Reply #5: here's one source, looking for more [View All]

[Muttocracy]

Usually household vinegar = 5% acetic acid in water solution.

"Although acetic acid may burn off the tops of Canada thistle and other perennials, it does not control the root system responsible for regeneration of plants. Furthermore, acetic acid may not control larger weeds, as indicated by a recent demonstration at the Nashua Research Farm.

Directed applications to weeds (thereby keeping the vinegar away from the crop plant) are necessary to use acetic acid in crop fields. Acetic acid concentrations from 10 to 20 percent controlled 80 to 100 percent of the smaller weeds, as reported in the USDA release. Typical concentrations of acetic acid in most commercially available vinegars are 5 percent and were reported to provided variable control of small weeds."

http://www.ipm.iastate.edu/ipm/icm/2002/7-15-2002/vinegar.html

(article has lots on legal issue of definition of a pesticide, so I just copied the most relevant part)