Effect of Canada Thistle (Cirsium arvense) Residue on Growth of Some Crops

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Abstract
Field and greenhouse experiments were established to determine the phytotoxicity of Canada thistle [Cirsium arvense (L.) Scop.] residue on crop growth. Field examination of infestations showed that as Canada thistle shoots increased in an area, the number of kochia [Kochia scoparia (L.) Schrad.], marshelder (Iva xanthifolia Nutt.) and foxtail barley (Hordeum jubatum L.) plants decreased. Conversely, as Canada thistle shoots decreased, the aforementioned annual and perennial plants increased. In greenhouse studies, roots and shoots of Canada thistle that were mixed with soil reduced the growth of sugarbeet (Beta vulgaris L. ‘Mono Hy D2’), wheat (Triticum aestivum L. ‘Centurk’), alfalfa (Medicago sativa L. ‘Dawson’), and Canada thistle seedlings. Corn (Zea mays L. ‘Jacques No. 1004’) and dry edible beans (Phaseolus vulgaris L. ‘Great Northern No. 59’) grown in soil treated with Canada thistle residue were affected to a lesser extent. When Canada thistle residue was mixed with soil, crop growth was inversely proportional to the amount of Canada thistle residue added to the soil. Both roots and shoots of Canada thistle were toxic to crops when mixed with the soil. The effects of Canada thistle residue on crop growth lasted for about 60 days. Neither autoclaving residue and soil nor fertilization of soil had any effect on residue toxicity. Canada thistle leaf leachate inhibited the growth of sugarbeets watered daily with the leachate.