Fungicide resistance management strategy for wheat septoria tritici blotch (Zymoseptoria tritici) in New Zealand

M. Christie 2022; updated 2023, R. Beresford

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.

Introduction

Septoria tritici blotch (STB), caused by the pathogen Zymoseptoria tritici is the major disease affecting commercial wheat crops in New Zealand (Foundation for Arable Research trial data). Symptoms of STB include brown necrotic lesions that contain small black pycnidia or fruiting bodies.

Development of STB in crops is determined by the amount of inoculum present, weather conditions and cultivar susceptibility. Conditions favouring infection are leaf wetness and high relative humidity (>85% for 20 hours or more) between the start of stem extension (GS 30) and the end of ear emergence (GS 59), during October and November.

Integrating cultural management methods plays a key role in minimising disease development within a crop and the risk of fungicide resistance. These methods can include.

Removal or burning of stubble
Crop rotation (avoiding wheat on wheat)
Adjust to later sowing date
Use of genetically resistant wheat varieties

Fungicides should be used as protectant treatments when conditions are conducive to disease development but prior to the appearance of disease.

Fungicide groups at risk from resistance in Z. tritici

Fungicide Resistance Action Committee (FRAC) mode of action (MOA) groups that are at risk from resistance and require resistance management for use in STB control are as follows:

Group 1 Methyl benzimidazole carbamate (MBC) High risk
Group 3 Demethylation inhibitor (DMI) Medium to high risk
Group 7 Succinate dehydrogenase inhibitor (SDHI) Medium to high risk

Group 21 Quinone inside inhibitor (QiI) Medium to high risk

There is no cross resistance to QoI and QiI fungicides. Table 1 lists the active ingredients available in these groups in New Zealand. The Group M4 phthalimide fungicide, folpet, is not at risk from resistance development.

**Table 1:** Fungicides registered for septoria tritici blotch control in NZ by mode of action group.
FRAC mode of action group		Active ingredient	Product trade names
1	MBC	Thiophanate-methyl
3	DMI - imidazole	prochloraz
3	DMI - triazole	mefentrifluconazole Epoxiconazole Propiconazole Prothioconazole Tebuconazole Triadimenol	Revylution Accuro, Fortify, Opus, Stellar Pro-P™ Joust, Pilot, Procyon, Proline, Prothago, Thiazole, Vitalis Compass, Folicur, Hornet, Rebuke Vandia, Citadel
3 + 3	DMI + DMI	Epoxiconazole + prochloraz Prothioconazole + tebuconazole	Bolide Kestrel, Prosaro
3 + 7	DMI + SDHI	Epoxiconazole + Fluxapyroxad Prothioconazole + bixafen Prothioconazole + isoflucypram Mefentrifluconazole + fluxapyroxad	Adexar Aviator XPRO Caley IBLON Revystar
3 + 11	DMI + QoI	Epiconazole + azoxystrobin Prothioconazole + trifloxystrobin	Avior Gold, Delaro
7	SDHI	Benzovindiflupyr Fluxapyroxad Isopyrazam Isoflucypram	Elatus Plus Imtrex Seguris Flexi Vimey Iblon
21	QiI	fenpicoxamid	Questar
M4	Phthalimides	Folpet	Phoenix

Resistance management recommendations by MOA group

MBC fungicides

Apply a maximum of 2 MBC-containing sprays per wheat crop.

DMI fungicides

Apply a maximum of 3 DMI-containing sprays per wheat crop.
Repeated application of DMI or amine fungicides alone should not be used on the same crop in one season against risky pathogens (e.g. cereal powdery mildews, barley net blotch, scald) in areas of high disease pressure for that particular pathogen.
Reduced rates of DMIs can accelerate the shift to resistant pathogen populations. It is critical to use effective rates of DMIs in order to ensure robust disease control and effective resistance management. DMIs must provide effective disease control and be used at manufacturers' recommended rates.
When used in mixture, recommended effective rates of the DMI must be maintained. Split and reduced rate programmes, using multiple repeated applications at dose rates below manufacturer’s recommendations, provide continuous selection pressure and accelerate the development of resistant populations, and therefore must not be used.
To ensure good performance and particularly resistance management in situations of even low disease pressure, it is essential to adhere to dosages and spray timings as recommended by manufacturers. Curative applications should be avoided. Application timing has to be appropriate to all mix partners’ characteristics. Mixing with a non-cross resistant fungicide at effective dose rates contributes to a more effective disease control and resistance management.

SDHI fungicides

Apply a maximum of 2 SDHI containing sprays per wheat crop.
When applying resistance management strategies for SDHI fungicides expect there to be cross resistance among all members of the SDHI group.
Apply SDHI-containing products at effective rates that will provide disease control and intervals according to manufacturers’ recommendations.
Always apply SDHI fungicides in mixture with a fungicide from a different mode of action group that provides effective control of the target disease when used alone. Refer to manufacturers' recommendations for application rates.
SDHIs used as a seed treatment in cereals providing foliar efficacy count towards the total number of SDHI applications. (i.e. seed treatment counts as one application for a season)
Apply the SDHI fungicide preventively or as early as possible in the disease cycle. Do not rely only on the curative potential of SDHI fungicides.
Reduced application rate programs including multiple applications must not be used. Refer to manufacturers’ recommendations for rates.

QiI fungicides

Apply a maximum of 2 QiI-containing sprays per wheat crop.
Always apply QiI fungicides in mixture with a fungicide from a different mode of action group that provides effective control of the target disease when used alone. Refer to manufacturers' recommendations for application rates.
Apply QiI fungicides according to manufacturer’s recommendations for the target disease (or complex) at the specific crop growth stage indicated.
Apply the QiI fungicide preventively or as early as possible in the disease cycle. Do not rely only on the curative potential of QiI fungicides.
Split/reduced rate programmes using repeated applications accelerate the development of resistant populations and therefore must not be used.

Acknowledgements

FAR Cropping Strategies – Cereal Disease Management 2022
FRAC – (Fungicide Resistance Action Committee) Cereal guidelines
Novachem Agrichemical Manual