Qol Fungicides

The Qo fungicides inhibit plant pathogens by blocking the pathogens ability to produce energy. They do this by blocking the transfer of electrons at the Quinone "outside" site of the bc1 complex (complex III in the electron transport chain). There are two other fungicidal target sites at complex III, the Quionone "inside" (Qi) site (FRAC group 21) and the Quinone "outside" Stigmatellin binding (QoS) sub site (FRAC group 45). The members of the Qo group (FRAC group 11) are cross-resistant with each other but are not cross-resistant with members of the QiI (FRAC group 21) or QoSI (FRAC group 45).

The QoIs are active against a broad range of  plant pathogens including representatives of all three important genera of plant pathogens, the ascomycetes, basidiomycetes and oomycetes. Most of the members of the class are registered broadly on a large number of crops although a few members are registered for use on a narrower spectrum of crops and diseases. As each member of the group has its particular strengths, label recommendations for specific products should always be followed.

The first members of the QoIs were launched in 1996. Isolates of Blumeria graminis f sp. tritici (Sierotzki et al. 2000) and Plasmopara viticola (Heaney et al. 2000) resistant to QoIs were found a short time later. They were found to have a mutation in the cytochrome b gene that caused the protein to change from Gly to Ala at position 143 (G143A). For a list of plant pathogens where isolates resistant to QoIs were found see Species with QoI Resistance (Status Dec. 2012).

The three amino acid substitutions detected in the cytochrome b gene that govern resistance to Qo inhibitors in plant pathogens are:

• Change from glycine to alanine at position 143 (G143A)
• Change from phenylalanine to leucine at position 129 (F129L)
• Change from glycine to arginine at position 137 (G137R)

All G143A, G137R and F129L are based on single nucleotide polymorphisms in the cytochrome b gene; the selection process is qualitative (single step).

Based on current knowledge, resistance factors (RF= ED₅₀ [resistant strain] / ED₅₀ [sensitive or wild-type strain]) associated with G143A, G137R and F129L are different. RFs attributed to G143A are in most cases greater than 100 and usually greater than several hundreds. Isolates carrying G143A express high (complete) resistance. Isolates with F129L or G137R express moderate (partial) resistance. QoIs applied at manufacturers’ recommended rates are shown to provide effective control of diseases with the F129L or G137R mutation. In contrast, a severe loss in disease control is always seen in populations where G143A predominates and QoIs are used alone.

For more information and a list of references, please see  Mutations Associated with QoI Resistance.

In some species the amino acid substitution of the alanine for the glycine at position 143 has not been observed despite significant use of the QoIs against these species in the field. In different Puccinia species as well as Alternaria solani and Pyrenophora teres, an intron (non-coding region of DNA) was observed directly after the triplet GGT that encodes for glycine (Grasso et al. 2006). It is predicted that the nucleotide subsitution resulting in the alanine at position 143 is lethal since this substution will strongly affect the splicing process, leading to a deficient cytochrome b (Grasso et al. 2006). As a consequence, resistance to QoI fungicides based on the G143A mutation is not likely to evolve in species such as rusts (Puccinia spp., Uromyces appendiculatus, Phakopsora pachyrhizi, Hemileia vastatrix), P. teres and A. solani. The presence of such an intron has also been reported in Monilinia laxa, Monilinia fructicola (Miessner and Stammler 2010, Luo et al. 2010) and Guignardia bidwellii (Miessner et al. 2011). However, it cannot be excluded that mutations other than G143A conferring reduced sensitivity may arise in upcoming populations selected by the use of QoI fungicides. For A. solani and P. teres the mutations F129L and/or G137R have been reported (Sierotzki et al. 2007) as a mechanism for QoI tolerance. Both mutations are of minor importance, however, because they generally lead to lower resistance factors than the G143A mutation and it has been found that these two mutations have no, or only limited impact on the field efficacy of QoIs (Semar et al. 2007).

For more information and additional references, please see Impact of Intron.

Grasso V, Palermo S, Sierotzki H, Garibalid A, Gisi U. Cytochrome b gene structure and consequences for resistance to Qo inhibitor fungicides in plant pathogens. Pest Management Science 2006; 62(6):465-472.

Heaney SP, Hall AA, Davis SA, Olaya G. Resistance to fungicides in the QoI-STAR cross resistance group: current perspectives. In The BCPC Conference: Pests and disease, Volume 2. Proceedings of an international conference held at the Brighton Hilton Metropole Hotel, Brighton, UK, 13-16 November 2000. Brighton, UK: Brighton Crop Protection Council; 2000. pp. 755-762.

Luo CX, Hu M, Luo CX, Hu MJ, Jin X, Bryson PK, Schnabel G. Evidence for the unlikely development of the QoI fungicide resistance-related G143A mutation in the Cyt b gene of Monilinia fructicola.  Pest Management Science 2010; 66:1308–1315.

