I would check into digging it up from ditches, if it grows there. Usually, whoever maintains the road shoulders (city, county, state) will clean out the ditches periodically and they make no effort to save any vegetation. And if they routinely mow (or spray) the shoulder between the roadbed and ditch, that also seems like 'fair game' to me. Even though this seems practical to me, it may still be illegal. Regulations are often not based on common sense.