Evaluation of economic fungicide strategies for control of ascochyta blight in field pea in southern Australia

The aim of this five-year study was to identify economic fungicide treatments to control ascochyta blight in field pea in southern Australia. Results showed a complex interaction between a number of factors. There were clear patterns in efficacy of different fungicides in controlling disease however grain yield and financial gains were dependent on fungicide costs, seasonal conditions and yield potential. Disease suppression was achieved at early growth stages with fungicides applied as seed dressings or via fluid injection before sowing. Foliar fungicides were applied before or at canopy closure growth stage and early flowering. The foliar fungicides prothioconazole plus bixafen, azoxystrobin plus cyproconazole and pyraclostrobin were economic where grain yield was above 1.6 t ha− 1 but mancozeb, the traditional protectant fungicide for field pea, was not economic even where disease severity was reduced. Analysis of grain yield responses to ascochyta blight identified three groupings based on maximum grain yield potential and found ascochyta blight had greatest impact on grain yield in higher rainfall and higher yielding situations. In dry growing seasons with yield potential below 1.6 t ha− 1 the disease had no significant effect on grain yield and no fungicide strategy was economic irrespective of the disease control. A sowing date experiment confirmed that modern semi-leafless ‘afila’ erect field pea varieties are better suited to the combination of early sowing and economic disease management strategies to maximise grain yield in southern Australia than traditional conventional trailing types and have made redundant the advice to delay sowing as a means to avoid ascochyta blight.