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

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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

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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

T98_2_Septoria_triazoles

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

T98_2_Septoria_triazoles

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