"Certain characteristics determine which term is most accurate – or whether the weed in question might actually fit into multiple categories."
"Once a weed is classified as noxious, authorities can implement quarantines and take other actions to contain or destroy the weed and limit its spread. Examples: Purple loosestrife (Lythrum salicaria) Hydrilla (Hydrilla verticillata) Witchweed (Striga spp.)"
"Invasive weeds are not native to the ecosystem under consideration and cause or are likely to cause harm to human, animal or plant health, the economy or the environment."
Click over to the link at the top to read the rest and see the photos of all the weeds and their level of noxiousness.