Using high strength herbicide can be counter productive. You have to look at the way herbicide works. The idea is for the herbicide to be taken in and distributed throughout the plant. This is best achieved during maximum growth in a healthy plant. The slower reacting nature of diluted poisons allows transfer without immediately killing the plant tissue. As the poison spreads through the plant it slowly makes it sicken and then eventually die wherever the poison has reached. Concentrated poisons will kill the tissue they come in contact with thus blocking further absorbtion Those parts of the plant die and the rest of the plant will resprout from its base that was left untouched. Plants with different types of metabolism react differently to different types of poison. Glyphosate ("Round-up" amongst numerous other brand names) is one of the most all-round herbicides, which is why it's used so much. But there are plants that don't get the same adverse effects. They need something else to knock them out. When it comes to vinegar, I haven't seen anything about how effective or broad ranging it is. I don't know if it has the same problem of becoming less effective in higher concentrations. But it's worth experimenting with to see what it will knock out. If it's not more 'environmentally friendly' than glyphosate, then at least it's a hell of a lot cheaper.
