Botrytis infection warnings in strawberry: reduced enhanced chemical control.

The fungal pathogen Botrytis cinerea is the causal agent of grey mould, the most important fungal fruit rot disease in strawberry in Europe. Currently disease control for grey mould is based on preventive spraying every five to seven days during flowering and harvest. Replacing preventive spraying with applications based on infection warnings can optimize performance and reduce the amount of sprays needed. Success of this approach will depend on the accuracy of the model used to predict disease outbreak. For this reason three infection models (BOTEM, BoWaS, DSS-Italy) were evaluated during the growth seasons of 2003 and 2004. The experiments included June bearing, retarded June bearing and ever bearing strawberries. In all experiments the use of infection models leaded to a reduced number of fungicide applications. However the efficacy of the different models towards the control of B. cinerea also decreased compared to the efficacy obtained with a standard 7 day schedule. Best results were obtained with BOTEM, developed by HRI (Horticultural Research International, East-Malling, UK): 17-60% reduction in fungicide use and an efficacy between 66-93 depending on the growth season, culture practice and the fungicides used. Compared with routine preventive spraying, the Botrytis fruit rot percentage is slightly higher. A higher efficacy with Botrytis infection warnings can only be obtained if infection warnings change from curative to preventive. A retroactive evaluation of a preventive warning system was included. Making use of the 48h weather forecasts supplied by the Royal Meteorological Institute of Belgium (KMI) based on ALADIN for the region of Haspengouw, it was possible to replace 30 up to 100% of the curative application by preventive spraying depending on the experiment and the threshold set for the preventive model.