Current needs - Five acres ready to plant seashore mallow. Given the time and not knowing the field conditions tilling would seem to be the best option, but local knowledge of the setting could alter ...
To make sure it doesn’t return you have to interrupt the seed-to-flowering-plant cycle at least for a couple of years and fill the voids with something competitive.
At first glance, musk mallow (Malva moschata) seems like a highly attractive plant. Its blooms are a pretty pink, and crushing its foliage leaves your fingers covered in a pleasant, musky fragrance.