Giant hogweed (Heracleum mantegazzianum) was introduced into the UK in the 1800’s as an ornamental garden plant. However it has now become naturalised in many river catchments across Scotland. On the River Spey it is known to be present in the lower river from Boat O’Brig downstream. The Mulben Burn is one known source of the infestation on the Spey as it is reputed to have spread from a garden on the banks of the upper Mulben Burn.
As with most invasive species Giant hogweed is capable of out-competing and dominating native plant species to the detriment of native biodiversity. Giant hogweed also presents a serious threat to human health as contact with its sap can result in blistering of the skin. The sap reacts to sunlight and blistering of the skin can recur over a long period on exposure to the sun.
Giant hogweed is a monocarpic plant; that is they flower once then die. It can take up to four years for a plant to become mature. Individual plants can grow to over 12’ high and in the final year of their life they produce the characteristic large white flower head which can result in up to 50,000 seeds. The seeds can remain viable for up to 15 years so persistence is required in any control program.
Giant hogweed plants can be controlled using the appropriate chemical treatment. Control is best undertaken on immature plants in spring and early summer when the volume of chemical required the plant will be less.
Further details about Giant hogweed can be found on the Invasive Species Scotland website.