The plant is Pokeweed (Phytolacca americana). It is a is a nonwoody (herbaceous) perennial that grows 3 to 10 feet (0.9 to 3 m) tall. The large, fleshy taproot can grow 1 foot (30 cm) long and 4 inches (10 cm) thick in older plants. It is native to North America. All mature parts of the plant are toxic to humans. Mature pokeweed contains a poisonous chemical compound called phytolaccatoxin.
Wild birds find the large juicy berries of pokeweed a good source of food.
Pokeweed can be destroyed by being chopped off below the root crown. Pokeweed is susceptible to many of the herbicides commonly used to control broadleaved weeds.
Here's a link to more detailed information about pokeweed: