I'd be willing to bet that the problem was cold soil not herbicides.
Try your test again using a propagating mat or heating cable or even
the top of your cable box.
The American Community Gardening Association listserve is only one of ACGA's services to community gardeners. To learn more about the ACGA and to find out how to join, please go to http://www.communitygarden.org
To post an e-mail to the list: firstname.lastname@example.org