Trial finds woolly warriors effective against giant hogweed

Trial finds woolly warriors effective against giant hogweed - NatureScot

A four-year trial has found that sheep grazing effectively reduces the spread of giant hogweed, a highly invasive and harmful non-native plant.

A flock of woolly warriors were introduced by the Scottish Invasive Species Initiative into woodland alongside the River Deveron to munch their way through invasive giant hogweed plants. The Initiative is led by NatureScot and funded by the National Lottery Heritage Fund, NatureScot and by in-kind support from project partners and volunteers.

The sheep were introduced into the strip of woodland along the river beyond the Macduff distillery as part of a hogweed grazing trial in 2019. Giant hogweed is one of the most notorious invasive non-native species in the UK. Not only is it highly invasive and easily spread – each seed head can produce 20-50,000 seeds, all potentially viable for up to 10 years – but it also contains a phytotoxic sap within its leaves and stems which can cause severe skin burns to humans.

An infested site must be treated consistently for many years (sometimes 10 or more) to fully exhaust the seedbank. Infested sites are normally treated by spraying pesticides onto the leaves of the plants and by cutting flowering heads to prevent further seed production. Over time, this will kill off the infestation and deplete the seedbank in the soil. However, this can be time consuming, costly and physically challenging – especially in difficult terrain.

However, once familiar with the plant, sheep will readily and even preferentially graze on giant hogweed with no adverse effects from the sap. Over time, grazing depletes the resources stored in the plant’s taproot and eventually kills it off.