Effect of phenolic compounds on the germination of six weeds species

Low molecular weight phenolic compounds have been identified in fresh leave s and in soils in which leaves of five varieties of Capsicum annuum L. were decomposing. Six phenolic compounds were tested in laboratory bioassays fo r their allelopathic effects on germination and seedling growth of six weed s. Ferulic acid, gallic acid, p-coumaric acid, p-hydroxybenzoic acid, vanil lic acid, and p-vanillin were bioassayed in concentrations of 10, 1, 0.1, a nd 0.01 mM. Equimolar mixtures containing all these phenolics were prepared at the final total concentration of 10, 1, 0.1, and 0.01 mM to test for po ssible interactive effects. Chenopodium album L., Plantago lanceolata L., A maranthus retroflexus L., Solanum nigrum L., Cirsium sp. and Rumex crispus L. were the selected target weeds. The highest concentration of the compoun ds inhibited the germination of all these weeds, but lower concentrations h ad no effect or were stimulatory. However, effects varied with the weed spe cies, the concentration of the compound tested and the compound itself. In assays with the mixture of phenolics we found evidence of some additive eff ects.