Miessner S., Mann W, Stammler G. Guignardia bidwellii, the causal agent of black rot on grapevine has a low risk for QoI resistance. Journal of Plant Diseases and Protection 2011; 118(2), 51-53.

Miessner S., and Stammler G. Monilinia laxa, M. fructigena and M. fructicola: Risk estimation of resistance to QoI fungicides and identification of species with cytochrome b gene sequences. J. Plant Dis. Prot. 2010; 117:162-167.

Semar M., Strobel D, Koch A, Klappach K, Stammler G.  Field efficacy of pyraclostrobin against populations of Pyrenophora teres containing the F129L mutation in the cytochrome b gene. J. Plant Dis. Prot. 2007; 114:117-119.

Sierotzki H, Wullschleger J, Gisi U. Point-mutation in cytochrome b gene conferring resistance to strobilurin fungicides in Erysiphe graminis f. sp. triticifield isolates. Pesticide Biochemistry and Physiology 2000; 68:107-112.

Sierotzki H, Frey R.  Cytochrome b gene sequence and structure of Pyrenophora teres and P.tritici-repentis and implications for QoI resistance. Pest Manag. Sci. 2007; 63:225-233.

(Reviewed January 2024; No changes)

Where the guidelines were followed, field performance of QoI containing spray programmes was good. It continues to be essential to use non-cross resistant mixture partners (e.g. SBIs, multi-sites) to ensure robust disease management. This will also help to delay the evolution of resistance, especially in regions with no resistance or where resistance is at low levels.

Therefore, the recommendations remain unchanged.

Guidelines for using QoI fungicides on cereal crops.

1. Apply QoI fungicides always in mixtures with non-cross resistant fungicides to control cereal pathogens. At the rate chosen the respective partner(s) on its/ their own has/ have to provide effective disease control. Refer to manufacturers' recommendations f or rates. 
2. The maximum number of QoI-containing sprays is 3, but only when QoI fungicides belonging to both QoI Groups (code 11 and 11A) are included in a spray program. QoI fungicides belonging to the individual Codes (11 or 11A) should not be applied more than 2 times either individually or when mixed together. 
3. Apply QoI fungicides according to manufacturer’s recommendations for the target disease (or complex) at the specific crop growth stage indicated. 
4. Apply the QoI fungicide preventively or as early as possible in the disease cycle. Do not rely only on the curative potential of QoI fungicides. 
5. Split / reduced rate programmes, using repeated applications, which provide continuous selection pressure, accelerate the development of resistant populations and therefore must not be used.

For a printer friendly version of these use recommendations see section 2.2.1 of  the latest "Minutes of the QoI Working Group Meeting" below.

(Reviewed January 2024; No changes)

Apply a maximum of 4 QoI fungicide containing sprays against any disease per vine crop, and a maximum of 33% of the total number of applications.

Powdery mildew (Uncinula necator / Erysiphe necator)

1. Apply QoI fungicides according to manufacturer's recommendations for the target disease at the specific crop growth stage indicated. Effective disease management is a critical parameter in delaying the build-up of resistant pathogen populations. 
2. Apply a maximum of 2 QoI fungicide-containing sprays targeted against powdery mildew per vine crop, preferably in mixture (co-formulations or tank mixes) with effective mixture partners from different cross-resistance groups. 
3. Apply QoI fungicides preventively. 
4. QoI fungicides used solo should be used in strict alternation with fungicides from a different cross-resistance group. 
5. Apply QoI fungicides used in mixture in a maximum of two consecutive applications in alternation with fungicides from a different cross-resistance group. In areas where resistance has been confirmed, apply QoI fungicides in strict alternation.

Downy mildew (Plasmopara viticola)

1. Apply QoI fungicides according to manufacturer's recommendations for the target disease at the specific crop growth stage indicated. Effective disease management is a critical parameter in delaying the build-up of resistant pathogen populations. 
2. Apply QoI fungicides preventively. 
3. Apply a maximum of 3 QoI fungicide containing sprays targeted against downy mildew per vine crop, only in mixture with effective partners from different cross-resistance groups. 
4. Apply QoI fungicides in single or block application in alternation with fungicides from a
   different cross-resistance group.

For a printer friendly version of these use recommendations see section 2.2.2.2 of the latest "Minutes of the QoI Working Group Meeting" below.

