The effect of fungicide programmes based on epoxiconazole on the control and DMI sensitivity of Rhynchosporium secalis in winter barley

Abstract

To prolong the effective life of the newer, more active DeMethylation Inhibitor (DMI) fungicides, two-spray programmes were evaluated for their effectiveness in combining good control of rhynchosporium on winter barley with prevention of the build-up of DMI-resistant pathogen strains. Programmes were based on the DMI epoxiconazole alone or in combination or alternation with three partner fungicides with different modes of action, fenpropimorph (a morpholine), cyprodinil (an anilinopyrimidine), azoxystrobin (a QoI/strobilurin fungicide). In the majority of six field trials in Northern Ireland and South-west England (1998–2000), DMI sensitivity of Rhynchosporium secalis isolates was lower after fungicide treatment than before and the least sensitive isolates came from the plots treated with two half-rate applications of epoxiconazole alone. All fungicide programmes reduced disease compared with the untreated control. Epoxiconazole used alone gave the poorest disease control, but did increase the yield. The three partner fungicides all improved disease control and yield; two applications of half-rate epoxiconazole with half-rate azoxystrobin or cyprodinil performed best overall. With the range of pathogen sensitivities found in the present study, a DMI such as epoxiconazole remains a useful component of a control programme for R. secalis, but should be supplemented by a partner fungicide with a different mode of action such as a strobilurin or anilinopyrimidine.