| Summary: | The effect of 10 essential oils (basil, thyme, pine needle, geranium, orange, rosemary, grapefruit, lavender, peppermint, sage) were tested in vitro against Pyfhium ultimum. Oils of thyme, lavender and sage were most efficient and were selected to be used in in vivo experiments. Minimum Inhibitory Concentration (MIC) was established at 400 μLL-1 for thyme and 700 μLL-1 for sage and lavender. The effect of essential oil volatiles and of the direct contact of the oils with the fungus were also tested and were found to have detrimental effects on its hyphae. The appropriate dose of oil solution was tested in vivo on tomato seedlings growing in plug trays, using suspensions of 700, 7000, 14000 and 35000 μLL-1. Best results were given by the two smallest doses and especially of thyme. The optimum time of application was also established, to no more than two days after sowing. Oils were also applied to tomato seeds as seed coating at rates of 700, 7000 and 14000 μLL-1, with very good results for all oils in the two smallest doses. Treating tomato seedlings prior to transplant was attempted with the root-dipping method, using two different essential oil concentrations (350 and 700 μLL-1), which gave satisfactory results but can cause some stress to the roots. Oil solutions (700 μLL-1) were applied to non- cultivated, infected soil with P. ultimum oospores, in an effort to disinfect soil. Thyme oil was the most effective, when the fungus did not have time to proliferate in the soil and where there were no tomato exudates present. A final method of soil disinfestation was tested, with the combination of soil solarization with essential oils, which gave significant results for all the oils used.
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