The effects of leaf extracts of crack willow (Salix fragilis) on the growth of Japanese knotweed (Fallopia japonica)

Japanese knotweed (Fallopia japonica) is one of the most invasive of species in Europe, and can substantially reduce local native biodiversity. In the present study, the allelopathic potential of crack willow (Salix fragilis) on growth of Japanese knotweed was investigated.Aqueous extracts of 0.1% and 1% (w/v) were prepared from liophilised willow leaves and used for watering of young knotweed plants. Their growth was monitored for 196 days. Shoot height and leaf number were not affected but the mass of leaves and especially roots was reduced (up to 32%). At the end of experiment, biochemical characteristics related to physiological state (photochemical efficiency of PSII, protein content, enzyme activity of guaiacol peroxidase, lipid peroxidation) were measured. Mostly, they were at control levels, but the activity of guaiacol peroxidase and lipid peroxidation in roots increased. The extracts of crack willow showed moderate inhibitory effect on roots of treated knotweeds while the growth of shoots was unaffected. Given the root reduction described here, further studies with willow extracts and field studies with crack willow and Japanese knotweed plants would be reasonable.