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| Key
Points from meeting |
Generally in 2003 a stable situation
was found with DMI’s and morpholines.
The guidelines for adherence to recommended use rates
were emphasied for cereals.
Wheat
Powdery mildew: stable situation (DMI and morpholine)
Septoria tritici: good field performance and generally
stable situation (DMI) but with a slight increase
in the frequency of less sensitive isolates over
the last 2 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.
Sugar Beet
Cercospora: Performance issues were reported in Italy
in 2001, a monitoring programme has been established.
Bananas
Black Sigatoka: A banana FRAC meeting is planned for
February 2004 to review recommnendations.
Fenhexamid (hydroxyanilide) – new SBI
class
No change in sensitivity and performance against Botrytis
since introduction in 1998.
Quinoxyfen (non-SBI phenoxyquinoline)
Wheat
Resistant isolates are common in the north of Germany
and present in low frequencies elsewhere – this
was stable compared with 2002.
Grapes
No change in sensitivity or performance since introduction
in 1999.
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| 2003
Meeting |
FUNGICIDE
RESISTANCE ACTION COMMITTEE
STEROL BIOSYNTHESIS INHIBITOR (SBI) WORKING GROUP
Hosting company: Bayer CropScience
Venue of the meeting: Frankfurt
Airport Business Centre, Germany
Date: 23rd October 2003
Working Group participants present
at the meeting:
| J.-M.
Gouot (Chairman) |
Bayer CropScience,
Lyon, France |
| Dr. C.
Longhurst (Secretary) |
DowAgroSciences, European Research
and Development, Letcombe, UK |
| F. Kerz-Moehlendick |
Bayer CropScience, Monheim, Germany |
| A. Mehl |
Bayer CropScience, Monheim, Germany |
| Dr. I.Gasnier |
DuPont de Nemours (France) SA,
Nambsheim, France |
| Dr. K.
Stoermer |
BASF AG, Crop Protection Division,
Limburgerhof, Germany |
| Dr. O.
Puppin |
Isagro Ricerca, Milano, Italy |
| H. Sierotzki |
Syngenta, Basel, Switzerland |
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| INTRODUCTION |
The FRAC-SBI (formerly DMI) working group
was set up in 1982. The group meets annually to review
monitoring data and to agree recommendations for the
use of SBI fungicides.
The 2003 meeting (hosted by Bayer CropScience) reviewed
the most recent monitoring work undertaken directly by
Agrochemical Companies or sponsored by them with academic
institutions. Based on a review of these data, statements
have been prepared which summarise the most up-to-date
knowledge available regarding resistance to SBI fungicides. |
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| DEFINITIONS
- SBI-Fungicides |
There are two major classes of fungicides
that comprise the Sterol Biosynthesis Inhibitor's (abbreviated
SBI's): the DMI-fungicides and the so-called “Morpholine”-fungicides.
Both classes inhibit targets within fungal sterol biosynthesis
but differ in regard to the precise target sites they
inhibit.
The SBI based fungicides represent an important class
of agricultural fungicides. They make a major contribution
to world agricultural production via their broad spectrum
of disease control and excellent field performance.
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 biosythesis.
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”.
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| CEREAL
DISEASES |
BARLEY DISEASES |
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Barley Powdery Mildew (Blumeria graminis f.sp. hordei
/ Erysiphe graminis f.sp. hordei)
In 2003 disease pressure was generally low.
“
Morpholines”
Morpholine products performed well when applied
according to label recommendations and performance
was excellent in all regions with no farmer complaints.
Sensitivity was stable and within historical variation.
Scald (Rhynchosporium secalis)
Low disease infection levels in 2003 except for
Ireland with high pressure.
Generally stable situation. No reports of poor
field efficacy. Sensitivity monitoring in 2002
has not been able to confirm reports about reduced
DMI performance in Scotland.
Net Blotch (Pyrenophora teres /Drechslera teres)
Disease incidence was low in 2003. Field disease
control was good with no problems reported. No
sensitivity data were presented. |
WHEAT DISEASES |
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Wheat powdery mildew
(Blumeria graminis f.sp. tritici / Erysiphe graminis
f.sp. tritici)
Disease pressure was moderate across Europe
DMIs:- Sensitivity data was presented for tebuconazole,
confirming that the situation was generally stable
remaining in the range of variability seen over
the past 10 years. No complaints from field use.
