Effects of temperature and wetness duration on infection of winter oilseed rape leaves by Pyrenopeziza brassicae

Light leaf spot, caused by Pyrenopeziza brassicae Sutton and Rawlinson (anamorph Cylindrosporium concentricum) is responsible for considerable yield losses in winter oilseed rape crops in the UK. A provisional version of a forecasting scheme based on disease survey data, which will guide farmers in taking spray decisions, has been produced [1]. To improve this forecasting scheme, more specific knowledge about effects of the environment on the development of light leaf spot epidemics is necessary. It is likely that epidemics are initiated by primary infections resulting from wind-dispersed ascospores and that further epidemic progress is mostly dependent on infections from splash-dispersed conidiospores. Therefore, a better understanding of the criteria for infection for both spore types will provide useful information to improve the forecasting scheme. The effects on infection of leaf wetness duration and temperature and their interactions are being studied. Information is available about effects of leaf wetness duration on infection by conidiospores at 12 and 18°C [2], but these temperatures rarely occur during winter in the UK, The criteria for infection by conidiospores at lower temperatures have never been studied