Technical Abstract: Individual compounds and ethyl acetate extracts from heartwood of seven conifer species were tested for fungicidal activity against Phytophthora ramorum. Extracts from incense and western redcedar exhibited the strongest activity (EC50 589 and 646 ppm, respectively), yellow-cedar, western juniper, and Port-Orford-cedar showed moderate activity (EC50 1660, 2089, and 2089 ppm, respectively), and no activity was observed for Douglas-fir and redwood. Chemical composition of the extracts varied both qualitatively and quantitatively among the seven conifer species with a total of 54 compounds identified by mass spectrometry. Only three compounds (carvacrol, alpha-terpineol, and delta-cadinene) were identified from more than one species. Of the 14 individual compounds bioassayed, two showed strong activity with an EC50 less than 10 ppm (hinokitiol and thymoquinone), four compounds expressed moderate activity ranging from 11 - 100 ppm (nootkatin, nootkatol, carvacrol, and valencene-11,12-diol), five compounds had weak activity at 101 - 1000 ppm (alpha-terpineol, valencene-13-ol, taxifolin, (+)-beta-cedrene, (-)-thujopsene), and there were three with no activity ((+)-cedrol, delta-cadinene, and methylcarvacrol). All of the most active compounds contained a free hydroxyl group, except thymoquinone. The importance of a free hydroxyl was demonstrated by the tremendous difference in activity between carvacrol (EC50 53.7 ppm) and methylcarvacrol (EC50 >>1,000 ppm).