Giant Hogweed is a dangerous plant and physical control of it is generally unsuccessful. Therefore, the best way in which to deal with it is through a herbicide treatment programme. Giant Hogweed requires treatment in the early growing season (April-May) and generally for a minimum of three years due to its seeds remaining viable in soil for this period.
Chemical treatment only affects germinated plants and not the seeds which are present within soil. This means continual treatment before seeding is required to achieve eradication and if a single year of treatment does not take place you may be taken back to step one with new seeds germinating in following years.
Treatment on riverbanks is generally unsuccessful due to seeds often being washed down from further upstream. Therefore, a river system wide Giant Hogweed control plan should be implemented to achieve eradication or annual monitoring visits made to the problem infestation to keep it under control.