I am of the opinion that rural funding (SFP, or SRDP etc.) should be sanctioned if landowners harbour these plants with no active management plan in place.
However it's very unfair if a riparian owner controls invasives but the upstream landowner doesn't bother.
I think the Don team are working their way downstream. A few years ago EnviroCentre, the company I work for, surveyed the CNPA don habitats and didn't find any.
Kemnay/Fetternear is bad for G.Hogweed. It's a serious issue. If it was mapped throughout the don catchment, it would be shocking and a bit embarrasing for some I think.
If people pay for a days fishing and they are constrained by hogweed, I think they are within their rights to request a refund, thus forcing riparian managers to make the economic decision to remove these plants.