Controlling strawberry powdery mildew with reduced number of fungicide sprays

Abstract

Strawberry powdery mildew (Podosphaera aphanis) is the most feared disease of strawberry under protection, environmental conditions under polythene are ideal for the growth of the fungi, with temperature and relative humidity (RH) affecting fungal development and disease severity. To control P. aphanis growers apply fungicides every 7-14 days throughout the season. A rule-based prediction system was developed which records the accumulated number of hours (up to 144) of disease conducive conditions (temperature 15.5-30°C, RH>60%), both parameters must be satisfied simultaneously for 144 hours to accumulate for pathogen development. The prediction system identifies high risk periods when sporulation can occur enabling growers to spray at the optimal time thus preventing primary infection. A user-friendly web-based system was used on two farms in England and Scotland in 2018 and six farms in 2019. Participating farms used temperature and humidity sensors in each of the trial fields. The decision support system aims to provide commercially satisfactory disease control with fewer fungicide sprays. Growers check daily to follow the accumulation of disease conducive hours, high risk and the need for fungicide spraying occurred between 120 and 144 hours. Following fungicide application, the system was reset, and hours of disease conducive conditions accumulate again. This was compared to an area of the farm that used their routine fungicide spray programme. In both years, growers achieved commercially satisfactory disease control, without epidemic development. Furthermore, each participating grower saved between two and four sprays, compared to their routine spray programme. A cost-benefit analysis based on fungicide and labour costs, indicated savings between £200-£400 per hectare. The use of the prediction system enables growers to spray with precision timing, therefore maximising fungicide efficiency and reducing costs. The system can be used as a decision support system giving confidence to only spray when necessary.