keep up the good work. I can assure you that pulling it up does work. I was at the same stage as you few years ago. You start getting a real hawk eye for spotting HB. Go back in two weeks and check for flowers or wander down the opposite bank of even wade in the water. Next year there will only be a few plants and the year after that none.
I still have to patrol because I have seed coming downstream. I blame the logging companies who move seeds around on their wheels and bring them to the headwaters. SEPA and the council do nothing.