Birds will eat the 100 seeds on each flower stalk and spread them around to grow yet more plants.
Wild ginger is semitropical, and the warmth expected from climate change will speed its spread.
It can be controlled by spraying, cutting and spraying, or by manual removal. The best method depends on the situation and Mr Gallagher is willing to give advice or help.
He's got a team to work with, including the "Ginja Ninja", a ginger eradication specialist.
Horizons Regional Council has a prize - a 16-litre garden sprayer - for the person who finds the biggest infestation of wild ginger in Wanganui.
The ginger campaign will run until the end of November, and Mr Gallagher is happy to advise on other problem weeds as well.
He said his previous woolly nightshade campaigns had opened the eyes of people and got them talking.
"They're starting to think weeds, and that Horizons is there to help them."
Mr Gallagher can be contacted on freephone 0508 800 800.