Quinone outside inhibitor (QoI) [Group 11] resistance management strategy

Black spot on apple leaves.
Black spot Venturia inaequalis on apple leaves

Updated 2023, R. Beresford and M. Christie

Disclaimer:

The fungicide and bactericide resistance information in the mode of action group table, the mode of action-based strategies and the crop-based strategies is intended to help manage the effects of pesticide resistance on plant disease control by agrochemicals in New Zealand. The New Zealand Committee on Pesticide Resistance (NZCPR) is a subcommittee of the New Zealand Plant Protection Society (NZPPS). The following parties: NZCPR, NZPPS, any people named in the strategies and any organisation the people may be affiliated with, do not guarantee that the resistance information is complete, consistent, accurate or up-to-date, or that resistance will not develop, or that the degree of resistance will decrease, as a result of the resistance information being used, and the parties accept no liability for loss or damage arising from the use of the resistance information contained in these strategies.

Also see the separate crop-based strategies for use of QoIs against Venturia inaequalis (black spot; scab) in apples, here, and against Monilinia spp. in Summerfruit (here).

QoI Product Perspective

Quinone outside inhibitor (QoI) fungicides are synthetic derivatives of naturally occurring strobilurin compounds and, in the absence of resistance, are active against a broad spectrum of fungi and oomycetes (Table 1). They have a site-specific mode of action that inhibits fungal respiration at the Quinone "outside" (Qo) binding site of the cytochrome bc1 complex. The site-specific mode of action means they are at risk from the development of resistance in the target plant pathogens. QoIs are not cross-resistant with other fungicide groups, but there is strong cross-resistance among all the active ingredients within the QoI group. QoIs were first introduced into New Zealand in the late 1990s. The active ingredients registered in New Zealand are shown in Table 2. The range of pathogens against which the various QoI compounds are effective differs with the compound.

Table 1: Pathogens and crops targeted by QoI fungicides in New Zealand.
PathogenDiseaseCrops
Horticultural crops
Alternaria solani Early blight Potatoes, tomatoes
Botrytis cinerea Grey mould Grapes
Erysiphe cichoracearum, Sphaerotheca fuliginea Powdery mildew Cucurbits
Peronospora destructor Downy mildew Onions
Phytophthora infestans Late blight Potatoes, tomatoes
Plasmopara viticola Downy mildew Grapes
Podosphaera leucotricha Powdery mildew Apples
Uncinula necator Powdery mildew Grapes
Venturia inaequalis, V. pirina Black spot Apples, pears
Monilinia fructicola Brown rot Stonefruit
Cereal crops
Blumeria graminis Powdery mildew Cereals
Cochliobolus sativus Spot blotch Barley
Didymella phleina Didymella leaf scorch Barley, wheat
Puccinia spp. Rusts Cereals, ryegrass
Pyrenophora teres Net blotch Barley
Species of Alternaria, Cladosporium, Stemphylium and Fusarium Head disease complex Cereals
Ramularia collo-cygni Ramularia leaf and awn spot Barley
Rhynchosporium secalis Scald Barley
Septoria nodorum, S. tritici Glume blotch, speckled leaf blotch Wheat
Table 2: QoI fungicides marketed in New Zealand.
Common nameTrade names
azoxystrobin Agpro Azoystrobin 250SC, Amistar®, Amistar® Opti, Sinon A-star 250 SC, Avior, Azoxystar®, Aztrostar, Custodia®, Atlantis® Flo, Inspire®, Mirador®, Orbit®, Radial®, Roxy®, Tazer®, Yizostar
fenamidone Reason
kresoxim-methyl Ardent®, Vista Flo,
in Colliss® with boscalid
picoxystrobin Comet®, Convoy™, Energy, Essence, Merivan®, Pyrax®, Pyroin, Wynca Pyraclo in Pristine® with boscalid
pyraclostrobin

Comet

in Pristine with boscalid
trifloxystrobin Polestar, Flint®, Twist, Protiva®, Mondo®, Tstar, Escolta®, Delaro®, TriPlus™, Luna Sensation®, Beetrizole®, Stribor

Current status of QoI resistance

QoI fungicides are at high risk from resistance in multiple target pathogens. When resistance occurs, it is of the disruptive selection type producing a high degree of resistance with loss of disease control and the resistance appears to be stable over time. Instances of QoI resistance that have been confirmed in New Zealand include the following (and there are others):

Overseas, several instances of reduced sensitivity or field resistance have been recorded:

For these diseases FRAC considers it mandatory to use QoI fungicides in mixture with a fungicide from a different cross-resistance group.

Resistance prevention strategy

For pathogens/crops where it is known resistance has not developed, apply a maximum of three QoI fungicide-containing sprays per season or per 12 month period, unless otherwise indicated for specific crops (Table 3). Whenever practical, use in mixture with effective partners from different cross-resistance groups. Apply QoI fungicides according to manufacturers' recommendations for the target disease and crop. Effective disease management is critical in delaying the build-up of resistant pathogen populations. Different QoI active ingredients applied in one season count towards the maximum numbers of applications recommended for a given crop. Use application rates recommended by the manufacturer in order to ensure good disease control and resistance management. The FRAC QoI working group is concerned with the trend towards the application of decreased dose rates. 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.

Table 3: QoI use guidelines for specific crops.
CropDiseaseRecommendations
Grapes Downy mildew (Plasmopara viticola)

A maximum of three QoI-containing applications per vine crop, in alternation with fungicides from a different group. 

Note: grapevine powdery mildew (Erysiphe necator) has developed widespread QoI resistance in New Zealand and its control using QoI fungicides should not be attempted.
Apples Powdery mildew

Apple powdery mildew (Podosphaera leuchotrica) is believed to still be sensitive to QoI fungicides in New Zealand. Use a maximum of three QoI-containing applications per season in mixture with an effective dose of a fungicide from a different cross-resistance group.
Apply a maximum of two consecutive QoI-containing applications in strict alternation with an effective dose of a non-QoI fungicide.
Apply QoI fungicides preventatively.
Follow individual product label recommendations regarding shorter application intervals during periods of high disease risk.

Note: Apple black spot (Venturia inaequalis) has developed widespread QoI resistance in New Zealand and its control using QoI fungicides should not attempted.
Cereals Powdery mildew, speckled leaf blotch, glume blotch, rusts, net blotch, scald, spot blotch, Ramularia leaf and awn spot, Didymella leaf scorch Apply a maximum of two QoI fungicide-containing sprays per cereal crop. Limiting the number of sprays is an important factor in delaying the build-up of resistant pathogen populations.
To control cereal pathogens, always apply QoI fungicides in mixture with an effective dose of a non-QoI fungicide that on its own would provide effective disease control. Refer to manufacturers’ recommendations for application rates.
Repeated applications using "split" or reduced application rates must not be used, as they provide continuous selection for resistance.
Other fruit and vegetable crop pathogens where QoI resistance is known not to be present Apply a maximum of three QoI fungicide-containing sprays per crop. A maximum of four QoI fungicide applications may be used where 12 or more applications are made per crop.
Apply in mixture with an effective dose of a fungicide from a different group.
Use a maximum of two consecutive QoI fungicide applications.

Implementation recommendations

The known high resistance risk to QoIs in New Zealand dictates that QoI resistance management guidelines must be strictly adhered to. Product labels for products that contain QoIs should include an appropriate statement about resistance management.

Acknowledgements

This strategy includes information from The Fungicide Resistance Action Committee (FRAC) about mode of action groups, the occurrence of resistance worldwide and resistance management recommendations.