year.
In September 2015, a corn disease called tar spot was detected for the first time in the United States. Until then it had only been known to occur in Mexico and parts of Central and South America.  
Surveys of sunflower rust in Manitoba show variations in the predominance of different races from year to year, but the overall trend is towards races with greater virulence.
If “technology transfer tool” can be defined as a way to get information into the hands of as many people as possible, weather-based disease forecasting models are the perfect example of how this works in practice.
Root rot and leaf spot diseases can be an annual problem for cereal growers, yet despite many years of cereal production in Western Canada, much is still to be learned about controlling these diseases in both organic and conventional farming systems. Research in Western Canada assessed resistance to the diseases some years ago, but much more could be done.
Although stripe rust is not a new disease, it was rarely considered an economic concern, except in some irrigated crops in southern Alberta. However, in 2011 stripe rust caused serious economic impacts in both Saskatchewan and southern Alberta. Unusually high spring precipitation resulted in high moisture conditions in spring wheat crops, which created favourable crop canopy conditions for the pathogen. Another factor was the large diversity of pathogen races that appeared in 2011, including a race virulent on Yr10, a major gene in the popular winter wheat AC Radiant. Researchers are trying to learn more about the disease and find ways to help both plant breeders and growers manage the disease.
In Saskatchewan, durum wheat growers have experienced serious losses to Fusarium head blight (FHB) in recent years. Although FHB infection was considered quite severe in 2014, infection in durum wheat crops was even worse in 2016. The weather conditions were a significant factor, but the high levels of FHB were compounded by the adoption of shorter rotations, a lack of highly resistant varieties and the availability of fungicides that only suppress the disease.
A relatively new root rot disease in pea and lentil crops is steadily expanding across Alberta, Saskatchewan and Manitoba. Caused by the soilborne “water-mould” pathogen Aphanomyces euteiches, the root rot can cause infection any time throughout the growing season under the right field conditions. Currently, longer crop rotations are recommended, but few management options are available.
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