Allelopathic plants. 1. Canada thistle [Cirsium arvense (L.) Scop]

The genus Cirsium has more than 60 spp., all species are weeds and distribu ted in temperature and subtropical regions of the world. Cirsium arvense is most abnoxious weed and reduces productivity of crops, pastures and orchar ds. it grows in colonies and kills the original plants through allelopathic interactions. It propagates through roots and one plant can spread in 2 m( 2) area by horizontal roots, it is allelopathic weed and inhibits the growt h of associated crops due to release of phenolic compounds. In bioassays, p ot culture and field studies, the biomass or its extracts inhibited germina tion and seedling growth of crops. The phytotoxicity of soil incorporated b iomass persisted in soil upto 9 weeks.