VALIDATION OF FORECASTING SYSTEMS FOR DOWNY MILDEW AND BOTRYTIS SQUAMOSA IN SPRING SOWN ONION IN FRANCE
Downy mildew caused by Peronospora destructor and Botrytis leaf blight due to Botrytis squamosa are widespread diseases in France. Growers usually spray onions on a preventive weekly basis with fungicides to control them, but this practice may result in unneeded treatments. Research supported by the French National Onion Association was conducted from 1998 and 2001 to validate forecasting models to predict more appropriate application of fungicides on onions in France. After preliminary investigations, different models were chosen to be tested under French climatic conditions: DOWNCAST for downy mildew, and BOTCAST and Blight Alert for Botrytis leaf blight. Four years of testing with trap plants in inoculated field trials led to the validation of DOWNCAST with 88% prediction accuracy while BOTIPIS, a combination of BOTCAST and Blight Alert, was tested with 88.5% prediction accuracy after 2 years. Field trials were also conducted in different areas of France to compare spray programmes based on forecasts with a classical approach. Climatic data required were recorded in the trials with a weather station, and untreated plots were managed to ensure the presence of the diseases. Under these conditions, BOTIPIS reduced the number of treatments by 27 to 78% with no decrease in yield over three years. DOWNCAST allowed a 15 to 29% reduction in the number of anti-mildew applications with no decrease in yield over 2 growing seasons. These models have been available in France as a software programme linked to a weather station for use by onion growers since 2002.
Huchette, O., Guerber-Cahuzac, B. and Brouant, L. (2005). VALIDATION OF FORECASTING SYSTEMS FOR DOWNY MILDEW AND BOTRYTIS SQUAMOSA IN SPRING SOWN ONION IN FRANCE. Acta Hortic. 688, 201-210
Allium cepa, advisory model, foliar disease, Peronospora destructor, DOWNCAST, BOTCAST, Blight Alert