Allelopathic effects and composition of aqueous extracts from different parts of <i>Galinsoga parviflora</i> Cav. on <i>Medicago sativa</i> L. and <i> Avena sativa</i> L

(1) The inhibitory effects of aqueous extracts from different parts of <i>G. parviflora</i> on recipient plants were different, the root was the weakest, and the whole plants was the strongest, with the values of synthetical allelopathic effects (SAE) on <i>M. sativa</i> at the highest concentration being -0.12 and -0.40, respectively. (2) Compared with <i>A. sativa</i>, <i>M. sativa</i> was generally more susceptible to the extracts. (3) The differences in the content of CHDA or trehalose might be a reason why extracts from different parts of <i>G. parviflora</i> exhibited different allelopathic effects. (4) The herbicidal activity test of key allelopathic substances found that CHDA has a strong inhibitory effect on the germination of <i>D. sanguinalis</i> and almost does not affect <i>M. sativa</i> and <i>A. sativa</i>. Thus, this discovery not only revealed allelopathic effects and components in different parts of <i>G. parviflora</i>, but provided scientific evidence for weed control based on natural plant extracts in the future.