MB Estate Limited were served with a community protection notice back in May 2017 following complaints from seven properties neighbouring the house on Ash Road in Horfield.
After no attempt was made to comply with the notice, Bristol City Council took the decision to prosecute the owner of the property.
The company, who did not attend the hearing or sentencing, were fined £18,000 plus costs, in their absence, at Bristol Magistrates Court.
The court has also issued an order requiring MB Estates to remedy the problem. This includes securing a plan from a specialist company detailing how the issue will be resolved. This must be done within 28 days.
Councillor Kye Dudd, Cabinet Member with responsibility for regulatory services, said: “It is unfortunate that the council needed to resort to formal action, but we hope that this sends a message that appropriate action will be taken, when necessary, to protect the public.
“Knotweed has the potential to cause significant nuisance to property owners, causing structural damage as well as anxiety over the effect on property prices and the ability to secure a mortgage.”
It is thought that this is one of the first prosecutions nationally of Japanese Knotweed using the Anti-Social Behaviour, Crime and Policing Act 2014.