Allelopathic effect of Cirsium arvense and Asclepias syriaca

Allelopathic effect of two serious perennial weeds (Canada thistle and Common milkweed) was studied in bioassay experiments. Water extracts were made from different plant parts (fresh leaves, stems and roots) of Cirsium arvense and Asclepias syriaca, using 25 g fresh plant part x 100 ml(-1) distilled water as a stock solution. Stock solution was applied in 2-, 5 - and 10- fold dilution in order to determine their effects on the radicle length and germination of test species (garden cress, wheat, corn and sunflower). Inhibitory effects seemed to be greatly depending on donor and recipient species, plant parts and the concentration of the extracts.