Determining Whether to Spray a Fungicide

Determining whether it is worth while to spray a fungicide for disease can be a difficult thing to asses. The first thing I always say about fungicides is you need to look at them like they are insurance. No one knows they are going to get hail, but they still get hail insurance. Maybe this is an extreme example, but it atleast gives you an idea of how these products need to be viewed. Based on my experience, if conditions are good (or under irrigation) I strongly recommend a fungicide because time and time again they atleast pay for themselves and protect yield at the very least.  I will mostly focus on cereals, but some of the notes can be used for a number of crops.

The first thing you need to look at is the conditions. Is there moisture and the proper temperatures? Typically if you have good growing conditions, you have good conditions for disease to develop. Most diseases, generally speaking, enjoy lots of moisture and that 20 degree celcius temperatures range. Also remember, when you crop canopies over, it has its own microclimate in there which can be very different from the conditions you feel when you step outside, so get out to your field and see what it is like under the canopy. Heavy dews are more than enough for disease spores to germinate. Remember to check the forecast moving forward too.

Next thing to ask is how good does your crop look? If you have a great crop coming it typically means you had/have the conditions for disease to develop, and you want to protect that crop. So keep that in mind. Where I am originally from in west central Sask, in 2010 there were great growing conditions during the year and great looking crops. The area hadn’t heard of Sclerotinia before, let alone seen it, and it moved in and had 50bu/ac looking lentil crops go less than 5bu/ac. Disease can move in fast, the guys that sprayed preventatively actually had a crop.

If your crop is wheat on wheat for example then your field is a good candidate for a fungicide application. Disease such as tan spot and septoria over winter on stubble from the previous year so the pressure is going to be even higher on those fields so go out and scout those first.

When it comes to leaf disease in cereals especially, always remember to take off some flag leaves or penultimate leaves (second from top) off and hold them up to the sun, if you see some light “pinhole” looking speckles that is the beginning of disease. You have about 8 days from the time a disease spore lands on a leaf until it has reproduced again and you see the big, yellow/brown spots on your leaves. This is when the rain splash, dew, animals etc move the spores up the leaves. I have always been told that assuming there are good disease conditions, whatever your leaf below looks like that’s what the leaf above it is going to look like in 5-7 days. So for example if you have 20% infection on the penultimate leaf, a week later there will be around 20% infection on the flag leaf.

With a “curative” fungicide such as some of the active ingredients in the group 3 triazole family (Caramba, Prosaro, etc) these products have the potential to suppress the disease up to about day 5 or 6 in the lifecycle of the disease, so if you have a lot of small pinholes on your leaves you can guarantee more are coming and it probably is best to apply a fungicide to ensure you maintain a high yield potential. Always remember it is best to spray preventativley before there signs of heavy disease pressure, once it moves in the damage happens fast.

There is also the plant health benefits some products bring to the table such as the strobilurin family of fungicides (group 11) so these can help pay for the fungicide and further help a plant yield better and fight disease. Some of these benefits include, increased nitrogen use efficiency, water use efficiency, and decreased ethylene producttion. Examples of these products include Headline and Quilt.

A great leaf disease basic formula I got from Steve Larocque`s Beyond Agronomy Newsletter is as follows to determine yield loss:

Percent Loss= .66 X % of flag leaf area infected + .50 X percent of penultimate leaf area infected divided by 2.

Example: 10% Flag leaf infection and 20% penultimate leaf infection on what looks like will be a 50bu an ac crop.

                .66 X 5% + .5 X 20% divided by 2

                = 6.65% yield loss X 50bu = 3.3 bu an acre loss

Assuming $7.50 a bushel Red Spring prices 3.3 X 7.50 = 24.75 an ac LOSS.

Note: Some leaf diseases are more aggressive than others, such as rust being more yield robbing than tan spot. This is a ball park.

Sclerotinia yield losses in canola typically look like this:

% infection divided by 2 = yield loss.

Example: 15% infection on a 40 bu an acre canola crop = 7.5% yield loss = 3 bu an ac

Using a $13 a bushel prices = 13 X 3 = 36 bushel an acre yield loss.

There are also the quality issues the diseases cause, especially with Fusairum Head Blight. You lose yield AND quality.

Always know the target disease you are going after, that way you can talk to your neighbours or local agronomists or reps about what product is going to be the most effective on what disease and at what stage. For example, just because you do not have any leaf disease, does not mean that fusarium headblight isnt going to be an issue so an application may be warranted at head emergence. Also, remember fungicides don’t last for the rest of the plant life cycle, typically after 14-21 days (depending on product) the fungicide will begin to wear off and the plants will be susceptible to disease again. Note also that spraying a fungicide after heads have begun to fill (in cereals) typically isnt economical, the disease has done most of its damage. You are just revenge spraying at that point. The flag leaf and penultimate leaf of a wheat crop combine to photosynthesize and produce upwards of 60% of the total yield so that shows how important protecting those 2 leafs are.

