I guees it was not brown originally, can you identify it?
Likely goldenrod (Solidago species) fully mature, gone to seed and turning brown as it dries out. Solidago is another of the aster/sumac temperate autumn crowd. Confirm this by examining the base of the dry stalk, which may show small green leaves which are the suckers of this perennial plant ready to grow for the next season. Grab one of the stronger stems towards the base with both hands and give it a sharp tug. This will bring up a small section of root with young plants attached.