No. 2 Article 4/April 8, 2011

Providing Some Clarity on Fungicide Products

As the growing season approaches, we see more and more advertisements for foliar fungicides. Several new products have come onto the market, which has created confusion about the active ingredients in various products as well as what products are registered for use on particular crops. I hope to provide clarity about both product active ingredients and the amount of active ingredient(s) applied.

As shown in Table 1, the most popular foliar fungicides used on field crops contain an active ingredient from either the triazole or the strobilurin fungicide class, or from both. Fungicides in the triazole and strobilurin fungicide classes differ in their mode of action on pathogenic fungi and their movement within the plant. Some key aspects of each fungicide chemistry class are described below.

Table 1. Incomplete lista of fungicide premix products, solo strobilurin products, and solo triazole products registered for use on field crops in Illinois.

Product (company)

Typical use rate per acre

Triazole fungicide and rate (lb a.i./A)

Strobilurin fungicide and rate (lb a.i./A)

Crops registered for use onb

Quilt (Syngenta)

14 fl oz

propiconazole, 0.11 lb

azoxystrobin, 0.07 lb

Corn, soybean, wheat

Quilt Xcel (Syngenta)

10.5 fl oz

propiconazole, 0.08 lb

azoxystrobin, 0.10 lb

Corn, soybean, wheat

Quadris Xtra (Syngenta)

5 fl oz

cyproconazole, 0.03 lb

azoxystrobin, 0.07 lb

Soybean

Stratego (Bayer CropScience)

10 fl oz

propiconazole, 0.08 lb

trifloxystrobin, 0.08 lb

Corn, soybean, wheat

Stratego YLD (Bayer CropScience)

4 fl oz

prothioconazole, 0.03 lb

trifloxystrobin, 0.10 lb

Corn, soybean

Headline AMP (BASF)

10 fl oz

metconazole, 0.04 lb

pyraclostrobin, 0.10 lb

Corn

Evito T (Arysta Life Science)

4 fl oz

tebuconazole, 0.07 lb

fluoxastrobin, 0.05 lb

Corn, soybean

TwinLine (BASF)

7 fl oz

metconazole, 0.04 lb

pyraclostrobin, 0.06 lb

Wheat

Absolute (Bayer CropScience)

5 fl oz

tebuconazole, 0.09 lb

trifloxystrobin, 0.09 lb

Wheat

Headline (BASF)

6 fl oz

 

pyraclostrobin, 0.10 lb

Corn, soybean, wheat

Quadris (Syngenta)

6 fl oz

 

azoxystrobin, 0.10 lb

Corn, soybean, wheat

Evito (Arysta Life Science)

2 fl oz

 

fluoxastrobin, 0.06 lb

Corn, soybean, wheat

Gem (Bayer CropScience)

3 fl oz

 

trifloxystrobin, 0.10 lb

Soybean

Tiltc (Syngenta)

4 fl oz

propiconazole, 0.11 lb

 

Corn, soybean, wheat

Folicurd (Bayer CropScience)

4 fl oz

tebuconazole, 0.11 lb

 

Corn, soybean, wheat

Proline (Bayer CropScience)

3 fl oz

prothioconazole, 0.09 lb

 

Soybean, wheat

Prosaro (Bayer CropScience)

6.5 fl oz

prothioconazole, 0.09 lb
tebuconazole, 0.09 lb

 

Wheat

Caramba

10 fl oz

metconazole, 0.06 lb

 

Wheat

Topguard (Cheminova)

7 fl oz

flutriafol, 0.06 lb

 

Soybean

Domark (Valent)

4 fl oz

tetraconazole, 0.06 lb

 

Soybean

Alto (Syngenta)

4 fl oz

cyproconazole, 0.03 lb

 

Soybean

aAdditional fungicide products not included in this table may be registered for use on field crops in Illinois. Inclusion here should not be viewed as a recommendation of a particular fungicide over one not included.
bRegistered on crops as of March 30, 2011. Some products may become registered for use on additional crops at a later time. Always read the label to be sure.
cThe active ingredient in Tilt (propiconazole) is now off-patent, and other products are available that contain propiconazole. It is important to read the label of any propiconazole product to ensure that it is registered for use on a specific crop.
dThe active ingredient in Folicur (tebuconazole) is now off-patent, and other products are available that contain tebuconazole. It is important to read the label of any tebuconazole product to ensure that it is registered for use on a specific crop.

Strobilurin fungicides. The technical name for the strobilurin class of fungicides is the quinone outside inhibitors (QoI). This group includes active ingredients such as azoxystrobin, fluoxastrobin, pyraclostrobin, and trifloxystrobin. Strobilurin fungicides inhibit the respiration of fungi. In addition, strobilurin fungicides are most effective at inhibiting fungal spores from germinating. They can inhibit mycelial growth of the fungus as well, but inhibiting spore germination is what they do best. Strobilurin fungicides have limited movement (systemicity) in the plant. They can have translaminar movement (across the leaf), but only azoxystrobin and fluoxastrobin move within the xylem of the plant. Strobilurin fungicides tend to accumulate in the cuticle layers of the leaves. Because of their high efficacy in inhibiting spore germination and their tendency to accumulate in the cuticle layers of the leaves, strobilurin fungicides work best when applied preventatively--prior to pathogenic fungi penetrating the leaves and growing throughout the leaf cells.

Triazole fungicides. The technical name of this class of fungicides is the demethylation inhibitors (DMI). This group includes active ingredients such as metconazole, propiconazole, prothioconazole, and tebuconazole. Triazole fungicides inhibit ergosterol biosynthesis in pathogenic fungi. Because spores already contain ergosterol, the triazole fungicides are generally not very effective in preventing spore germination. Triazole fungicides work best by inhibiting fungi's mycelial growth. In general, the triazole fungicides tend to be absorbed and move more quickly within the plant than the strobilurin fungicides. Triazole fungicides move through the xylem of the plant (upward movement only). Because of their ability to inhibit mycelial growth and their movement through the xylem, triazole fungicides may have some postinfection activity on fungi--some people refer to this type of activity as "curative." It should be noted that this activity actually does not cure anything--it simply means that the fungicide has the ability to inhibit a fungus that already has entered the plant.

"Curative" vs. "preventative" fungicides. In the world of marketing, triazole fungicides seem to have become synonymous with so-called curative fungicide, and strobilurin fungicides with so-called preventative fungicide. The fact is that in some cases, the strobilurin fungicides can have "curative" activity and the triazole fungicides can have "preventative" activity, so it's important not to get too wrapped up in the two categories.

Solo vs. combination a.i. products. I often get asked if there are advantages to using products with a premix of triazole and strobilurin fungicides over those with one or the other alone. The general advantages of using products with a triazole-strobilurin mixture are these: a broader range of pathogen species may be controlled; fungicides may accumulate and move into different plant tissues; and the risk of selecting fungicide-resistant variants of fungal pathogens may be reduced. These advantages especially hold true when the amounts of fungicide active ingredients (lb a.i./A) in the premix are similar to the amounts when applying the solo products. In other words, how similar is the rate, per acre, of the strobilurin active ingredient in the premix vs. the rate of the same strobilurin fungicide in the solo product?

Comparing amounts of active ingredient among premix products. Other questions that I have received recently deal with the actual amount of strobilurin active ingredient or triazole active ingredient in one premix product vs. another. Even though two particular fungicide active ingredients are in the same fungicide class (for example, azoxystrobin and pyraclostrobin), inherent differences between them do exist. For instance, 1 gram of azoxystrobin may not be equal to 1 gram of pyraclostrobin in the ability to inhibit a fungus. It is thus very difficult to compare two premix products solely on the amount of strobilurin or triazole active ingredient they contain unless their ingredients are identical. A better comparison would be between the amounts of strobilurin and triazole active ingredients in the premix product and the amounts of the same strobilurin and triazole active ingredients that would be applied with the solo products.

Disease control effects vs. physiological fungicide effects. In some cases, foliar fungicides may have effects on plants other than disease control. The strobilurin fungicides, especially, have been researched for their potential physiological effects. Peer-reviewed scientific articles have been published documenting that in greenhouse and laboratory studies, strobilurin fungicides can have physiological effects on plants. These published effects include delayed senescence, altered amounts of plant hormones, increased activity of antioxidative enzymes, and increased activity of nitrate reductase. Although these effects have been documented in greenhouse and laboratory studies, they have not been reported from field research studies. In addition, the link between these potential physiological effects and grain yields has not been reported.

The disease control effects of fungicides have been well documented in field studies, and the consistency of profitability from fungicide applications increases as disease pressure increases. In University of Illinois corn fungicide trials conducted from 2008 to 2010 across several locations in the state, the average yield increase from foliar fungicides in seven environments with low disease pressure was 0.1 bu/A. Conversely, the average yield increase from foliar fungicides in eight environments of moderate to high disease pressure was 15.4 bu/A. These results tell us that fungicides should be applied to crops based on disease risk and scouting observations, not the potential physiological effect that may or may not occur and may or may not affect yield.

In summary, I would note these key conclusions:

  1. Foliar fungicide products differ in their active ingredients, but gram-per-gram comparisons of active ingredients are not always appropriate. Specific ingredients may have inherent differences even if they are in the same fungicide class.
  2. There are potential advantages to using products that contain fungicide active ingredients from two different fungicide classes.
  3. Achieving consistent economic benefits with fungicides is more likely when applications are made based on disease risk and scouting observations. This is a more profitable approach than applying a fungicide in hopes of achieving a yield increase based on potential physiological (non-disease control) effects on the plant.

--Carl A. Bradley

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