Japanese knotweed herbicide treatment
A herbicide treatment programme is the most cost-effective way to control Japanese knotweed — typically £1,000–£5,000 over 2–3 growing seasons. Professional-grade glyphosate is sprayed or stem-injected in late summer so the plant draws it into the rhizome. It controls rather than instantly removes the plant, and comes with an insurance-backed guarantee lenders accept.
How herbicide treatment works
A certified applicator treats the knotweed at the optimal time of year — usually late summer, when the plant is moving nutrients down into its root system. Depending on the site, herbicide is applied by targeted foliar spray or injected directly into each hollow stem to protect surrounding plants. Treatment repeats over 2–3 seasons with monitoring for regrowth.
Herbicide vs excavation
Herbicide is far cheaper and less disruptive than excavation, making it the usual choice for homeowners keeping their property. Excavation removes the plant immediately but costs 4–10× more — better when you're selling or building now. Both should carry an insurance-backed guarantee.
Herbicide vs excavation, compared › · All treatment methods ›
What to expect during the programme
A herbicide programme is planned around the plant's growth cycle. You'll be told when each visit is due, and there's little disruption to your garden between treatments.
- ✓Year 1: initial treatment(s) in the growing season, then dieback
- ✓Years 2–3: follow-up treatments as regrowth appears
- ✓Ongoing: monitoring visits to confirm control
- ✓Completion: sign-off and activation of the guarantee
Dead brown canes after treatment are normal and can be cut and left on site once fully dry — your specialist will advise on safe handling.
Your treatment programme, season by season
Herbicide control works with the plant’s natural cycle, so results build over two to three growing seasons plus a monitoring period.
- 1Survey & baseline — Year 1, spring
The surveyor records the extent of growth, maps the stand and sets the treatment schedule and guarantee terms.
- 2First treatments — Year 1, Jul–Oct
Professional glyphosate is applied by foliar spray or stem injection in late summer, when the plant draws chemical down into its rhizome.
- 3Growth checks — Year 2
Regrowth is monitored and re-treated at the right time; visible growth reduces markedly compared with year one.
- 4Reduced treatments — Years 2–3
Applications continue only as needed until the plant stops re-emerging above ground.
- 5Monitoring period — Years 3–5
Little or no growth remains; the site is monitored to confirm dormancy and satisfy the insurance-backed guarantee.
- 6Guarantee & sign-off
With treatment complete, your transferable IBG documents the work for lenders and future buyers.
