I have some pretty mallow growing in a gravel bed. Easy what I don't want just pulls out. I made a mistake and let some grow in a flower bed, which I now want to remove. I cannot get rid of one. The hole I have dug is about 8 inches deep, but nowhere near the root. There were some green shoots which I left and spray and the root as well with Roundup. The green shoots have died. Will the whole root die as well. ? Thanks, Mrs Bouquet