Amendment of potato-dextrose agar with grapefruit extract at dose 40μg/cm3 inhibited linear growth of Phytophthora cryptogea about 50%. At such concentration of the product in soil leachate formation of zoosporangia was inhibited about 95%. Application of grapefruit extract as peat drench reduced population density of the pathogen about 80% and this high activity was observed at least 30 days.