(Reviewed January 2024; No changes)

Scab (Venturia inaequalis, Venturia pirina)

1. Apply Apply QoI fungicides according to manufacturers' recommendations for the target disease (or complex) at the specific crop growth stage indicated and adapted to size of trees. Effective disease management is a critical parameter in delaying the build-up of resistant pathogen populations. 
2. QoI fungicides must be applied only in mixture with partners contributing to the effective control of the target pathogens. 
3. Apply QoI fungicides preventatively. Under high disease pressure the spray interval should not exceed 7-10 days. 
4. Apply a maximum of 3 QoI containing sprays per crop. A maximum of 4 QoI fungicide applications may be used where 12 or more applications are made per crop. 
5. A maximum of 2 consecutive QoI fungicide sprays is preferred. Where field performance was adversely affected apply QoI containing fungicides in mixtures in strict alternation with fungicides from a different cross-resistant group.

For a printer friendly version of these use recommendations see section 2.2.2.3 of the latest "Minutes of the QoI Working Group Meeting" below.

(Reviewed January 2024; No changes)

Late blight (Phytophthora infestans)

1. Apply QoI fungicides according to manufacturer's recommendations for the target disease (or complex) at the specific crop growth stage indicated. Effective disease control management is a critical parameter in delaying the build-up of resistant pathogen populations. 
2. Where QoI fungicide products are applied alone, do not exceed 1 spray out of 3 with a maximum of 3 sprays per crop. Do not use more than 2 consecutive applications. 
3. Where QoI fungicide products are applied in mixtures (co-formulations or tank mixes) do not exceed 50% of the total number of sprays or a maximum of 6 QoI fungicide applications whichever is the lower. Do not use more than 3 consecutive QoI fungicide containing sprays.
   
   

Early blight (Alternaria solani, Alternaria alternata)

1. Where QoI fungicide products are applied solo do not exceed 33% of the total number of sprays or a maximum of 4.
2. Where mixtures (co-formulations or tank mixes) are used, do not exceed 50% of the total number of sprays or a maximum of 6 QoI fungicide applications, whichever is the lower.
3. Where resistance has been confirmed, QoI fungicides must be applied only in mixture with partners contributing to the effective control of the target pathogens.

(Reviewed January 2024; No changes)

QoI fungicides control soybean diseases including rust, which is a major disease in Latin America and has been detected recently in the USA. 

In order to ensure sustainable use of QoIs the Working Group recommends:

1. Apply QoI fungicides according to manufacturer's recommendations for the target disease (or complex) at the specific crop growth stage indicated. Effective disease management is a critical parameter in delaying the build-up of resistant pathogen populations. 
2. Use QoIs preventatively or as early as possible in the disease cycle. 
3. Use QoIs preferably in mixtures (co-formulations or, where permitted, tank mixes) with fungicides from a different cross-resistance group. At the rate chosen, each partner on its own has to provide effective disease control. Refer to manufacturers’ recommendations for rates. In regions where target site mutations in key target soybean pathogens are present mixtures are mandatory. 
4. Limiting the number of sprays containing QoI fungicides is an important factor in delaying the build-up of resistant pathogen populations.

Good agricultural practices must be considered to reduce source of inoculum, disease pressure and resistance risk, e.g. no multiple cropping, implement and respect soybean-free periods, consider varietal tolerance, reduce the planting window, give preference to early-cycle varieties or endorse the destruction of volunteers.

(Reviewed January 2024; No changes)

Cercospora beticola

1. Apply QoI fungicides according to manufacturer’s recommendations for the target disease (or complex) at the specific crop growth stages indicated. Effective disease management is a critical parameter in delaying the build-up of resistant pathogen populations. 
2. QoI fungicides must be applied only in mixture with partners from a different cross-resistance group, contributing to the effective control of the target pathogens. 
3. Apply QoI fungicides preventatively. Under high disease pressure the spray interval should not be extended. 
4. The maximum number of QoI-containing sprays is 3, but only when QoI fungicides belonging to both QoI Groups (code 11 and 11A) are included in a spray program. QoI fungicides belonging to the individual Codes (11 or 11A) should not be applied more than 2 times either individually or when mixed together. 
5. Do not exceed 50% of the total number of sprays with QoI containing products. In low disease pressure situations where only one fungicide application is required for disease control, then a QoI – containing mixture (as defined above) may be used. In areas where ‘exactly’ three applications are expected, a maximum of one QoI 11 and a maximum of two QoI 11A may be applied so long as not more than two QoI applications are made in total.

Where QoI fungicides are used targeting other sugar beet diseases (e.g. rust, powdery mildew, Rhizoctonia, Ramularia and Stemphylium), then the potential impact of applications on the resistance management of Cercospora beticola should be considered. Where Cercospora beticola is not a disease of importance (e.g. in a certain geography) then the general guidelines for QoI fungicides apply.

