Summaries and recommendations from the 2004 meeting of the Fungicide Resistance Action Committee (FRAC)

Sterol Biosynthesis Inhibitor

(SBI) Working Group

Key Points from meeting
ANNUAL MEETING 2004
INTRODUCTION
DEFINITIONS - SBI-Fungicides
CEREAL DISEASES
GENERAL RECOMMENDATIONS for Cereals (SBI’s)
Quinoxyfen
Fenhexamid
GENERAL RECOMMENDATIONS for the use of SBI- Fungicides

Generally in 2004 a stable situation was found with DMI’s and morpholines.
The guidelines for adherence to recommended use rates were emphasised for cereals.

Wheat

Powdery mildew: stable situation (DMI and morpholine)
Septoria tritici: DMI’s field performance was generally good but in some cases affected by late curative application and too low dose rates. (DMI). A slight increase in the frequency of less sensitive isolates has been observed over the last 3 years.
Yellow and brown rust: field performance of DMI’s remains good.

Barley

Rhynchosporium: Generally stable situation.
Net blotch: DMI performance unchanged.
Powdery mildew: stable situation (DMI and morpholine)

Vines

Powdery mildew: performance unchanged (DMI and morpholine).

Apples

Scab: DMI performance unchanged.
Powdery mildew: DMI performance unchanged.

Fenhexamid (hydroxyanilide) – new SBI class

No change in sensitivity and performance against Botrytis since introduction in 1998.

Quinoxyfen (non-SBI phenoxyquinoline)

Wheat

Resistance to quinoxyfen is established in the north of Germany but has stabilised from 2003 to 2004.

Grapes

No change in sensitivity or performance since introduction in 1999.

Class I: DMI-Fungicides

SBI-fungicides that inhibit the C14 demethylation step within fungal sterol biosynthesis are now commonly characterised as DeMethylation-Inhibitors (Abbreviation: DMI’s).
Chemically, DMI’s belong to different classes. Beside triazoles, numerous imidazoles, pyridines and pyrimidine all have been shown to act as demethylation inhibitors.
Typically, DMI's have a broad spectrum of activity against a range of economically important pathogens on arable crops, top fruit, vines, plantation crops, etc.

Class II: "Morpholine"-Fungicides

Like the DMI’s the “Morpholine”-fungicides also belong to different chemical classes. The first representatives of this group were chemically morpholines. Although representatives of two other chemical groups (piperidines and spiroketalamines) have entered the market, the group designation “Morpholines” is now commonly used for all three chemical classes. “Morpholines” inhibit (to a variable degree) two target sites within the sterol biosynthetic pathway, the Δ⁸ → Δ⁷ isomerase and the Δ¹⁴ reductase.
" Morpholines" have a narrower spectrum of activity than the DMI’s. They can be used alone but are often used in mixtures with DMI's to control cereal powdery mildews and rusts.

Class III: Hydroxyanilide -Fungicides

Currently this class is represented by fenhexamid. Hydroxyanilides inhibit the C3-keto-reductase step in ergosterol biosynthesis. Hydroxyanilides have a narrower spectrum of activity than the DMI’s and morpholines – fenhexamid is a specific botryticide, which does not show cross-resistance to other classes of anti-Botrytis fungicides.

Resistance to fungicides

Resistance to fungicides is a normal phenomenon embodied in the natural process of the evolution of biological systems. By close co-operation within the agrochemical industry and collaboration with researchers, advisors and with growers we can ensure that fungicides are used optimally and continue to offer the benefits they currently confer.

Resistance to SBI fungicides

Resistance to SBI fungicides has been well characterised during the last 20 years. Problems with SBI performance typically became obvious only after several years of intensive use with efficacy degrading stepwise. Following reduced selection pressure, a recovery in sensitivity is often observed.
The mechanism of resistance is mostly controlled by the accumulation of several independent mutations and is generally referred to as “continuous selection”, “quantitative resistance” or “shifting”.

Cross Resistance among SBI-fungicides

Whilst there is positive cross-resistance amongst the DMI's and amongst the "morpholines", there is no cross-resistance between the DMI's and the "morpholines”.

The recommendations for the use of DMI and "morpholine" fungicides in mixture or alternation programmes with different mode of action fungicides remain unchanged.

	Repeated application of DMI or “morpholine“ fungicides alone should not be used on the same crop in one season against a high-risk pathogen (e.g. cereal powdery mildews, barley net blotch or barley scald) in areas of high disease pressure for that particular pathogen.
	Reduced rates of DMIs have been shown to accelerate the shift to less sensitive populations. It is critical to use effective rates of DMIs in order to ensure robust disease control (refer to QoI recommendations on FRAC web site). DMIs must provide effective disease control and be used at Manufacturers recommended rates.
	When used in mixture recommended effective rates of the SBI should 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 in situations of high disease pressure it is of importance to adhere to dosages and spray timings as recommended by manufacturers. Highly curative late applications should be avoided. Mixing with a non-DMI fungicide at effective dose rates may contribute to a higher level of disease control.
	The “morpholine” fungicides are effective non-cross-resistant partner fungicides for DMI’s on cereals for the control of powdery mildew.

