Stemphylium blight in faba bean in 2016

The disease is shown as black spots and marks on green leaves

August 2016

The unusually high incidences of leaf blight symptoms caused by Stemphylium blight have been observed on faba bean crops grown in north-eastern Australia this season.

The blight is characterised by large grey-black necrotic lesions restricted to leaves only, often starting from the leaf edge.

The appearance and distribution of lesions on leaves was quite different from that of chocolate spot, which is considered to be the major leaf blight in the northern region: Chocolate spot typically appears as small discrete reddish-brown lesions on leaves that after extended periods of leaf wetness increase rapidly causing severe leaf necrosis, as well as symptoms on stems, flowers and pods. The symptoms observed this season were also different from other commonly observed leaf blights caused by Ascochyta or Cercospora, both important pathogens on faba bean in Australia’s south-eastern grain growing regions.

The 2016 growing season in the northern region has been relatively mild with a number of low-intensity and long-duration rainfall events that typically favour the development of leaf blights, particularly chocolate spot which was found in a number of early sown crops.

PBA Warda appears to be more susceptible to Stemphylium blight than other varieties including the newest variety PBA Nasma.

Stemphylium blight in faba bean is considered a minor disease and its impact on faba bean yields in the northern region is not yet known. NSW DPI are planning yield loss experiments and will continue variety screening and fungicide efficacy trials, as well as trials to determine whether other (non-genetic) factors (abiotic stresses, herbicide injury, nutrient deficiencies) play a role in increasing the vulnerability of faba bean to this pathogen.

There is little information on the relative value of different fungicides, however it is likely that fungicide application will assist in the control of Stemphylum blight.

Growers are advised to continue with their normal fungicide programs and if concerned about levels of Stemphylium blight seek agronomic advice before making decisions about fungicide application.

More information

  • Joop van Leur at NSW DPI 67631204
  • Bill Manning at North West Local Land Services 0428 607 731