• Introduction
• Herbicides
• Insecticides & miticides
• Fungicides & bactericides

• 
• Fungicide & bactericide resistance
• Management principles
• Anilino-
  pyrimidines
• Benzimidazoles
• Carboxylic acid amides
• Demethylation inhibitors
• Dicarboximides
• Dodine
• Morpholines
• Phenylamides
• Qo inhibitors
• Streptomycin
• NZ Plant Protection Society

Qo inhibitor (QoI) management strategy

R.M. Beresford
HortResearch, Private Bag 92169, Auckland, New Zealand

(Revised August 2005)

Introduction

These guidelines are designed to manage or prevent the problem of resistance to QoI (also known as strobilurin or STAR) fungicides in New Zealand. They have been developed from previously published information (Beresford et al. 1999) in consultation with the New Zealand Association for Animal Health and Crop Protection (AGCARM) and are based on recommendations from the Fungicide Resistance Action Committee (FRAC) in Europe.

QoI Product Perspective

QoI fungicides are synthetic derivatives of naturally occurring strobilurin compounds and are active against a broad spectrum of fungi (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 cross-resistance among all the active ingredients within the QoI group. QoIs were first introduced into New Zealand in the late 1990s. Of the active ingredients so far developed (azoxystrobin, dimoxystrobin, famoxadone, fenamidone, fluoxastrobin, kresoxim-methyl, metominostrobin, orysastrobin, picoxystrobin, pyraclostrobin and trifloxystrobin), five are commercially available in New Zealand (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.

Pathogen	Disease	Crops
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
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 name	Trade name
azoxystrobin	Amistar
fenamidone	Sereno
fluoxastrobin	in Fandango with prothioconazole
kresoxim-methyl	Stroby in Collis with boscalid in Allegro with epoxiconazole
picoxystrobin	Acanto
pyraclostrobin	Comet
trifloxystrobin	Flint, Twist

Current status of QoI resistance

No instances of QoI resistance have yet been confirmed in New Zealand. Overseas, several instances of reduced sensitivity or field resistance have been recorded:

• in wheat and barley, powdery mildew (Blumeria graminis) and speckled leaf blotch (Septoria tritici) in UK and Northern Europe
• in grapes, downy mildew (Plasmopara viticola) in Europe and Brazil and powdery mildew (Erysiphe necator syn. Uncinula necator) in USA
• in banana, black Sigatoka disease (Mycosphaerella fijiensis) in Costa Rica
• in cucurbits, powdery mildew (Sphaerotheca fuliginea, Podosphaera fusca) in UK, Italy, France, Spain, Korea, Japan, Taiwan and The Netherlands, downy mildew (Pseudoperonospora cubensis) in Taiwan and Japan and gummy stem blight (Didymella bryonia) in USA
• in chrysanthemum, white rust (Puccinia horiana) in Korea and UK
• in potato, early blight (Alternaria solani) in USA

Overseas, it is considered that there is a high risk of resistance development in the apple black spot pathogen (Venturia inaequalis) and in the grape downy mildew pathogen (Plasmopara viticola). 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

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.

Crop	Disease	Recommendations
Grapes	Powdery mildew, downy mildew	A maximum of three QoI-containing applications per vine crop, in single or block application in alternation with fungicides from a different group. Use early in the season before powdery mildew is well established.
Apples	Black spot, powdery mildew	Apply QoI fungicides in mixture with an effective dose of a fungicide from a different cross-resistance group. Use a maximum of three QoI-containing applications per season. Where more than 12 fungicide applications are made in total per season, apply a maximum of four QoI fungicides. Apply a maximum of two consecutive QoI-containing applications. Where there may be a loss of field performance, apply QoI-containing fungicides in strict alternation with an effective non-QoI fungicide. Apply QoI fungicides preventatively. Follow individual product label recommendations regarding shorter application intervals during periods of high disease risk.
Cereals	Powdery mildew, speckled leaf blotch, glume blotch, rusts	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. Apply QoI fungicides in mixtures to control cereal pathogens. At the rate chosen each mixing partner on its own has to provide effective disease control. Refer to manufacturers recommendations for rates. Repeated applications using "split" or reduced application rates must not be used, as they provide continuous selection for resistance.
Other fruit and vegetable crops		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. A maximum of two consecutive QoI fungicide sprays is preferred.

Implementation recommendations

The rapid increase in the number of label claims for QoI use in New Zealand, together with the known high resistance risk, 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 resistance management strategy has been compiled with assistance from Jack Richardson (AGCARM), George Follas (Syngenta Crop Protection), Grant Hagerty (BASF New Zealand), Max Moore (Bayer CropScience), Ken Jeffery (Fruitfed Supplies Ltd) and Nick Pyke (Foundation for Arable Research).

Reference

© 2007 New Zealand Plant Protection Society (Inc.)