Misleading information about Japanese knotweed may be making private gardeners break the law, say researchers.
The poor advice on websites and provided by some councils could also be causing needless worry and expense, a study has found.
Japanese knotweed was brought to the UK as an ornamental addition to gardens and parks in the mid 1800s but has become a major menace.
Controlling the destructive weed, that can grow through brickwork and concrete, is estimated to cost £165 million a year in the UK.
Mortgage lenders have also been known to refuse loans for the purchase of homes blighted by Japanese knotweed.
It is a legal offence to plant or cause the weed to spread in the wild, and householders are required to dispose of it correctly.
Scientists from the University of Exeter who looked at knotweed guidance from a range of internet sources found that it varied greatly and was sometimes “contradictory and potentially misleading”.
While some councils, such as Devon and Cornwall, provided valuable and accurate information, others had issued conflicting online advice that could lead to “potentially unlawful” decisions.
Dr Beth Robinson, from the University of Exeter’s Environment and Sustainability Institute, said: “This does raise concern that if those responsible for domestic gardens consult only the website of their local government authority, the quality and clarity of the information received could vary geographically.
“It is important to provide clear advice about waste disposal of Japanese knotweed, as it can regrow from small fragments of rhizome and incorrect disposal of waste material can result in further spread of this plant.
“We recommend that local and national authorities collaborate and work towards disseminating more consistent messages.”
The study found that weed eradication companies tended to focus on the socio-economic effects of Japanese knotweed while the media often sensationalised the problem.
The plant should be dealt with on a case-by-case basis, said the authors writing in the journal Applied Ecology.
While professionals may sometimes have to be called in, small-scale appearances of Japanese knotweed in domestic gardens may not require expert treatment, they added.