The weed pictured here is common pokeweed (Phytolacca americana). 

Common pokeweed is a large, branched perennial plant that reproduces by seed and may regenerate from a large, underground taproot. Leaves are alternate, large, and smooth with slightly wavy margins. The leaf undersides may be tinted purple or red. Stems are erect, reddish, and also smooth. Flowers are white followed by purple to black berries in later summer or fall. Birds love to eat these ripe berries and thus spread common pokeweed seed around.