Posted: 06/07/2017 at 11:58
Himalayan balsam ... originally introduced to the UK as a garden plant, but it has become naturalised and is a major pest in some areas ... particularly on river banks as the way it grown prevents the stabilisation of banks and allows erosion.
It is illegal to plant it in the wild in the UK.
The seeds are catapulted many feet through the air - in this way it spreads very quickly. A misguided neighbour once grew some and very soon the whole street had a problem.
Thankfully it's an annual, and the young plants are easily identified once you know what you're looking for, and they're easy to pull up while they're small.