Tech Notes Issue 2

Strobilurin (QoI) Fungicides

Strobilurin fungicides trace there origions to a fungal antibiotic 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 woods. Over the years researchers enhanced the natural strobilurin synthetically leading to the class of fungicides known as strobilurins.

Widely used in Agriculture, it was not until 1997 when the first one, azoxystrobin, was  registered for turf use in the USA. Since azoxystrobin, additional fungicides in this class have been released in the turfgrass market including fluoxastrobin, pyraclostrobin, and trifloxystrobin.

Although these fungicides are commonly called strobilurins, they are more properly referred to as Q_oI fungicides. For those of you who may not be familiar with the Q_oI terminology, the Q_o is part of the Q-cycle found in mitochondrial respiration (cytochrome system where electron transport occurs. Q_o is the binding site for ubiquionone, which acts as an electron acceptor in this process). These fungicides inhibit fungal respiration by attacking the site Q_o in the cytochrome system of the mitochondria.

The Q_oI fungicides have a wide spectrum against a number of turfgrass diseases. Although Q_oI fungicides have similar mode of action, they do differ in regard to the molecule itself, leaf absorption and transportation within the plant, and diseases controlled. Due to the broad spectrum control properties and high level of efficacy, these fungicides have been well received and are now widely used by golf course superintendents. When applied correctly they are extremely effective and an integral part of any fungicide program.

The Q_oI fungicides mode of action however is highly specific; and for this reason the potential for fungal resistance to occur is high. With the  upcoming winter disease season almost upon us, it is important to be aware of the potential for resistance and know that certain rules need to be followed when incorporating Q_oI 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:

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 Q_oI fungicide applications to no more than ¹/₃  of the total number of fungicide applications per season.

3) Use pre-mixtures or tank mixtures of Q_oI fungicides with a different mode of action group. HEADWAY MAXX is a recent example of a pre-formulated combination of a strobilurin  (azoxystrobin) and an unrelated mode of action fungicide  (propiconazole).

4) Make preventative applications to keep disease pressure low.
Contact Syngenta for help with a targeted prevention GreenSure Plan.