I started out by moving the sunroots to a different part of my garden every year. Now I grow them in a perennial bed (from which they invariably escape, and I have never reclaimed any space where they grew in the past. The only way I have eliminated them involved denying irrigation to the field for an entire growing season (in the desert).
I grow them in one permanent row now, about 6 inches wide, and I maintain a 6 foot wide tilled space on either side of the row. During the growing season, I zig-zag the rototiller through the row, and I pull by hand, so that I maintain about one major plant every 3 feet in the row.
For making seeds, I chop the plants off at about waist height, early in the growing season, so that they send out lots of side shoots.
