Black spot on pea increases in South Australia

Black spot infection in field peas growing in South Australia has been high this season [2009], especially in early-sown crops. According to SA Research and Development Institute [SARDI] Jenny Davidson, the high level of infection is due to several reasons.

"Black spot spores were released in June [2009], which is later than in most years, leading to high spore numbers infecting seedling crops," Ms Davidson said. "Early-sown crops had the most exposure to these spores and so have more disease. The disease has been increased by the frequent rain events during July [2009], which splashed the infection from the base of the pea plants to the higher nodes."

On top of the high infection loads, some pea crops have been sown into paddocks that had peas in 2005. "Black spot was severe in the spring of 2005 and produced a spore load that has survived in the soil. This spore load has been splashed by the frequent rain onto the current seasons crop. In addition, plant injury through herbicide application may have exacerbated disease levels," Ms Davidson said.

She said fungicide sprays to reduce black spot severity could be economic. Sprays should be timed ahead of a major rain event to minimise spread of the disease during rainfall. Black spot will not spread in dry conditions.