I don't see it being Horsetail, looks too smooth, but some kind of rush it certainly is. I generally don't see a problem with rushes in general but that can vary from place to place. Either way I wouldn't be overly concerned.
Check to see if the stem in segmented, as horse's tail is segmented where other rushes are a solid tube, solid as in lacking segments.
BTW, the Brazos River Bottom is lousy with Horse's tail.
