Changing of amounts of allelochemicals in Italian cocklebur (Xanthium italicum Mor.) during the growing season.

The results of an experiment that evaluated the effects of rainfall, and the phenology and density of cockleburs (X. italicum) on the allelopathic effect of cocklebur extracts on cress (Lepidium sativum) are presented. The amounts of 4 allelochemicals (chlorogenic acid, pcoumaric acid, coumarin and trans-cinnamic acid) were measured in the roots and shoots of cocklebur. The amounts of chemicals increased up to 4- to 30-fold relative to the minimum concentrations in some samples.