"These weeds don't require animals [to disperse]. They're windblown, they're blowing out onto island forests where humans can't see it happening. They crush a tree. They're not selective. They keep growing and getting heavier, trees suffocate."
Mr Henty has identified 1600 sites already and been out every weekend removing them.
"Last year we had 1000 [sites logged]; we visited 200. We've seen 1600 now in total and visited a good many of those.
"Typically it's me visiting in a spare chunk of time - eg summer days, longer evenings. Then I tried getting a vanload of kids coming out. We'd go to an infestation side and pull them out."
Mr Henty says everyone should take responsibility for the problem.
"Everyone should adopt a weed. That would work.There are certainly other people out there like me who have a pet problem, like the guy who noticed rubbish around the coastlines.
"The council can't enforce mothplant removal from a citizen's property, but they're trying to promote awareness. I would assume they're happy with the work we're doing."