Epidemiology of Botrytis bunch rot in Bordeaux vineyards and alternative control strategies

Abstract: Botrytis bunch rot (BBR) is a major fungal disease of grapevine worldwide caused by Botrytis cinerea. The pathogen presents a complex life cycle in the vineyard with a great genetic variability, multiple biological forms and various infection pathways highly dependent on meteorological conditions. Losses at harvest can be very important quantitatively as well as qualitatively by modifying wine quality from 5% of rotted berries upwards.Extensive research on BBR epidemiology has been carried out at INRA Bordeaux-Aquitaine evaluating and developing disease risk indicators. An interesting case of study is the B. cinerea floral calyptras infection rate as a potential early indicator of disease development and losses at harvest. From 2011 to 2015, B. cinerea infection of calyptras from an experimental Bordeaux vineyard (cv. Merlot) was evaluated at the end of flowering. The potential relationships between the infection on calyptras and the climatic conditions are analysed and discussed. However, no significant correlation was observed between the indicator and BBR disease incidence or severity.Additionally, alternative strategies to chemical fungicides have been evaluated in different Bordeaux organic vineyards in 2015. Natural products, already commercialized for their use in organic viticulture, were applied at key phenological stages or following a disease risk index. Results indicated the reduced interest of a wicker tea product, whereas potassium bicarbonate, kaolin and a fatty acid products showed BBR reduction and may be good candidates as alternative strategies for BBR control.