Howard Downer warned that building professionals, including landscapers and designers, often failed to grasp how to handle the invasive weed.
"There are still landscapers out there who aren't fully aware of the issues, not necessarily through ignorance but a lack of knowledge," he explained.
Downer, managing director of TCM, has worked on Japanese knotweed for 20 years and is helping Olympic officials tackle the problem in London.
He said he was "very surprised" a mortgage lender recently refused a loan to a homeowner after a surveyor found knotweed in a flower bed (HW, 11 June).
"I feel these things are driven by scare stories picked up on the internet. Lack of knowledge and education can be bigger problems than the weed itself. A little bit of knowledge can be a dangerous thing," he concluded.
Downer said he aimed to run his courses starting from this autumn and wanted industry groups to work together on "more user-friendly guidance on what it is, what it can do and what can be done".