Cattails growing in agricultural drainage ditches undergo frequent ditch bottom drying out periods during dry mid-summer periods. The cattails always seem to regrow text spring. You may see a decrease in the amount of new growth next spring but soon the patches will be thriving and expanding once again. If you really want kill the groupings you should use a good systemic herbicide such as Shore-Klear plus or Rodeo with a surfactant after flowering so it moves into the roots for killing action.
