This is called Japanese knotweed (Reynoutria japonica). Unfortunately, it is a non-native, invasive perennial plant that can be very challenging to control. The key is to remove the plants as soon as they are observed -- and remove/kill all of the root system. Consistent and repeated removal by hand should include cutting the canes and digging up the roots. Allow the cuttings to dry out in the sun before disposal. Do not compost them, as they can continue to regenerate and spread by any live pieces of the root system. A systemic herbicide application (using glyphosate) can kill Japanese knotweed, but it may take 3-5 years to eradicate it completely. A systemic herbicide, applied to the foliage, will move inside of the plant down into the root system to kill it. Penn State Extension has a calendar that shows the optimal times for an herbicide application in late summer (July-September). Read and follow the product label when you use an herbicide. 

Here is additional information about this plant, how it spreads, and how to control it.

Christa