Abstract In certain plant species, essential oils have been reported to inhibit seed germination and cause toxicity and have been associated with a loss of photosynthetic activity. This study aimed to evaluate the effects of essential oils and their major compound citronellal on the germination and growth of crabgrass ( Digitaria horizontalis ) and burrgrass ( Cenchrus echinatus ). Essential oils from E. citriodora and C. nardus and pure citronellal compound were used at concentrations of 1% and 10% and 20% to test seed germination and phytotoxic effects, respectively, in the plants. The treatments application was done when the plants were at the four-leaf stage. Seed germination was reduced drastically (97–99% reduction relative to untreated controls), with citronellal showing more drastic reductions than essential oils. In addition, evaluated the phytotoxic effects of essential oils on plant height and dry mass of shoots and roots were evaluated. The negative effects of the oils were seen 12 h following the treatment. The application of the oils at a concentration of 20% reduced the accumulation of dry mass of shoots and roots; however, the number of tiller only affected stomatal opening in burrgrass. Finally, the oils reduced chlorophyll and total protein content in the weeds by more than 80% and 90%, respectively. Therefore, these oils may have application as potential bioherbicides to controlling weeds.