Shoreline Defense works on emergent aquatic weeds, including cattails and phragmites, and other shoreline vegetation. Pond Logic Shoreline Defense kills weeds down to their roots. For best results, apply Shoreline Defense while the chosen weed is in its active growing stage. For cattails, it is best to apply during late summer to early fall when stalk is 12-18" high. This herbicide does not have water use restrictions.