The performance of DMI based products was as
expected.
“Morpholines” : The sensitivity pattern
has remained stable in all monitored countries
over several years. Field performance of morpholine
based products was good with no complaints.
Quinoxyfen : This compound is not an SBI but is
being reviewed under the SBI-FRAC umbrella for
convenience.
Resistant isolates are common in the north of Germany
and present in low frequencies elsewhere. Length
of mildew control reduced in field situations.
Wheat Leaf Spot (Mycosphaerella graminicola /
Septoria tritici)
Disease pressure was low – high (e.g. Ireland)
and onset of disease was late. Good field performance
was observed . There was a generally stable sensitivity
situation (DMI) but with a further slight increase
in the frequency of less sensitive isolates (first
observed in 2002) where data is available. This
is believed to be linked to a trend towards the
use of lower dosages of DMIs (see Recommendations
for Use of DMIs in 1.2 and recommendations for
QoI use in cereals on the FRAC website). Effective
DMI’s continued to provide good disease control
in practice.
Wheat Glume Blotch (Stagonospora nodorum = Septoria
nodorum)
Disease pressure was low. Good control with DMIs
was obtained. No sensitivity data were presented.
Wheat Eyespot (Tapesia spp. / Pseudocercosporella
herpotrichoides)
No data was presented.
Rusts (Puccinia recondita and P. striiformis)
Disease pressure was moderate in 2003. Performance
of DMI’s on both brown and yellow rust has
been maintained. No significant changes in sensitivity
of Puccinia recondita were recorded over the last
3 years. |
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| Quinoxyfen
- |
| This compound is not an SBI but is being
reviewed under the SBI-FRAC umbrella for convenience
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For effective powdery mildew control
quinoxyfen is recommended to be used in alteration
or in combination with fungicides of different
modes of action. |
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A maximum number of 2 applications per season
is recommended. The practical use rates of quinoxyfen
should be kept between 50 and 100 gai/ha per application. |
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Quinoxyfen should only be applied in the spring
- autumn applications are not recommended. |
NON-CEREAL DISEASES
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Grape Powdery Mildew (Uncinula necator)
Disease pressure was low - moderate in 2003
. Performance of DMIs, “morpholines” and
quinoxyfen was good. No efficacy issues reported
in 2003.
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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 2003 when compounds were used according to the manufacturers’ and
FRAC recommendations. Sensitivity data indicated that
no new sensitivity classes had appeared since 1993
although the most sensitive class had disappeared as
shown in 2003 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.
Sugar Beet Leaf Spot (Cercospora beticola)
Disease pressure was moderate in 2003. Following alerts
two years ago in Italy a field programme to assess
the situation was started in 2003 – no efficacy
issues were observed in the trials associated with
this programme. No complaints from farmer use situations
were reported.
The general recommendations for resistance management
of SBI’s should be followed.
Banana Sigatoka (Mycosphaerella fijiensis)
The recommendations as outlined in the summaries of
the Banana FRAC-SBI Working Group meeting of February
2000, remain unchanged regarding DMI’s and “morpholines”.
The use of these FRAC guidelines should be encouraged
in all banana-growing areas. (See Section 4.)
All fungicides belonging to the DMI’s have to
be considered as one product group amongst which general
cross-resistance exists. Accordingly, alternation or
mixtures of DMI’s are of no value for resistance
management and must not be recommended for the purpose
of resistance management.
The recommendations of the Banana FRAC-Working Group
meeting of February 2000 are still valid. The part
relevant for SBI fungicides is given in part 4.0.
There will be a Banana FRAC meeting in February 2004
when banana recommendations will be reviewed.
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| Fenhexamid
(hydroxyanilides) |
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.
No field resistant isolates were detected in Australian
and Chilean populations; European monitoring studies
are still in progress. No complaints in practice in
2003.
Recommendations for use of Fenhexamid:
Use fenhexamid only protectively.
Straight product:
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Spray schedules with a maximum of
3 treatments per season:
max. 1 application with fenhexamid |
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Spray schedules with 4-5 treatments/season:
max.
