**4. Conclusions**

The obtained results from the study suggested that *Wedelia chinensis* possesses potent phytotoxic effects, repressing the growth of lettuce, alfalfa, cress, rapeseed, barnyard grass, Italian ryegrass, timothy, and foxtail fescue. Two phytotoxic compounds, vanillic acid and gallic acid, were isolated from the aqueous methanol extracts of *Wedelia chinensis*. Vanillic acid and gallic acid significantly impeded the growth of cress and Italian ryegrass seedlings. This is the first report on the phytotoxic activity of *Wedelia chinensis*. Our research indicated that *Wedelia chinensis* can be used for the biological control of weeds, which may help to develop organic farming.

**Author Contributions:** Conceptualization, K.H. and H.K.-N.; methodology, K.H., A.I., K.S., K.R.D., S.O., and H.K.-N.; software, K.H. and K.R.D.; validation, A.I., K.S., K.R.D., S.O., and H.K.-N.; formal analysis, K.H. and K.R.D.; investigation, K.H.; Resources, H.K.-N.; data curation, H.K.-N.; writing—original draft preparation, K.H.; writing—review and editing, H.K.-N.; visualization, K.H.; supervision, H.K.-N. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was funded by a MEXT scholarship, grant number MEXT-193490, from the government of Japan to carry out the research in Japan.

**Acknowledgments:** The authors are thankful to Dennis Murphy, The United Graduate School of Agricultural Sciences, Ehime University, Japan, for editing the English of the manuscript.

**Conflicts of Interest:** The authors declare no conflict of interest.
