I tested some herbicides against oxalis. Quicksilver was best followed by T-Zone, Surge and Speedzone. And untreated control. All products worked well, as the oxalis is almost invisible, due to the almost complete collapse of the plant. Perhaps conditions were unusual due to the oxalis arising and blooming in late summer after a dry dormancy period. Oxalis normally blooms in late spring. I think it is normally more difficult to kill. I applied about a tenth of an ounce per sqft, (about .78 gals per thousand sqft).