2 applications with fenhexamid |
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Spray schedules with 6 and more treatments:
at the maximum one third of all Botryticide-applications |
Mixtures:
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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. |
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| GENERAL
RECOMMENDATIONS FOR THE USE OF SBI FUNGICIDES |
| The SBI fungicides represent one of the
most potent classes of fungicides available to the grower
for the control of many economically important pathogens.
It is in the best interest of all those involved in recommending
and using these fungicides that they are utilised in
such a way that their effectiveness is maintained.
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:
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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. |
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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. |
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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. |
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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. |
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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. |
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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. |
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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. |
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| Guidelines
of the 2000 FRAC Banana Working Group |
For information the actual guidelines that
refer to SBI Fungicides are given below.
2000 FRAC BANANA WORKING GROUP
Guidelines
The following guidelines are made with emphasis
to the Central American and the Philippines banana growing
areas where a decreased sensitivity of Mycosphaerella fijiensis
to the DMIs exists. However, the situation in Central America
has stabilized during the 1996-1999 period.
1. |
Field experience in bananas in Central America has
shown that M. fijiensis can develop resistance to the
DMI fungicides. The DMIs are and will continue to be
very key tools for the efficient control of Black Sigatoka
in bananas. An effective anti-resistance strategy must
be followed when using these materials, in order to
protect their fungicidal performance over the long
term. |
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2. |
In general terms, the use of fungicides with a different
mode of action applied in tank mixtures or in alternated
sprays are both suitable approaches to diminish the
risk of resistance development. These use strategies
are particularly valuable in the case of site specific
systemic fungicides and in situations when there is
a need to cope with a shift towards decreased sensitivity.
The anti-resistance strategies only allow a limited
number of sprays with the systemic fungicides (see
items 9-10). Therefore, the use of these materials
in alternation with fungicides belonging to other classes
seems to be the best approach in order to allow the
necessary total number of sprays which are required
with the systemic fungicides, for efficient Black Sigatoka
control over the whole high pressure period. |
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3. |
The use of the full recommended label rate of DMIs
is strongly urged (straight DMI use). |
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4. |
The DMIs must be used at least ¾ of their
full recommended label rates when they are applied
in tank mix with other systemic fungicides. When tridemorph
is the partner compound, it must be added at least
at 2/3 its commercially recommended label rate . In
the case of tank mixtures with benzimidazoles, these
fungicides must be used at their full recommended label
rates. Finally, when mancozeb is used as the partner
material for site specific systemic fungicides, these
DMIs must be applied at their full recommended label
rates. |
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5. |
Single alternation of DMIs with other
systemic fungicides is recommended. Repeated (sequential)
applications of DMIs (either alone or in tank mixtures
with other systemics) must be limited to no more than
2 consecutive sprays (i.e. block of 2 sprays). The
same recommendation is also applicable to tridemorph. |
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6. |
All the fungicides belonging to the DMI’s class
are considered to be a single product group, amongst
which there is in general some degree of cross resistance.
Therefore, alternation or mixtures of DMIs must not
be recommended for the purpose of resistance management. |
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7. |
The benzimidazole fungicides must not be applied
in consecutive sprays. The applications of benzimidazole
fungicides should not exceed a total of 6 sprays in
a period of 12 months. It is also recommended that
this class of fungicides must be always used in mixtures
with mancozeb. |
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8. |
In the case of straight applications of the DMIs,
the number of sprays against Black Sigatoka must not
exceed a total of 8 cycles during any 12 month period
(a maximum of 6 total sprays in the case of Yellow
Sigatoka). |
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9. |
The maximum number of DMI's sprays for controlling
Black Sigatoka might be increased to a total of 10
applications in a 12 month period, if the DMIs are
always applied in mixtures with other systemics (7
maximum sprays in the case of Yellow Sigatoka ). |
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10. |
The number of tridemorph sprays with this fungicide
used either alone, in mixture with the DMIs or other
classes of fungicides must not exceed a total of 12
applications within a 12 month period. |
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11. |
Protective (preventative) fungicides are considered
to be a very valuable and necessary tool for the banana
Sigatoka control programs. |
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12. |
The systemic fungicides must only be applied in oil
or oil-water emulsions |
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13. |
A DMI- free period of at least 2 (and if possible
3-4) consecutive months, during the periods of lower
disease pressure is recommended. |
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14. |
DMIs should be applied to achieve as early a curative
control as possible. |
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15. |
Eradicative use of DMIs should be avoided. |
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