Effects of fungicides used to control Rhynchosporium secalis where benzimidazole resistance is present

Abstract

The effects of fungicides used to control Rhynchosporium secalis in winter barley were investigated in five field trials in Co. Down, Northern Ireland. Benzimidazole resistance was present in the R. secalis population of each site. Fungicide performance was evaluated in terms of disease control, maintenance of green leaf area, grain yield and grain quality. Samples of R. secalis isolates taken before and after treatment in each field were assessed for sensitivity to carbendazim in the laboratory. Carbendazim contributed little to disease control, the maintenance of green leaf area, grain yield or grain quality. Carbendazim was associated with a significant increase in disease severity in some plots. Treatments containing carbendazim, either alone or in mixture, caused an increase in the proportion of carbendazim-resistant isolates within R. secalis populations. Propiconazole-containing treatments performed well in terms of disease control, maintenance of green leaf area and grain quality. They caused no change in carbendazim resistance frequency.