In order to determine the allelopatic effects of Russian knapweed on wild barley, a bioassay study was conducted. The experiment was based on completely randomized design, with 4 replications. The studied factors were Russian knapweed parts (shoot or root), and concentration of plant extracts (0, 15, 25,30,35,40,45,50,75 and 100 percent). Results showed that the allelopatic effects of Russian knapweed on wild barley were very significant. Plumule and radicle length genus length, percentage and germination rate were significantly reduced. This reduction was higher in shoot compared to roots of Russian knapweed

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