Japanese Knotweed: A Problem in Japan Too

It’s Invasive at Home as Well

Contrary to the myth that Japanese knotweed (Fallopia japonica) is only a problem in the UK, it is also invasive and damaging in its native Japan.

• In Japan, it colonizes riverbanks, roadsides, and disturbed slopes, outcompeting native vegetation.
• Its aggressive rhizomes damage foundations, pavements, and flood defenses there too.
• Japanese authorities actively manage it; it’s listed as a "Priority Invasive Alien Species."

The difference: in Japan, it has natural enemies (insects, fungi) that provide some control. In the UK, lacking these, it spreads unchecked—making it more problematic, not exclusively so.