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| Key
Points from meeting |
Generally in 2001 a stable situation
was found with DMI’s and morpholines.
Wheat
Powdery mildew: stable situation (DMI and morpholine)
Septoria tritici: stable situation (DMI)
Yellow and brown rust: field performance of DMI’s
remains good.
Eyespot: Prochloraz: stable situation. Generally W-type
still increasing in frequency.
Barley
Rhynchosporium: Generally stable situation. Reduced
DMI performance reported in Scotland, however, no sensitivity
changes have been observed.
Net blotch: DMI performance unchanged.
Powdery mildew: stable situation (DMI and morpholine)
Vines
Powdery mildew: performance unchanged (DMI and morpholine).
Apples
Scab: DMI sensitivity and performance unchanged.
Powdery mildew: DMI performance unchanged.
Bananas
Black Sigatoka: DMI sensitivity and performance unchanged.
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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.
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.
"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 D 8 ® D 7 isomerase and the D 14 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.
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 independant 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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1. |
Barley Powdery Mildew
(Blumeria graminis f.sp. hordei / Erysiphe graminis
f.sp. hordei)
In 2001 disease pressure was generally low to
moderate.
DMIs
DMI’s performed as expected.
"Morpholines"
Morpholine products performed well when applied
according to label recommendations and performance
was excellent in all regions. Sensitivity was
stable. |
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2. |
Net Blotch (Pyrenophora teres /Drechslera teres)
Disease incidence was low in 2001.
Field disease control was generally good with no
problems reported. |
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3. |
Scald (Rhynchosporium secalis)
Disease pressure was high in 2001.
The performance of DMI’s was generally acceptable,
when used according to manufacturers’ recommendations.
Sensitivity was stable.
Decreased field performance in Scotland has been
reported, however, no correlation with changes
in sensitivity could be established. Further investigations
are underway.
It is recommended that mixtures with effective
non-DMI fungicides be used for disease control
and that curative treatments should be avoided. |
WHEAT DISEASES |
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1. |
Wheat powdery mildew
(Blumeria graminis f.sp. tritici / Erysiphe graminis
f.sp. tritici)
Disease pressure was low to medium.
"Morpholines"
The sensitivity pattern has remained stable in
all monitored countries over several years.
Field performance of morpholine based products
was good.
DMI's
Sensitivity data was presented for tebuconazole,
confirming that the situation was generally
stable. A slight decrease in sensitivity was
observed in northern Europe, but remained within
the range of variability seen over the last
10 years.
Performance of DMI based products was as expected. |
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2. |
Wheat Brown Rust (Puccinia recondita) Disease pressure was high. As in previous years,
DMI fungicides continued to provide excellent disease
control. |
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3. |
Wheat Yellow Rust (Puccinia striiformis)
As in previous years, DMI fungicides continued
to provide good disease
control.
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4. |
Wheat Leaf Spot (Mycosphaerella graminicola / Septoria
tritici)
Disease pressure was moderate and sensitivity
was stable.
Effective DMI’s continued to provide good
disease control. |
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5. |
Wheat Glume Blotch (Stagonospora nodorum = Septoria
nodorum)
Good control with DMIs was obtained.
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6. |
Wheat Eyespot (Tapesia spp. / Pseudocercosporella
herpotrichoides)
Disease pressure was moderate (U.K., Germany)
to high (France). Efficacy levels of prochloraz
were maintained. The frequency of W-type isolates,
which are more sensitive to prochloraz, continues
to increase. |
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| NON-CEREAL
DISEASES |
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1.
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Grape Powdery Mildew (Uncinula necator)
Disease pressure was moderate across Europe. Performane
of DMIs and "morpholines" was good.
Recommendations:
DMI´s should only be used as preventative
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 DMI'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. |
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2.
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Apple Scab (Venturia inaequalis)
The performance of DMI’s was good on this
disease in 2001 when compounds were used according
to the manufacturers’ and FRAC recommendations.
The sensitivity situation was stable.
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. |
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3.
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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. |
4. |
Sugar Beet Leaf Spot (Cercospora beticola)
Disease control in 2001 remained good; the general
recommendations for resistance management of SBI’s
should be followed. |
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5.
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Banana Sigatoka (Mycosphaerella fijiensis)
No shifts in sensitivity were seen in data presented
at the Banana-FRAC meeting in February 2000. No
problems were encountered with controlling disease
with DMI’s in practice.
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.
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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