Scotch broom is noxious in Pacific Northwest
Be on the lookout for prickly Paterson's Curse in wildflower seed mixes.
Gorgeous yellow iris Is ecological threat to PNW wetlands
Oregon is the first state to list invasive non-native grass called false brome as a noxious weed.
Butterfly bush, or Buddleia, can be a very aggressive non-native plant that, in certain situations, can overtake native vegetation. Take care to cut blossoms off in the fall.
Browning or dieback is usually caused by weather-related stress, sometimes in combination with pests and diseases.