I got lots of weeds of this kind in my back yard. Please see attached
pictures. The roots are white.

http://img135.imageshack.us/img135/1962/weed1fg4.jpg
http://img71.imageshack.us/img71/4935/weed2va9.jpg

It does look like Dallisgrass. But I'm in mid-west Canada. According to some
books, dallisgrass can only be found in southern US.

Appreciate any advice on what it is and how to combat the annoying stuff.

John