This compound is not an SBI but is being reviewed under the SBI-FRAC umbrella for convenience

	For effective powdery mildew control quinoxyfen is recommended to be used in alternation or in combination with fungicides of different modes of action.
	A maximum number of 2 applications per season are recommended. The practical use rates of quinoxyfen should be kept between 50 and 100 gai/ha per application.
	Quinoxyfen should only be applied in the spring - autumn applications are not recommended.

NON-CEREAL DISEASES

Recommendations:

DMI´s should only be used as preventatives and not in a curative manner. “Morpholines” should preferably be used as preventatives and not in a curative manner.

The existing strategy for effective disease control and resistance management continues to be successful and the use recommendation is a maximum of 4 applications per season, before symptoms occur. The strategy includes the use of mixtures or alternation with non-cross resistant fungicides.

To ensure that SBI's can remain as the effective basis for Uncinula control in vines, the use of the full-recommended rate (either alone or in mixture), recommended timing, application volume and accurate treatment of each row should be adhered to.

Apple Scab (Venturia inaequalis)

The performance of DMI’s was good on this disease in 2004 when compounds were used according to the manufacturers’ and FRAC recommendations. Sensitivity data indicated that no new sensitivity classes have appeared since 1993 although the most sensitive class have disappeared as shown in 2003 and 2004 compared to 1993.

Recommendations:

DMI fungicides, which are labelled for scab control, are not recommended for season long use and a maximum of 4 DMI sprays either alone or in mixture are recommended.

Where repeated fungicide applications are required, DMI's should be used in mixtures or (block) alternations with a non-cross resistant fungicide. Application of recommended label rates is important.

Preventative applications should always be the first choice with DMI’s. Curative applications are only recommended when accurate disease warning systems are available.

Apple Powdery Mildew (Podosphaera leucotricha)

No complaints were received on the performance of DMI’s when compounds were used according to the manufacturers’ recommendation and FRAC recommendations.
For recommendations see General Recommendations.

Banana Sigatoka (Mycosphaerella fijiensis)

The conclusions and guidelines of the Feb. 2004 meeting of the FRAC Banana Working Group are available on the FRAC Website.

Considered a SBI with activity on Botrytis cinerea, which is a high-risk disease. New biochemical mode of action and no x-resistance with other botryticides. Targets 4,4-dimethylfecosterol and 4,alpha-dimethylfecosterol in Sterol biosynthesis pathway (C4 demethylation) Regarded as an inhibitor of C3-ketoreductase.

In-vitro resistance can be found for B.cinerea. Studies in a long-term trial 1992 – 1996 showed a small percentage of isolates of >0.2 ppm (metabolising isolates) were present, but these had been detected for several years before launch in 1998. In practice no accumulation of isolates can be detected after several years of fenhexamid treatment.

2003 monitoring studies with populations from France, Australia and Chile have shown no sensitivity shift. No complaints in practice in 2004.

Recommendations for use of Fenhexamid:

Use fenhexamid only protectively.

Straight product:

	Spray schedules with a maximum of 3 treatments per season: max. 1 application with fenhexamid
	Spray schedules with 4-5 treatments/season: max. 2 applications with fenhexamid
	Spray schedules with 6 and more treatments: at the maximum one third of all Botryticide-applications

Mixtures:

Both partners - if applied alone at the dose used in the mixture - must have sufficient activity against Botrytis. Not more than 50% of all Botryticide-treatments should be made with fenhexamid-containing mixtures.

The summaries and recommendations included in this report are based upon data generated by members of the FRAC-SBI Working Group and upon the work of non-industry collaborators. The working group concentrates its resources on the major crop/pathogen targets from the point of view of resistance risk. Inevitably many, still important, pathogens are omitted. To help in making recommendations for crops and pathogens not directly covered above, the following general recommendations can be made:

	Repeated application of SBI fungicides alone should not be used on the same crop in one season against a high-risk pathogen in areas of high disease pressure for that particular pathogen.
	For crop/pathogen situations where repeated spray applications (e.g. orchard crops/powdery mildew) are made during the season, alternation (block sprays or in sequence) or mixtures with an effective non cross-resistant fungicide are recommended.
	Where alternation or the use of mixtures is not feasible because of lack of effective or compatible non cross-resistant partner fungicides, then input of SBI's should be reserved for critical parts of the season or crop growth stage.
	If DMI's or "morpholine" performance should decline and sensitivity testing has confirmed the presence of less sensitive forms, SBI's should only be used in mixture or alternation with effective non cross-resistant partner fungicides.
	The introduction of the new classes of chemistry offers new opportunities for more effective resistance management. The use of different mode of actions should be maximised for the most effective resistance management strategies.
	Users must adhere to the manufacturers’ recommendations. In many cases, reports of “resistance" have, on investigation, been attributed to cutting recommended rates of use, or to poor or miss-timed application.
	Fungicide input is only one aspect of crop management. Fungicide use does not replace the need for resistant crop varieties, good agronomic practice, plant hygiene/sanitation, etc.

J.-M. Gouot
Chairman

Bayer CropScience SA
La Dargoire Research Center
14/20 Rue Pierre Baizet
69263 Lyon Cedex 09,
France
Tel: +33 47 28 52 391
Fax: +33 47 28 52 871
Email: J.-M. Gouot

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