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| Key
Points from meeting |
Generally in 2002 a stable situation
was found with DMI’s and morpholines.
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.
Yellow and brown rust: field performance of DMI’s
remains good.
Barley
Rhynchosporium: Generally stable situation. Reduced
DMI performance reported in Scotland in 2001, however
no sensitivity data available for 2002. Analysis in
progress.
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,
a monitoring programme will be established.
Bananas
Black Sigatoka: 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
Resistant isolates are common in the north of Germany
and present in low frequencies elsewhere. Length of
mildew control reduced in field situations.
Grapes
No change in sensitivity (2001 data) or performance
since introduction in 1999.
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| 2002
Meeting |
FUNGICIDE
RESISTANCE ACTION COMMITTEE
STEROL BIOSYNTHESIS INHIBITOR (SBI) WORKING GROUP
Hosting company: Dow AgroSciences
Venue of the meeting: Heathrow
Business Centre, London, UK
Date: 17th October 2002
Working Group participants present
at the meeting:
| Dr.
K.H. Kuck (Chairman) |
Bayer AG Crop Protection
Business Group, Monheim, Germany |
| Dr. C.
Longhurst (Secretary) |
DowAgroSciences, European Research
and Development, Letcombe, UK |
| F. Kerz-Moehlendick |
Bayer CropScience, Monheim, Germany |
| A. Mehl |
Bayer CropScience, Monheim, Germany |
| Mr. J-M
Gouot |
Bayer CropScience, Lyon, France |
| Dr. I.Gasnier |
DuPont de Nemours (France)
SA, Centre Europeen de R&D |
| Dr. K.
Stoermer |
BASF AG, Crop Protection Division,
Limburgerhof, Germany |
| Dr. O.
Puppin |
Isagro Ricerca, Milano, Italy |
| Dr. A.
Cook |
Syngenta, Jealott´s Hill Research
Centre, UK |
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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 2002 meeting (hosted by Dow AgroSciences) 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 now three classes of fungicides
that comprise the Sterol Biosynthesis Inhibitor's (abbreviated
SBI's): the DMI-fungicides, the so-called "Morpholine"-fungicides
and most recently, the hydroxyanilides. All 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 group
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 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 of the DMI and «morpholine» classes
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". Fenhexamid, the only representative
of hydroxyanilides, shows no cross-resistance to other
Botryticid.
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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 2002 disease pressure was generally low.
Morpholine products performed well when applied
according to label recommendations and performance
was excellent in all regions. Sensitivity was
stable.
Scald (Rhynchosporium secalis)
Moderate infection levels.
Generally stable situation. Reduced DMI performance
reported in Scotland in 2001, however no sensitivity
data available for 2002. Analysis in progress.
Net Blotch (Pyrenophora teres /Drechslera teres)
Disease incidence was moderate in 2002.
Field disease control was generally good with no
problems reported.
No sensitivity data were presented.
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WHEAT DISEASES |
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Wheat powdery mildew
(Blumeria graminis f.sp. tritici / Erysiphe graminis
f.sp. tritici)
Disease pressure was low to medium.
DMIs: Sensitivity data was presented for tebuconazole,
confirming that the situation was generally
stable. A slight increase in sensitivity was
observed in northern Europe, but remained within
the range of variability seen over the last
10 years. 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.
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 high. Good field performance
and generally stable situation (DMI) but with
a slight increase in the frequency of less sensitive
isolates. This is possibly linked to a trend
towards the use of lower dosages of DMIs.
As pointed out in the 'General Recommendations
for Cereals' (see 1.3) split / reduced rate programmes
using repeated applications which provide continuous
selection pressure should be avoided.
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)
No problems reported. Performance of DMI’s
has been maintained. No sensitivity data were
presented. |
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| Quinoxyfen
- |
| 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 alteration or in combination
with fungicides of different modes of action.
A maximum number of 2 applications per season is recommended.
The practical use rates of quinoxyfen should be kept
between 50 and 100 g ai/ha per application.
Quinoxyfen should only be applied in the spring - autumn
applications are not recommended.
NON-CEREAL DISEASES
| |
Grape Powdery Mildew (Uncinula necator)
Disease pressure was moderate. Performance of
DMIs, "morpholines" and quinoxyfen
was good. No efficacy issues in 2002.
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 2002 when compounds were used
according to the manufacturers’ and FRAC
recommendations. No sensitivity data were presented.
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)
Agronomica trials, Italy – poor efficacy
was reported in some trials when triazoles were
used alone. They are starting a monitoring programme
with University of Piacenza. 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.
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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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