(Reviewed January 2024; No changes)

1. Apply QoI fungicides according to manufacturers' recommendations for the target disease (or complex) at the specific crop growth stage indicated. Effective disease management is a critical parameter in delaying the build-up of resistant pathogen populations.
2. Apply a maximum of 3 QoI fungicide sprays per crop.
3. Use a maximum of 1 QoI fungicide spray out of every three fungicide applications.
4. Do not use consecutive applications of QoI fungicides.
5. Apply QoI fungicides in alternation with fungicides from a different cross-resistance group with satisfactory efficacy against the targeted pathogen(s).
6. Continue QoI fungicide alternation between successive crops.

(Reviewed January 2024; No changes)

1. Apply QoI fungicides according to manufacturers' recommendations for the target disease (or complex) at the specific crop growth stage indicated. Effective disease management is a critical parameter in delaying the build-up of resistant pathogen populations.
2. Use a maximum of 1 QoI fungicide spray out of every 3 fungicide applications.
3. Do not use consecutive applications of QoI fungicides.
4. Apply QoI fungicides in alternation with fungicides from a different cross-resistance group with satisfactory efficacy against the targeted pathogen(s).
5. Continue QoI fungicide alternation between successive crops.

Reviewed January 2024; No changes)

1. Apply QoI fungicides according to manufacturers recommendations for the target disease (or complex) at the specific crop growth stage indicated. Effective disease management is a critical parameter in delaying the build up of resistant pathogen populations.
2. Observe spray limitations in the spray guideline table shown below for programs utilizing 12 or fewer fungicide sprays per crop.

Spray guideline table:

Table Footnotes:
* When more than 12 fungicide applications are made, observe the following guidelines:

• When using a QoI fungicide as a solo product, the number of applications should be no more than 1/3 (33%) of the total number of fungicide applications per season.
• For QoI mixes in programs in which tank mixes or premixes of QoI with mixing partners of a different mode of action are utilized, the number of QoI containing applications should be no more than ½ (50%) of the total number of fungicide application per season.
• In programs in which applications of QoI are made with both solo products and mixtures, the number of QoI containing applications should be no more than ½ (50%) of the total number of fungicide applied per season.

** Mixtures are preferred

For a printer friendly version of these use recommendations see section 2.2.2.7, 2.2.2.8, and 2.2.2.9 of the latest "Minutes of the QoI Working Group Meeting" below.

(Reviewed January 2024; No changes)

Rice Blast (Pyricularia oryzae, Magnaporthe oryzae)

1. Apply a maximum of 2 foliar treatments per season.
2. Use QoI fungicides only in mixtures with non-cross resistant fungicides. At the chosen rate, the respective partner(s) on its/ their own has/ have to provide effective disease control. Refer to manufacturers recommendations for rates.
3. Apply QoI fungicides in programs with fungicides of different modes of action.
4. Although QoI fungicides for seed production should be avoided, the very limited amount of different modes of action available for rice blast control could justify QoI uses (in mixtures) only in areas without confirmed QoI resistance. 
5. Apply QoI fungicide based products at effective rates and intervals according to manufactures’ recommendations. 
6. To keep good field sanitation, avoid transplanting diseased seedlings, remove or destroy primary infection source e.g. left-over seedlings, infested straw and chaff.
   
   

Seedling box, paddy granule or seed treatment applications in Rice
QoIs are and will be used as seedling box, paddy granule or seed treatment products.

It is FRAC’s objective to protect this fungicide group and integrate all uses into technical recommendations. These minutes contain a recommendation on seed treatments, including those which have efficacy on foliar pathogens.

These recommendations will be reviewed regularly and supported by monitoring.

1. When a QoI fungicide is used as seedling box, paddy granule or seed treatment on rice, there should be no implications regarding QoI FRAC guidelines on the use of foliar QoI fungicides on the same crop as long as the QoI seed treatment is directed by rate and efficacy against seed and soil borne diseases or ‘low risk’ foliar pathogens. (Link to FRAC pathogen risk classes)
2. QoIs used as seedling box, paddy granule or seed treatment in rice providing foliar efficacy against pathogens with moderate/ high resistance risk count against the total number of QoI applications.
3. If QoI seedling box, paddy granule or seed treatment with foliar efficacy has been used, first foliar application have to be made with a different mode of action in the vegetative phase before subsequent QoI-based foliar sprays in the reproductive phase.
4. Please refer to the recommendations of Japan-FRAC.

For a printer friendly version of these use recommendations see section 2.2.2.10 of the latest "Minutes of the QoI Working Group Meeting" below.

Please refer to the recommendations of the banana FRAC working group: The conclusions and guidelines of the meetings of the FRAC Banana Working Group are available on the FRAC Website (https://www.frac.info/frac-teams/working-groups/banana-group/recommendations-for-bananas).

Crops and pathogens not covered above with a specific recommendation, follow the general guidelines.