Disclosed is a method for modulating a phytopathogenic infection in a plant comprising applying to the plant and/or seeds thereof and/or substrate used for growing said plant an amount of (a) an extract derived from a Reynoutria sp. plant, wherein said extract comprises one or more anthraquinone derivatives that induce plant resistance to phytopathogens, wherein said derivative (i) has the structure as defined in the specification and (b) acibenzolar-S-methyl effective to synergistically modulate the phytopathogenic infection, and wherein synergism is measured by determining E/Ee and E/Ee is at least 1.2
