Nematicidal activity of essential oils extracted from 27 spices and aromatic plants were evaluated in vitro and in pot experiments. Twelve of the twenty-seven essential oils immobilized more than 80% of juveniles of the root-knot nematode Meloidogyne javanica at a concentration of 1,000 mul/liter. At this concentration, most of these oils also inhibited nematode hatching. Essential oils of Carum carvi, Foeniculum vulgare, Mentha rotundifolia, and Mentha spicata showed the highest nematicidal activity among the in vitro tested oils. These oils and those from Origanum vulgare, O. syriacum, and Coridothymus capitatus mixed in sandy soil at concentrations of 100 and 200 mg/kg reduced the root galling of cucumber seedlings in pot experiments. The main components of these essential oils were tested for their nematicidal activity. Carvacrol, t-anethole, thymol, and (+)-carvone immobilized the juveniles and inhibited hatching at >125 mul/liter in vitro. Most of these components mixed in sandy soil at concentrations of 75 and 150 mg/kg reduced root galling of cucumber seedlings. In 3-liter pot experiments, nematicidal activity of the essential oils and their components was confirmed at 200 and 150 mg/kg, respectively. The results suggest that the essential oils and their main components may serve as nematicides.
Essential oils from oregano and thyme were applied for 24 h as fumigants against the mycelia and spores ofAspergillus flavus, Aspergillus niger and Aspergillus ochraceus, as well as against natural microflora of wheat grains. The minimal inhibitory concentration (MIC) of oregano oil needed to inhibit the mycelial growth of the fungi was 2.0 μl/L, while spores were eradicated following exposure to 2.0 to 2.5 μl/L. The thyme essential oil was less efficient in controlling mycelia and growth was observed even following exposure to 4.0 μl/L. However, the thyme essential oil was fungitoxic to spores (MIC = 3.0 μl/L). In another set of trials the efficacy of the oils and two of their constituents (carvacrol and thymol) in controlling natural microflora of surface-sterilized wheat grain was studied. Of the four materials investigated, only oregano essential oil exhibited fungicidal activity and, following 24 h exposure to 20 μl/L, a significant reduction in the percent of infested grain was observed even after 5 days of incubation on potato dextrose agar. A reduction in the germinability of the grains was evident following exposure to the materials tested. When the fungicidal activity of oregano essential oil was evaluated using grains with different moisture contents (MC), data revealed that the better inhibitory effect was achieved in grain with a high MC. The findings emphasize the toxicity of oregano and thyme essential oils as fumigants against fungi attacking stored grain and strengthen the possibility of using them as an alternative to chemicals for preserving stored grains.
The fumigant toxicity of 28 essential oils extracted from various spice and herb plants and some of their major constituents were assessed for adult coleopteransRhyzopertha dominica, Oryzaephilus surinamensis, Tribolium castaneum, andSitophilus oryzae. Three groups of active materials were distinguished: (1) The compounds terpinen 4-ol, 1,8-cineole, and the essential oils of three-lobed sage, sage, bay laurel, rosemary, and lavender were most active againstR. dominica; (2) The compounds linalool,α-terpineol, and carvacrol and the essential oils of oregano, basil, Syrian marjoram, and thyme were most active againstO. surinamensis; and (3) the compound 1,8-cineole and the essential oils anise and peppermint were active againstT. castaneum.
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