Western ragweed (Ambrosia psilostachya DC.) top growth and rhizome extracts were inhibitory to germination and growth of seedling shoots and roots of test plants in almost all cases. Germination of all plants tested was reduced an average of 19.5% by the ragweed extracts. Shoot and root growth of plants tested was reduced an average of 56.8% by the ragweed extracts. The combined effects of germination plus growth reductions resulted in the tested plants producing only 34.8% in the extracts compared to production in distilled water.