Seasonal variations in the chemical composition of leaves from Agastache rugosa were analyzed by gas chromatography-mass spectrometry (GC-MS). Phytotoxic and antimicrobial activities of its essential oil were investigated by characterizing 31 components, primarily methylchavicol (80.24%), dl-limonene (3.50%), linalool (4.23%), 5-methyl-2-(1-methylethylidene)-cyclohexanone (3.84%), and beta-caryophyllene (2.39%). The contents of most of these chemical constituents varied significantly (P<0.05) over time, with the highest oil yield being early in the growing season (May). Their phytotoxic effects on the seed germination of Majorana hortensis, Trifolium repens, Rudbeckia hirta, Chrysanthemum zawadskii var. latilobum, Melissa officinalis, Taraxacum platycarpum, and Tagetes patula also were determined. These oils partially or completely inhibited germination, and prevented the growth of radicles and hypocotyls. Results of antimicrobial testing showed that the oils also entirely blocked the growth of four microorganisms (Staphylococcus aureus sub. aures, Escherichia coli, Salmonella enteritidis, and Pseudomonas aeruginosa). These inhibitory effects might depend on the activity of methylchavicol, a main compound in A. rugosa.
