Ambrosia artemisiifolia is a wide spread weed of composite in Northeast China. This paper studied the allelopathic effect of A. artemisiifolia, so as to elucidate it's spreading mecha nism and to find some ways to control it. After a series of experiments, we found some inter esting results: 1. Volatile of this weed has some inhibit effects on seeds germination of soybean and maize, the length of maize root treaed by volatile was shorter than that by control. 2. The water extract of the upper-ground part sh...