Journal of Plant Pathology Archive

Abstract:

Sensitivity of Septoria tritici towards the fungicides trifloxystrobin, folpet, chlorothalonil, propiconazole, prochloraz, tebuconazole, epoxiconazole, and prothioconazole was tested in a bioassay using strains isolated in 1999, 2004, or 2008 in the high-disease-pressure and high-fungicide-input area between the North and Baltic Seas. The percentage of sprays containing at least one demethylation inhibitor (DMI, azoles) was never lower than 60% at any given point of time in the region where the fungal strains were sampled. Quinone outer binding site inhibitor (QoI) use was almost negligible in 1999, increased to about 80% in 2002, and subsequently decreased to 4% in 2008. The bioassay accurately detected the total loss of sensitivity of S. tritici towards trifloxystrobin as a representative of the QoIs that was previously reported. DMI concentrations inhibiting fungal growth by 50% (EC50s) decreased on the average by 48±17% between 1999 and 2004, and increased by 132±42% between 2004 and 2008 compared to 1999. EC50s of the multi-site inhibitors folpet and chlorothalonil increased by 128±25% between 1999 and 2004, and decreased by 40±11% between 2004 and 2008, but changes over time were non-significant for the multi site inhibitors. The period of QoI use approximately coincided with a small but consistent decrease of EC50s for all DMIs tested and with a small but consistent increase of EC50s for the multi site inhibitors.