Always remember the disease triangle. Host, Pathogen, Environment. There needs to be all three present for disease to develop and flourish. For example if you are concerned about Fusarium Headblight in Durum then Durum is the host, if you have had FHB in the area before then the pathogen is present and if conditions are in that 20 degree range and damp for a period of time then you have the environment. This means there is a good chance your crop will have some FHB in it.

This was all over the place, I apologize, hopefully there is still something everyone could take away from it.

Excessive Moisture

There are some places across the Canadian Prairies that are seeing above average rain fall and therefore some laying water in the fields. Rain is almost always a good thing, but there are times when it can be detrimental to yield.

The first thing excessive rainfall does, as many are aware, is cause leaching of soil mobile nutrients. The 3 most mobile nutrients being Nitrogen, Sulfur and Boron. The lighter (sandier, lower CEC) the soil, the more nutrients will move. For example, for every inch of moisture accumulated, nitrate nitrogen (plant available) can move downwards of 10” in the soil profile of a sandy soil! This tends to be only about 3” for every inch of rain in a clay loam soil.

Another problem you run into is denitrification. This is caused by conditions where there is a lack of oxygen in the soil (anaerobic conditions), so microbes essentially begin to breakdown and use the nitrate. Once soils get very saturated these organisms tend to already be active and begin the process of denitrification more readily the next rainfall. This on top of leaching can cause for large amounts of Nitrogen losses.

When it comes to herbicide breakdown there can be issues with excessive moisture as well. Usually, we see a more rapid breakdown of residual herbicides under good moisture conditions, but to much moisture can cause herbicides not to be broken down and put you into the same situation you might run into under excessive drought situations. This is due to soil microbes that break down residues not being active under flood situations, essentially the microbes start to drown. This can keep residues around longer and cause some injury to your canola after Pursuit (imazethapyr).

Anaerobic soil conditions lead to other issues in many crops as well. In your pulse crops you will see a significant reduction in nodules on your roots, therefore a reduction in nitrogen fixation (lots of moisture steals nitrogen a number of ways!). This is again due to the bacteria not being able to survive under excessive moisture. You will also notice decreased root hairs and mycorrhizae fixations in crops like flax which will hinder yield.

 The next thing you will see is typically a yellowing and purpling of the plants whether it be canola, lentils or wheat. The reason for this is due to plant stress and because roots struggle to grow and take up nutrients, so partly what you are seeing is some early macronutrient deficiencies such as phosphorous, nitrogen or sulfur.

Even though most organisms tend to be negatively affected by excessive moisture, you will see root rots and diseases caused species such as pythium and rhizoctonia. These diseases prefer wet conditions and can cause significant yield loss.

After all of this you end up with a weaker plant and therefore a plant more susceptible to other types of disease (rusts, white mould etc) and conditions that are favourable for their development. Even once it dries up a bit you still are not out of trouble!

Canola is typically seen as the best at surviving flood situations. In my experience Invigor varieties seem to be even more superior than RoundUp Ready. I have seen canola be under water for up to 5 days without significant yield loss, and even seen upwards of 10-14 days, but this is where you begin to see significant yield reductions (40%+). Wheat is very good at tolerating the water as well with minimal reductions in yield even at 2-4 days under water, beyond that I have not experienced, but can imagine yields would begin to drop off. Barley is slightly worse than wheat tolerating upwards of 3 days. Flax is next followed by lentils and peas which are very sensitive to flooding, seeing yield reductions even after 24 hours. If you get into your crops that prefer warmer temperatures then you run into even more issues, like with corn, dry beans and soybeans. The rain typically means cooler temperatures, less sunlight and cooler soil temperatures which these crops extremely dislike. Corn can see yield reductions of up to 35% in under 72 hours.

At the end of the day I really like Luke Bryan’s song “Rain is a Good Thing”, but in some instances it most definitely is not a good thing.

Deciding on a Foliar Fungicide

Fungicides are options for all growers crop input arsenal. There are a number of stages where fungicides are generally applied, typically targeting different diseases, especially in cereals. Determining when is the best time to spray can be difficult, but you need to identify the main disease you are going for. With fungicides typically being in short supply, it is best to make a decision early and book the product you need at your local retailer.

