Rick I would agree with you that all chemical should be used with caution. But you are throwing out a lot of negative information about vinegar, using a words like, probably, offhand expect , thinking that. These are not words that give me a lot of confidence in what you are saying. You offer no evidence other than what you THINK. I have been reading about vinegar as a herbicide and the only negatives I have found so far are, that may not be effective on some weeds, it is only a contact killer and does not get the roots and it can be physically hazardous ( burn the skin) in high in the higher concentration (20%), which is why all chemicals should be handle safely. The links that I gave terrafirma recommend no more than 10%. You said "I don't think any soil fungus would tolerate pH 4". Where is the evidence that vinegar would have this effect.
If found this research by Swedish Agricultural University: "Addition of 24 % vinegar to a peat soil decreased the pH of the soil from 7.3 to 5.6. However, after 48 hours the pH values
of the soil returned to 7.0-7.5"
That is an extreme concentration, far in excess of the recommended 10%.
