Welcome to the forums wlkonkin. You have my sympathy. This attractive flower is a real pest,an invasive plant from the Himalayas. Impatiens glandulifera. Himalayan balsam. http://www.google.co.uk/search?q=im...&source=og&sa=N&hl=en&tab=wi&biw=1270&bih=501 The ripe seeds just explode when touched. Shooting seeds many feet away from the parent plant.
Just been added to the BC Provincial Noxious Weed list (July 2011). This designation means that a property owner who has one of these species on their property has a duty to control (i.e. remove/kill etc) it. I wouldn't worry too much if you can't get rid of it all, these species are all over...you won't go to jail :) Impatiens tends to follow watercourses to spread. Likes moist part shady areas. As Michael F. said, pull, weedwhack, clip it prior to seed pods maturing. Don't let it's pretty flowers fool you...this is a nastily agressive plant in BC.