I am going to start off talking about pulses. When it comes to pulses, the 2 main time when you will apply a fungicide is with your herbicide, typically something like Headline from BASF is sprayed if there are any fungicides applied with herbicides in pulses. This is to keep diseases like ascochyta slowed down until flowering when you can go in with another fungicide application. If using a product strobilurin fungicide you will also see some plant health benefits that include increased N use efficiency, water use efficiency, decreased ethylene production and a grocery list of other benefits. The next time that is typical for a fungicide application is from beginning of flowering up until about 50% flower, under high disease years there may be a need for other application beyond this stage. Products like Quadris (azoxystrobin) from Syngenta and Headline (pyraclastrobin) from BASF are very good options for ascochyta, if anthracnose is what you’re after then Quilt (azoxystrobin and propconizole) from Syngenta and Headline again are very good options. (Note: Quilt isn’t registered on ascochyta, but I have seen it do a relatively good job at holding the disease back in lentil). If you are concerned about Botrytis and sclerotinia (white mould) then Lance (boscalid) from BASF is a great option, or you can go for the heavy hitter fungicide Headline DUO which is Headline and Lance and get a whole spectrum of pulse diseases. If you are strictly going for sclerotinia then Lance is your soul registered option in lentils, or peas, but in a crop like Beans you have options such as Allegro from Syngenta. There is Serenade (bacillus subtilis) , a bio fungicide from UAP as well.  In the coming years there looks to be a couple new options becoming available from companies like Bayer and BASF that are apart of group 7 fungicide class (SDHI’s) that are looking very promising.

Note: There are some other fungicides for pulses out there such as Proline (prothioconazole) from Bayer, but is used in limited amounts on pulses due to its lack of activity on a number of diseases and price.

When it comes to canola the first option you have for a fungicide is to hit it with your incrop with a full rate of Headline. This is going to decrease blackleg infestations as well as give the plant some added health benefits as discussed earlier. When it comes to 20%-50% flower this is the time you are going to be aiming for control of sclerotinia. There are a number of products out there to help combat this disease, they include; Proline, Astound (cyprodinil,fludioxinil) from Syngenta, Lance, Quadris, Rovral (iprodione) and Serenade. The products that are used most in my experience tend to be Proline and Lance. Astound is a newer product, but shows potential, especially if you do any reading on 3^rd part research on the disease and fungicide controls. There is a new option this year from Dupont called Vertisan (penthiopyrad) which may be an option for you to try as well. Most of these products will do a good job, it may come down to what you feel comfortable with, fits into your programming or is easiest to get your hands on. Doing side by side trials is a great option to see which one works best for you.

Wheat is the tricky one. The first option you have again is at in crop timing to tank mix Tilt (propiconazole) with your herbicide. These typically can give you a good start on decreasing leaf disease levels if there is an early infestation, especially if you are later spraying your crop (5 or 6 leaf). I have read some research showing half rate Tilt had very little difference in efficacy vs full rate. This typically will give you 7-14 days protection. Spraying a product like Stratego (trifloxystrobin and propiconazole) from Bayer with your in crop herbicide can cause it to heat up the herbicide and cause crop damage, this is due to the strobilurin portion, watch spraying any strobilurins with your herbicide tank mixes. The next time to spray a fungicide on cerals is flag leaf stage. The flag leaf and penultimate leaf can combine to contribute for upwards of 70% of total yield, so protection of these 2 leaves is very important. If you are trying to control a disease such as stripe rust then there are a number of options including Folicur (tebuconazole) from Bayer which has very strong activity on rust, Caramba (metconazole)which is also strong on rust and Quilt which is strong on rust as well and provides increased length of protection as well as some better systemicity. The new Twinline fungicide from BASF is a combination of Headline and Caramba and should offer very good activity on rust as well as on other leaf diseases. If you are simply trying to control septoria, tan spot, spot blotch etc. then there are a number of options including all the fungicides I have stated previously. Products like Quilt and Headline are going to have some added plant health benefits due to the family of fungicide they are, so good to take that into account as well. When it comes to fusarium headblight control in my eyes the top two products are Prosaro (tebuconazole and prothioconazole) from Bayer and Caramba. The group 3 triazole family of fungicides has very good activity on fusarium species diseases. Both of these products are very good, in my research there are slight differences though. Prosaro has 2 ingredients, one which is faster acting (tebuconazole) and one which provides longer control (prothioconazole). The research I have done consistently shows that Prosaro has the slight edge in actual suppression of the disease, while Caramba has the slight edge in actual DON levels on the kernels (DON is the mycotoxin produced by FHB infection) based on the fact it is better at decreasing colonization of the bacteria that produce the mycotoxin. Leaf disease is strong with these products as well.

Choosing a fungicide can be tough, but go in and ask questions about your specific situation at your local retail and they should be able to give you the answers you need to make an informed decision.

I didn’t break down every fungicide in depth as I would have liked, but if you have any questions on specific ones feel free to ask and I should be able to give you some information to help.