Light leaf spot (Pyrenopeziza brassicae): a resurgent problem in the UK

Since 2006, the incidence and severity of light leaf spot (Pyrenopeziza brassicae) in winter oilseed rape in the UK has increased so that the disease is now the main disease concern for growers with respect to yield loss. For example, in the springs of 2011, 2012 and 2013, > 70% of crops and > 30% of plants surveyed in England were affected by the disease. Crops have been severely affected in southern England as well as further north. It is thought that the increase in the prevalence of light leaf spot may be due to factors such as recent unusual weather conditions, a lack of resistance in currently grown varieties and poor disease control from poorly timed fungicide applications. Seasonal guidance for growers has been provided for more than 10 years by the on-line light leaf spot forecast but there is a need to refine predictions of epidemic onset in autumn to improve fungicide timing and overall disease management. National survey data highlight the need for new research to investigate the reason for this change in disease prevalence. This paper describes our current understanding of light leaf spot and work to be done in two new projects. One project aims to investigate pathogen development/epidemic onset in autumn and the role of subsequent components of the epidemic in epidemic progression. The other (PhD) project aims to investigate aspects of the light leaf spot pathogen populations with respect to improving varietal resistance