This is the first stem of Japanese knotweed I have seen this year. It’s a bit too early to start to treat it, but clearly it’s going to be a growing year after the mild winter we have just had!
You have to admit it is a lovely flower. Don’t worry its rarely spread in this country by pollen in the flowers. Its spread either through cutting down the stems and not disposing of it in a safe manner or digging up the roots and again not disposing of it in a safe manner.