Japanese knotweed takes invasive weeds to a new level with its ability to actually break concrete if allowed to grow in cracks and joints. It is extremely invasive and can cover disturbed ground very quickly. Knotweed is spreading rapidly, especially in the eastern U.S. The risk for contractors is that with its addition to the list of invasive weeds that must be controlled, it could cost you a lot of money to keep it in check on a jobsite. The Canadian Journal of Commerce reports that knotweed control added 70 million pounds to the costs for the London Olympics and it is being found even in Vancouver.