Field Insights Blog | GreenCast | Syngenta
Field Insights Blog | GreenCast | Syngenta

Strobilurins: A Retro Look Back

This week, I’ve been contemplating a lecture for my class. The classroom I teach in has all the modern technology and tools to present really impressive lectures. Unfortunately, when I was a student the classroom, technology we had was non-existent. We were lucky to have a blackboard. Given that I still have a slide projector and slides I’m constructing a retro lecture for the purpose of letting students know what a lecture use to be like.

My lecture is on a general overview of fungicide classes. As I was looking through my slides, I came across a series of slides on azoxystrobin. I thought it might be worth blogging about this group of fungicides as a kind of retro look. To add a little ambience to the blog, I thought I would add (gringe) some of the slides I’m going to use in the lecture. You will note we have come a long way in lecture presentations.

German scientists discovered the original strobilurin in 1977. Named initially strobilurin A, this fungal antibiotic was produced by the pine cone fungus Strobilurus tenacellus. It’s believed that this wood rotting fungus, and similar fungi, produced strobilurin to help protect it from microbes present in the wood. Over the years, researchers enhanced the natural strobilurin synthetically leading to the class of fungicides known as strobilurins. It was around 1996-1997 when the first one, azoxystrobin, was registered for turf use as Heritage® fungicide

Although I've been referring to this group of fungicides as strobilurins, they are more properly referred to as QoI fungicides. For those of you who may not be familiar with the QoI terminology, the Qo is part of the Q-cycle found in mitochondria respiration (cytochrome system where electron transport occurs. Qo is the binding site for ubiquionone, which acts as an electron acceptor in this process). These fungicides inhibit fungal respiration by attacking the site Qo in the cytochrome system of the mitochondria. The end effect is energy in the form of adenosine triphosphate (ATP) is not produced.

QoI fungicides have a similar mode of action, but they do differ in regard to the molecule itself, leaf absorption and transportation within the plant, and diseases controlled. When applied correctly they are extremely effective and an integral part of any fungicide program.

From a plant health perspective some of the QoI fungicides exhibit growth enhancing effects separate from disease control. Although not as well documented on turf, some of the effects include hormonal changes in the plant resulting in delayed senescence, and in some cases exhibiting reduced water loss by the plant.


​​​​​​​The QoI fungicides mode of action however is highly specific; and for this reason the potential for fungal resistance to occur is high. With the upcoming disease season approaching it is important to be aware of the potential for resistance and know that certain rules need to be followed when incorporating QoI fungicides into a disease control program. The guidelines for reducing the likelihood of resistance to QoI fungicides as outlined by the Fungicide Resistance Action Group (FRAC) are summarized below:

  1. Use integrated pest management and cultural practices to reduce disease pressure. If disease pressure is low fewer applications are required and a rate more closely associated with the minimum labeled fungicide rate is more likely to be used.
  2. Limit the number of QoI fungicide applications to no more than 1/3 of the total number of fungicide applications per season. For turf this is generally in the range of two to four applications per year.
  3. Every application should be rotated with a different fungicide from a class where the resistance risk is low to medium.
  4. Use pre-mixtures or tank mixtures of QoI fungicides with a different mode of action group. Generally, the minimum labeled rates of each fungicide in the tank mixed should be used.
  5. Make preventative applications to keep disease pressure low.

About the author

Dr. Karl Danneberger is a professor of Turfgrass Science at The Ohio State University. Dr. Danneberger's contact information can be found here. You may also follow Dr. Danneberger on Twitter:

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