Black rot (BR) and Botrytis bunch rot (BBR), caused by the hemibiotrophic fungus Guignardia bidwellii (Ellis) and the necrotrophic fungus Botrytis cinerea, respectively, are two major diseases of grapevine responsible for severe crop losses. The scarce number of available and efficient biocontrol solutions against these pathogens results in an urgent need to develop sustainable control strategies. Within the framework of the French research project VITAE, this study aimed at evaluating and comparing the efficacy of two plant defense elicitors, Methyl Jasmonate and COS-OGA. They were evaluated either in greenhouse conditions, via in planta efficacy bioassays against BR, or in controlled laboratory conditions on detached leaves against BBR. COS-OGA (200 mg/l), when applied preventively twice, displayed promising protection rates, ranging from 50 % up to 73 %, against both BR and BBR. Conversely, MeJA application resulted in a very limited efficiency, against both pathogens. These results indicated that COSOGA may be promising notably for the control of BR, but further studies should confirm its efficacy, especially under field conditions