I assume these are tree roots we're talking about?
There are organic herbicides that will kill specific varieties of trees but, it's not really my expertise. If you don't want to kill the tree(s), I don't know of another alternative either.
yes i don't mind killing the trees please tell me what to use
Sorry, I lost my internet connection.
I know vinegar will kill tree roots but, you might be able to simply remove all the bark to kill the tree depending on the specie. If the tree is hearty, cutting it down and grinding the stump might be your best bet. As far as killing the tree with an organic herbicide, consult your local nursery for something specie specific.