Sensitivity of Septoria to triazoles in Denmark Karin Thygesen Lise Nistrup Jørgensen Danish Institute of Agricultural Sciences, Flakkebjerg Lisa Munk.

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

UniversityT98_2_Septoria_triazoles

Background

Septoria tritici

(wheat leaf blotch)

Increased resistance in the fungicide groups of strobilurins and triazoles

T98_2_Septoria_triazoles

Source, Ulrich Gisi, Syngenta

Sensitivity shifts caused by triazols

2,5

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2003 2004

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Spring

Summer

Increased strobilurin resistance, 2003 og 2004 in Danmark

Necessary to focus on spray strategies that may minimize resistance development towards triazoles

Background (cont.)

T98_2_Septoria_triazoles

1. fungicide mixtures

2. reduced number of spray applications

3. correct dosage

4. protectant spraying

Background (cont.)

Strategies that generally reduceresistance development:

T98_2_Septoria_triazoles

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 T98_2_Septoria_triazoles

Method

T98_2_Septoria_triazoles

gs 31 gs 37-39 gs 41-51 gs 55-62

1 0,2 l Opus Team - 0,2 l Comet +

0,4 l Opus

-

2 0,2 l Opus Team 0,4 l Opus

- 0,4 l Opus

3 0,2 l Opus Team 0,2 l Comet +

0,4 l Opus

- 0,2 l Comet + 0,4 l Opus

4 untreated untreated untreated untreated

Spray strategies in field experiments at two localities:

Kragelund and Flakkebjerg, 2004

T98_2_Septoria_triazoles

K

K

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21 25 29 30 31 32 37 39 49 51 59 61 -69 71-92

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

Sampling of leaves:

T98_2_Septoria_triazoles

Agar + epoxiconazole

Sporesuspension of pure-cultured isolates

Microtitreplade with different fungicide concentrations mixed with agar

Assessment of sensitivity of Septoria to epoxiconazole using EC50-value

0

0,3

0,03

0,01

0,1

1

10

ppm/L•Estimation of EC50-value

•The lower the EC50-value, the higher sensitivity of the isolate

•Pureculturing of 500 isolates

T98_2_Septoria_triazoles

Results

T98_2_Septoria_triazoles

Sensitivity levels at Flakkebjerg (EC50)

    4th leaf gs 55 

3rd leafgs 55 

Treatment Spray strategy EC50(median)

EC50(median)

2  2 × 0,4 l Opus (gs 37-39+55-62)

- 0,18 a

  2 × (0,4 l Opus + 0,2 l Comet)(gs 37-39+55-62)

-

4 

0,11 b

For each spray strategy, 0,2 l/ha Opus Team was applied at growth stage 31.

untreated

3 0,16 a

0,13 a

T98_2_Septoria_triazoles

Sensitivity levels at Kragelund (EC50)

    4th leaf gs 55 

3rd leafgs 55 

Flag leafgs 73 

Treatment Spray strategy EC50(median)

EC50(median)

EC50(median)

1 0,4 l Opus + 0,2 l Comet (gs 41-51) 

- - 0,22a

2 2 × 0,4 l Opus (gs 37-39+55-62) 

- 0,29a 0,29a

3 2 × ( 0,4 l Opus + 0,2 l Comet)(gs 37-39+55-62) 

- 0,30ab 0,33b

4 untreated 0,25a 0,19a 0,09c

For each spray strategy, 0,2 l/ha Opus Team was applied at growth stage 31. T98_2_Septoria_triazoles

Sensitivity levels using pure Opus sprayings

0,25a 0,19aubehandlet

No sensitivity shifts at 3 sprayings compared to two sprayings, using pure Opus sprayings

K

k

k

T98_2_Septoria_triazoles

Sensitivity levels at Kragelund (EC50)

    4th leaf gs 55 

3rd leafgs 55 

Flag leafgs 73 

Treatment Spray strategy EC50(median)

EC50(median)

EC50(median)

1 0,4 l Opus + 0,2 l Comet (gs 41-51) 

- - 0,22a

2 2 × 0,4 l Opus (gs 37-39+55-62) 

- 0,29a 0,29a

3 2 × ( 0,4 l Opus + 0,2 l Comet)(s 37-39+55-62) 

- 0,30ab 0,33b

4 untreated 0,25a 0,19a 0,09c

For each spray strategy, 0,2 l/ha Opus Team was applied at growth stage 31. T98_2_Septoria_triazoles

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

Sensitivity levels at sprayings with a mixture of Opus and Comet

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

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

T98_2_Septoria_triazoles

    Kragelund Flakkebjerg

    3rd leafgs 55 

Flagleafgs 73 

3rd leafgs 55 Treatment Spray strategy Percent

septoriaPercent septoria

Percent septoria

1 0,4 l Opus + 0,2 l Comet(gs 41-51) 

- 1,78a -

2 2 × 0,4 l Opus (gs 37-39+55-62) 

16,4a 2,28a 11,18a

3 2 × (0,4 l Opus + 0,2 l Comet)(gs 37-39+55-62) 

10,42b 1,01b 9,09b

4 untreated 31,42c 15,31c 14,98c

Disease level of Septoria

T98_2_Septoria_triazoles

• 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

Consequence of sensitivity shifts

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Drift in triazole field performance?

2003

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1995-97

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Change of field effect on septoria from triazoles (Opus) in UK

Source: Bill Clark ADAS T98_2_Septoria_triazoles

Change of field effect on septoria from triazoles in Denmark

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91 92 93 94 95 96 97 98 99 0 01 02 03 04 05

% c

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Tilt top 0,33

Opus team 0,5

Potens (Tilt top 0,33)

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

T98_2_Septoria_triazoles

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.

T98_2_Septoria_triazoles