Sensitivity of Septoria to triazoles in Denmark

1

• Sensitivity of Septoria to triazoles
  in Denmark
• Karin Thygesen
• Lise Nistrup Jørgensen
• Danish Institute of
• Agricultural Sciences,
• Flakkebjerg
• Lisa Munk
• The Royal Veterinary and Agricultural
  University

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Background
Septoria tritici (wheat leaf blotch)
Increased resistance in the fungicide groups of
strobilurins and triazoles
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Background (cont.)
Sensitivity shifts caused by triazols
Increased strobilurin resistance, 2003 og 2004
in Danmark
90
81
80
70
60
50
Spring
pct strobilurin resistance
40
33
Summer
30
22
20
10
2,5
0
2003
2004
Source, Ulrich Gisi, Syngenta
Necessary to focus on spray strategies that may
minimize resistance development towards triazoles
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Background (cont.)
Strategies that generally reduceresistance
development

• fungicide mixtures
• reduced number of spray applications
• correct dosage
• protectant spraying

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Objective of experiment

• Investigations of the fungicide sensitivity of
  the Septoria population at different leaf levels,
  points of time and localities
• The spores of the Septoria fungus disperse from
  the bottom and upwards in the plant
• sampling from different leaf levels enables
  monitoring of sensitivity development over time

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• Method

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Spray strategies in field experiments at two
localities Kragelund and Flakkebjerg, 2004
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K K K K K K K K K K K K
Sampling of leaves
Wheat cv. Ritmo

• Sampling of 4th leaf level from treatment
  without sprayings
• at gs 55
• represent sensitivity of the startpopulationen
• Sampling of 3rd leaf level at gs 55
• populationen after representively 1 and 2
  sprayings
• Sampling of flag leaf level at gs 75
• endpopulationen after termination of sprayings

• Assessment of percent disease

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Assessment of sensitivity of Septoria to
epoxiconazole using EC50-value

• Pureculturing of 500 isolates

Microtitreplade with different fungicide
concentrations mixed with agar
Sporesuspension of pure-cultured isolates
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Agar epoxiconazole
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Results
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Sensitivity levels at Flakkebjerg (EC50)
3
0,16 a
0,13 a
untreated
For each spray strategy, 0,2 l/ha Opus Team was
applied at growth stage 31.
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Sensitivity levels at Kragelund (EC50)
For each spray strategy, 0,2 l/ha Opus Team was
applied at growth stage 31.
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Sensitivity levels using pure Opus sprayings
No sensitivity shifts at 3 sprayings
compared to two sprayings, using pure
Opus sprayings K k k
0,25a
0,19a
ubehandlet
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Sensitivity levels at Kragelund (EC50)
For each spray strategy, 0,2 l/ha Opus Team was
applied at growth stage 31.
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Sensitivity levels at sprayings
with a mixture
of Opus and Comet

• Higher EC50-values at 3 sprayings
  than two sprayings,
  using a mixture which includes
  pyraclostrobin

• Might be caused by Comet selecting for less
• epoxiconazole sensitive isolates

• Might be caused by selection due to highest
  cumulative dosage throughout the growing season

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Disease level of Septoria
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Consequence of sensitivity shifts

• Sensitivity shifts throughout the years are
  relatively limited, compared to how much
  the compounds have been used
• Unclear as to the extent of the shifts, before
  reduced field effects may be expected
• Unclear whether the sensitivity shifts will
  continue or stabilise

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Drift in triazole field performance?
Change of field effect on septoria from triazoles
(Opus) in UK
2005
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Source Bill Clark ADAS
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Change of field effect on septoria from triazoles
in Denmark
Source Lise Nistrup Jørgensen
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Conclusions

• General sensitivity levels (EC50-values)
  ? 0,2-0,3 ppm
• Overall, difficult to say whether sprayings
  generally result in large sensitivity shifts
• Using pure Opus sprayings (Kragelund), no
  increase of sensitivity is seen as result of 3
  sprayings, compared to 2 sprayings
• Using a mixture of Opus og Comet (Kragelund)
  higher EC50-values are seen with 3 sprayings than
  with 2 sprayings

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Conclusions (cont.)

• Sensitivity shifts throughout the years are
  relatively limited, compared to how much the
  compounds have been used
• Unclear as to the extent of the shifts, before
  reduced field effects may be expected
• Resultats from UK show reduced control effects in
  the field
• Too soon to say whether effect changes with Opus
  may occur, since this compound has only been used
  throughout 3 growing seasons.

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