Boil some water and pour it on the leaves of the oxalis weed. Each time you see new oxalis developing, repeat this process.
Combine 2 tablespoons of baking soda with a little bit of dishwashing liquid and pour it around the oxalis. This is especially effective on a hot day, since the roots will absorb it faster. This will weaken the root system and destroy it if you continue the process on a regular basis.
Mix 1 ounce of dishwashing liquid with a gallon of vinegar. Pour this combination into a spray bottle and use it on the oxalis. The soap will help the vinegar adhere to the leaves and kill it. This is only a temporary solution, since it is not very effective against the roots or the bulbs that cause them to reproduce.