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Is Japanese knotweed illegal in Montana?
Sources (6)
- ARM 4.5.206 Priority 1A (LII) – Cornell Law School Legal Information Institute
- ARM 4.5.207 Priority 1B (LII) – Cornell Law School Legal Information Institute
- ARM 4.5.208 Priority 2A (LII) – Cornell Law School Legal Information Institute
- ARM 4.5.209 Priority 2B (LII) – Cornell Law School Legal Information Institute
- ARM 4.5.210 Priority 3 (LII) – Cornell Law School Legal Information Institute
- Montana Dept. of Agriculture — noxious weeds – Montana Department of Agriculture
Also called: Reynoutria (Fallopia) japonica. Last checked against official sources: 2026-10-14.
Federal noxious weed list (7 CFR 360.200): Japanese knotweed is not listed.
What Montana's official list says
| List / legal category | Listed as | List note | What it means |
|---|---|---|---|
| Priority 1B noxious weed (ARM 4.5.207), control list — eradicate or contain — not a sale ban | Reynoutria japonica (syn. Fallopia japonica, Polygonum cuspidatum) | Japanese knotweed | Not a sale ban — control-only list |
Effective dates
- The official list entry does not state a separate effective date for this species. See the linked law for when the listing took effect.
Already have it in your yard?
Control lists can require landowners or agencies to control or eradicate the plant. The list says it is not a sale ban, but control duties may apply to you as a landowner.
Native alternatives for Montana
- American elderberry (Sambucus canadensis)
- Red osier dogwood (Cornus sericea)
Each is recorded as native to Montana in the USDA NRCS PLANTS Database state distribution (retrieved 2026-10-14). Check size, sun and soil fit for your site with your local Extension office.
More native swaps with hardiness, light and size →
Japanese knotweed in other states
Alabama California Colorado Connecticut Delaware Idaho Illinois Indiana Kentucky Maine Massachusetts Michigan Minnesota Nebraska New Hampshire New York Ohio Oregon Pennsylvania Utah Vermont Virginia Washington West Virginia Wisconsin
See every plant on Montana's invasive & noxious plant lists, or check any plant.
Not legal advice. PlantLegit summarizes official lists and links the source. Laws change, local (county/city) rules may add restrictions, and the official text controls. "What it means" is our plain-English label; read the exact list wording. Confirm with the agency before buying, selling or removing plants. Full disclaimer.