I’ve found this to not work too well on oxallis because the surface of the leaves are pretty hydrophobic. I have pulled the foliage and then painted the top of the exposed root if I’m not able to pull the carrot shaped root.
I had a huge oxallis issue, but it was mainly because I was lazy. This year I wanted to attack it head on. I started by buying a pair of tweezers, pulling each affected pot (aka all the pots) into my workshop, and pulling at each root one at a time with my tweezers. I called the main carrot root the “mother root”. You kinda have to grab the top of the root and wiggle back and forth. Most of the time it’ll eventually come out and then surprise you with how deep it went.
Oxallis will send runners that will eventually become mother roots if the they’re allowed to remain in the pot. Luckily those are fairly easy to get rid of. The mother roots are not. Sometimes I would not be able to pull the mother out at which point I would dab the top of it with a vinegar soaked q-tip.
I did two pots a day which surprisingly didn’t take too long. After that you kinda just go into maintenance mode. Everyday while watering just pluck the leaves as you see them while trying to pull the mother root. Eventually the top of the mother root will get fairly swollen since it’s had to keep creating new foliage. That makes it easier to either pull out by hand or with tweezers.
The main thing is that you DO NOT want to let them go to seed. When pulling the weeds I also just lay it on the bench to let it dry out. If you just toss it on the ground you’ll end up with weeds all around your bench and then eventually in other parts of the garden as it sends out seeds.
It really only took me one spring to get things back to manageable. Whenever it would rain I would walk the garden to weed since I didn’t have to water. If I was watering I’d just pull the occasional weed here and there.
Stay diligent and good luck!