Plant pathologists are assessing the threat of cercospora leaf spot as an emerging disease of faba beans.

Rohan Kimber of the South Australian Research and Development Institute (SARDI) told a faba bean symposium at Darlington Point in southern New South Wales in March that the disease is becoming more prevalent in the southern growing regions.

Mr Kimber however said resistance genes had been identified and were included in current breeding programs.

The disease is associated with cold, wet conditions and the spores are spread by rain splash.

Symptoms, which may be confused with those associated with aschocyta blight, usually occur on the lower leaves first. Mr Kimber said that as a point of differentiation, cercospora leaf spot lesions don't have the distinctive black pin dot-like fruiting bodies associated with aschocyta blight.

As with a number of other bean diseases, stubble from the preceding bean crop is the source of infection and a four-year rotation is recommended as a control measure.

Mr Kimber said that anecdotal evidence suggested that some fungicides may be effective against the disease, though the impact on yields needed to be determined by further research.

He said while there was no direct evidence that the disease impacts on yields, it has made its presence felt among growers in south-eastern Australia and it has been determined that most faba bean cultivars currently in use are susceptible.