Japanese Knotweed Control (JKC) has completed a three-year blitz of the invasive plant to virtually eradicate an infestation from college grounds.
The company said the weed threatened the new campus at Nelson & Colne College in Lancashire. Architects identified the plant in 2008 while working on a £20m new-build and refurbishment job.
Knotweed, first spotted on a riverbank beside the development on a former mill site, spread to footpaths and driveways and triggered fears that the plant could undermine building structures if left untreated.
Cheshire-based JKC treated the weeds by injecting glyphosate herbicide into plant stems and digging trenches to check on the root structure and the likelihood of spreading.
"Knotweed is very prevalent on brownfield sites by railways and waterways because it has very dense root structure and the Victorians used it to stabilise embankments," said joint managing director Richard Podmore.
"It soon became apparent this site had a massive infestation, but the three-year programme achieved an eradication rate in excess of 90 per cent. This is very high given the scale of infestation on surrounding riverbanks.
"Ongoing maintenance will ensure any potential regrowth is managed. Injecting herbicide directly into the plant stem is widely recognised as achieving maximum control and is considered ecologically sound."
"Japanese Knotweed Control was mindful of the need to uphold our strong green credentials and complete the treatment without adverse environmental impact on vegetation and wildlife. Regular progress reports keep us updated on schedules and results."
John Ellis, facilities manager, Nelson & Colne College