I've used a vinegar based weed killer. Not a home mix, a proper horticultural strength product. For a large area that is already under some control it works ver

I've used a vinegar based weed killer. Not a home mix, a proper horticultural strength product. For a large area that is already under some control it works very well as it'll kill all the seedlings outright. For larger plants it varies in effectiveness. If you've already sprayed with roundup you could switch to control with horticultural vinegar. On the safety front, it would burn your skin if left on for a few minutes. Other than that I've found no information that it's bad, it is really just very strong apple cider vinegar.