Phytotoxicity of velvetleaf (Abutilon theophrasti Medik.), common ragweed (Ambrosia artemisiifolia L.) and common cocklebur (Xanthium strumarium L.) to lettuce and tomato

We studied the main phenolic components of velvetleaf (Abutilon theophrasti), common ragweed (Ambrosia artemisiifolia) and common cocklebur (Xanthium strumarium) aqueous extracts and evaluated their phytotoxicity to germinating seeds and seedling growth of lettuce and tomato. A total of 13 phenolic compounds were identified in aqueous extracts. The highest total phenolic content was found in velvetleaf leaves, followed by common ragweed leaves and common cocklebur stems. Caffeoyl quinic acids were the most abundant phenolics in these three weeds, while common ragweed and velvetleaf leaves were also rich in p-coumaric acid and rutin, respectively. Other phenolic compounds were present in moderate quantities in the stems and leaves of the tested weeds. The weed extracts at 50 % concentration or higher significantly inhibited the seed germination and early seedling growth of lettuce and tomato. The leaf aqueous extracts were more phytotoxic to lettuce and tomato than stem aqueous extracts. The leaf aqueous extract of common ragweed had the strongest inhibitory effects on lettuce, while the leaf aqueous extract of velvetleaf was most inhibitory to tomato. The aqueous extracts of common cocklebur were less inhibitory to lettuce and tomato.