Significance of fungicide dose, timing and varietal resistance for controlling light leaf spot (Pyrenopeziza brassicae) in winter oilseed rape

Abstract: Reports of light leaf spot, caused by the fungal pathogen Pyrenopeziza brassicae, in commercial winter oilseed rape crops have been increasing in Scotland, England and Wales. In Scotland, 62% of crops were reported to have light leaf spot symptoms in spring 2015, and in England and Wales 85% of crops were affected. Yield losses caused by light leaf spot in England and Wales were estimated to be in the region of £ 140 million (€ 178 million) despite the majority of crops receiving at least 3 fungicide applications in a single season. Control of light leaf spot is predominately through the application of two spray fungicide programmes, with the first usually in November followed by another fungicide application pre-/at stem extension onwards (usually February/March). Growers in the UK can select varieties based on a range of characteristics described in the Recommended Lists® for Cereals and Oilseeds which are published annually by the Agricultural and Horticultural Development Board (AHDB). Independent information on efficacy and appropriate fungicide doses for disease control including light leaf spot for a range of fungicide modes of action are also available from the AHDB. Despite the integration of such strategies to control crop diseases being encouraged, there is relatively little information available on the benefits these strategies can offer growers. This paper examines data derived from experiments using combinations of fungicide application timing, varietal resistance rating and fungicide dose for light leaf spot control in 2014 and 2015 from Scotland and England. The benefits of using integrated control strategies for control of light leaf spot, as well as the potential impact for control of other diseases, is discussed.