If you can't wait the two years, I'd say 6' is way too close.* If you have a heavy rain the entire area will be soaked and water travels through the soil.* If you can find a variety you like that is resistant to the wilt, you will need to find another area.
You can do a google with terms such as:
blackberry + resistant + verticillium wilt
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.