Fungicide programmes for effective control of Rhynchosporium on winter barley


Cereals & Oilseeds
Project code:
01 April 1998 - 31 March 2002
AHDB Cereals & Oilseeds.
AHDB sector cost:
£100,715 from HGCA (project 1181).
Project leader:
L R COOKE1 and T LOCKE2 1Department of Applied Plant Science, Queen's University Belfast, Agriculture & Food Science Centre, Newforge Lane, Belfast, Northern Ireland, BT9 5PX 2ADAS Rosemaund, Preston Wynne, Herefordshire, HR1 3PG



About this project


The control of Rhynchosporium (leaf blotch), currently the most economically-important disease of barley, is heavily dependent on fungicides.  The DMI fungicides were the key element of control programmes, but the effectiveness of older DMIs has been impaired by selection of resistant strains.  During the 1990s, MBC-resistant strains of Rhynchosporium secalis developed and these are now too widespread for MBCs to be suitable partners for DMIs in anti-resistance strategies.

To prolong the effective life of the newer, more active DMIs, two-spray fungicide programmes were evaluated for their effectiveness in combining good control of Rhynchosporium with prevention of the build-up of DMI-resistant pathogen strains.  Programmes were based on the DMI epoxiconazole ('Opus') alone or in combination or alternation with three partner fungicides with different modes of action, fenpropimorph ('Corbel', a morpholine), cyprodinil ('Unix', an anilinopyrimidine), azoxystrobin (a strobilurin, 'Amistar').

In a series of field trials in Northern Ireland and South-west England over the three years 1998-2000 performance of programmes was assessed in terms of disease control, prolongation of green leaf area and yield and effects on DMI sensitivity were monitored by testing isolates of the pathogen collected before and after fungicide application.

Across the six trials, all fungicide treatments reduced disease significantly compared with the untreated control.  Epoxiconazole used alone gave the poorest disease control and lowest green leaf area, but did increase yield.  The three partner fungicides all improved disease control and yield.  Programmes based on two applications of half-rate epoxiconazole with half-rate azoxystrobin or cyprodinil performed best overall, cyprodinil being marginally more effective in terms of disease control, while azoxystrobin combinations achieved the best yields.

In the majority of trials, DMI sensitivity of R. 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.  There was no consistent difference in effects on epoxiconazole sensitivity between the three partner fungicides, but all tended to reduce selection for resistance compared with two half-rate applications of epoxiconazole alone.

It is concluded that selection for DMI resistance is continuing to occur in R. secalis, but that use of a partner fungicide helps to slow down the process, while not preventing it.  With the range of pathogen sensitivities found in the present study, a DMI such as epoxiconazole is a useful component of a control programme for R. secalis, but must be supplemented by a partner fungicide.  Fungicides with different modes of action from the DMIs from the strobilurin (QoI) and anilinopyrimidine group are the most effective partners in terms of disease control and yield.