Lawson cypress is a valuable ornamental shrub widely used in landscape design. This study investigated root rot symptoms observed in Guilan Province. The causal agent was isolated and identified as Fusarium solani through morphological and molecular analyses, representing the first report of this pathogen on Lawson cypress in Iran (NCBI accession PV077970). To evaluate management strategies, the antifungal effects of twelve plant essential oils were tested in vitro using disk diffusion and medium incorporation methods at multiple concentrations. Five chemical fungicides, including mancozeb, thiophanate-methyl, Bordeaux mixture, copper oxychloride, and Rovral-TS, were applied at 2000 ppm for comparison. Results showed that thyme, ajowan, and ziziphora essential oils exhibited the strongest inhibition in disk diffusion assays, while savory, thyme, and ajowan oils completely suppressed mycelial growth in medium incorporation, comparable to Rovral-TS, thiophanate-methyl, and copper oxychloride. In spore germination tests, Bordeaux mixture achieved 100% inhibition, followed by thyme oil with 67.7%. Evaluation of fungicidal and fungistatic activity revealed that thyme and ajowan oils, along with thiophanate-methyl and Rovral-TS, had fungicidal effects, whereas ziziphora and copper oxychloride were fungistatic. This study provides the first evidence of F. solani causing root rot in Lawson cypress in Iran and offers a comprehensive assessment of essential oils as natural antifungal agents. The results highlight thyme and ajowan oils as promising, eco-friendly alternatives to chemical fungicides, supporting safer and sustainable disease management in ornamental plants.