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 T98_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, pct strobilurin resistance 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 reduce resistance 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 31gs 37-39gs 41-51gs ,2 l Opus Team-0,2 l Comet + 0,4 l Opus - 20,2 l Opus Team0,4 l Opus -0,4 l Opus 30,2 l Opus Team0,2 l Comet + 0,4 l Opus -0,2 l Comet + 0,4 l Opus 4untreated Spray strategies in field experiments at two localities: Kragelund and Flakkebjerg, 2004 T98_2_Septoria_triazoles

KKKKKKKKKKKKKKKKKKKKKKKK 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, 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 leaf gs 55 Treatment Spray strategyEC50 (median) EC50 (median) 2 2 × 0,4 l Opus (gs ) - 0,18 a 2 × (0,4 l Opus + 0,2 l Comet) (gs ) - 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 leaf gs 55 Flag leaf gs 73 Treatment Spray strategyEC50 (median) EC50 (median) EC50 (median) 10,4 l Opus + 0,2 l Comet (gs 41-51) --0,22a 22 × 0,4 l Opus (gs ) -0,29a 32 × ( 0,4 l Opus + 0,2 l Comet) (gs ) -0,30ab0,33b 4untreated0,25a0,19a0,09c 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 0,25a0,19a ubehandlet No sensitivity shifts at 3 sprayings compared to two sprayings, using pure Opus sprayings K k T98_2_Septoria_triazoles

Sensitivity levels at Kragelund (EC50) 4th leaf gs 55 3rd leaf gs 55 Flag leaf gs 73 Treatment Spray strategyEC50 (median) EC50 (median) EC50 (median) 10,4 l Opus + 0,2 l Comet (gs 41-51) --0,22a 22 × 0,4 l Opus (gs ) -0,29a 32 × ( 0,4 l Opus + 0,2 l Comet) (s ) -0,30ab0,33b 4untreated0,25a0,19a0,09c 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

KragelundFlakkebjerg 3rd leaf gs 55 Flagleaf gs 73 3rd leaf gs 55 Treatment Spray strategyPercent septoria Percent septoria Percent septoria 10,4 l Opus + 0,2 l Comet (gs 41-51) -1,78a- 22 × 0,4 l Opus (gs ) 16,4a2,28a11,18a 32 × (0,4 l Opus + 0,2 l Comet)(gs ) 10,42b1,01b9,09b 4untreated31,42c15,31c14,98c 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? 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 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