Sclerotinia risk live-reporting system for oilseed rape

This project aimed to combine forecasting and monitoring approaches to provide a sclerotinia disease risk reporting system for oilseed rape. It had two specific objectives:

1. To provide forecast alerts and reports of infection-risk factors during the flowering phase. Such information can help guide the timing of the first fungicide application and establish the need for and timing of a subsequent application.
2. Demonstrate that the forecasting and risk evaluation scheme provided improved control of sclerotinia disease with an economic benefit.

The project recorded sclerotinia infection risk factors at 15 sites (including six AHDB Monitor Farms) across England and Scotland during 2015–18. Records included 48-hour forecast weather data, crop growth stage and the amount (percentage) of petals that tested positive for sclerotinia. Five of the 15 sites had Burkard traps to detect airborne spores. Seven of the 15 sites (BASF) included monitoring of sclerotial germination. Three of the 15 sites (ADAS, two sites, and Velcourt) included a fungicide timing trial. Forecast weather and crop growth stage data were used to provide updates three times a week for each site for conditions conducive to infection by sclerotinia: temperatures > 7^oC and RH > 80% for >23 consecutive hours. Data from 2010–17 (including results from a 2010–12 AHDB-LINK project) were also analysed. Key messages are:

• Weather-based infection alert dates aid fungicide timing. Good control of sclerotinia was achieved from fungicides applied before a forecast weather alert.
• Under high disease pressures, fungicides applied in response to alerts resulted in an average yield response of 0.3 t/ha (compared to the untreated control). Where sprays were made at early flower (in the absence of alerts), average yield responses were reduced to 0.22 t/ha.
• Inoculum levels on petals and in the air (from spore traps) help to indicate infection risk.
• The most reliable predictor of low-infection risk was inoculum. When inoculum is zero, infection risk is zero. Positive inoculum indicates risk, but variable infection.
• Combining inoculum with weather alerts provides the greatest potential reduction in the number of sites needing a fungicide treatment.
• Use of the alert scheme based on weather and inoculum resulted in 26% fewer crops treated.
• Infection alerts from a weather-based model and in-field inoculum tests are useful for fungicide timing guidance at a local level.
• Air sampler inoculum data is helpful for regional forecasts and, in association with site-specific weather alerts, to provide fungicide timing guidance.
• The infection alerts are risk averse, and overestimate the risk of high sclerotinia incidence.