Question
I live in NW WA. My sister recently dug up a root from a viney weed in her yard. The single root grew down three feet then turned into the size of a watermelon.  She dug this root out of the ground, literally one root, the size and shape of a watermelon.  the plant is viney with small white flowers and green seed pods. What kind of weed could this be? while getting rid of it, do we have to dig out every root the size of a watermelon? Thank you for your time.

Answer
I should 'reject' this question as 'outside my area of expertise', but it's important to (a) post this for the world, in the event that someone else recognizes it, and (b) let you know that this kind of flora ought to be i.d.'d in person by your local Cooperative Extension Service, which for you is at Washington State University:

http://ext.wsu.edu/

Satellite offices are located in each County.  Find yours here:

http://mastergardener.wsu.edu/mgoc/mgoc.html

This is right up their alley.  Let me know what you find out.  Thanks for writing.

L.I.G.