Reducing the impact of Sclerotinia disease: inoculum detection and forecasting fungicide timing in oilseed rape

Abstract: Sclerotinia disease caused by the fungus Sclerotinia sclerotiorum causes significant losses in oilseed rape and other arable and vegetable crops in the UK, with infected crops providing a potential source of infection to subsequent and/or nearby susceptible crop species. Strategies for control are mainly focused on infection from the airborne spores produced when sclerotia germinate, but there is interest in targeting sclerotia in soil as well. This report focuses on improving the timing of foliar fungicide applications, but is part of a larger project on integrated control, also investigating control of the soil-borne phase, the potential for improved control from co-operation between farms, and modelling the effects of rotations. Boscalid with metconazole was applied as single sprays at yellow bud, early-, mid-, and late-flower, and also as two and three spray programmes at combinations of these times, to an oilseed rape trial at ADAS Rosemaund, Hereford, UK 2010. Two forecasting models were adapted for use and tested in-field. A spore infection model based on SkleroPro infection conditions gave approximately 90% control using 48 hr forecast alerts to guide spray timing (two sprays). A germination model predicted a late spray which was less effective. Petal sampling on four occasions during flowering indicated moderate-high inoculum according to agar plate tests. PCR tests on 24 hr Burkard spore trap samples showed that some ascospore inoculum was present earlier than detected on petals or by observations of sclerotial germination, and concentrations increased and peaked during flowering. Forecasting based on weather data may need to be combined with inoculums.