in this work, the effect of ultrasonication time on the particle size of thyme essential oil nanoemulsion was determined. The results showed that the particle size resulting from sonication for 15 minutes was around 207.2 nm, and TEM study revealed the spherical shape. The particle size in preparation subjected to sonication for 60 min was decreased to 34.6 nm and they were spherical and shapeless. The in vitro experiments revealed that the nanoemulsion at different concentrations (0.25 – 3.0%) was capable of adversely affecting the mycelial growth of Sclerotinia sclerotiorum. The nanoemulsion (particle size 34.6 nm) completely prevented fungal growth at the lowest concentration. On the other hand, fungal growth was prevented by the 1% concentration of the nanoemulsion of particle size 207.2 nm. Treating fennel seeds with oil emulsion did not affect germinability, while nanoemulsion (34.6 nm) prevented feed gemination when used at 1.0 concentration and the nanoemulsion of 207.2 nm particle size was less inhibitive though a sharp decrease at 1.0% concentration occurred. Percentages of damping off were significantly reduced and plant growth was improved as well as the activities of peroxidase and polyphenol oxidase were increased as a result of treatment with namoemulsion.