If you are talking about the weed that is also called horse tail, then my sympathies as this weed has been around since pre historic times and is difficult to eradicate. I removed a patch that come in with some mulch by cutting it to the ground every few weeks with a string trimmer. Keeping the tops cut off will starve out the roots. Pulling it will only stimulate the roots to send up new shoots and herbicides are not very effective because of the texture of the foliage. Just keep cutting off the tops and you will eventually be victorious in this weed war. Keep growing - but not horsetail, Marianne Binetti