Covering kills invasive keltalammikki in Aurajoki River

A trial to control the invasive keltalammikki plant in the Aurajoki River near Turku has produced promising results, with plants dying beneath coverings, Yle reports.

The coverings were placed over five areas near Vanhalinna in Lieto to block light and prevent the plant from growing and spreading. When they were removed on Tuesday after about three months, no plants were found underneath.

It remains unclear whether the plant died all the way to its roots or whether only this year’s growth was destroyed. The project team visited Sweden to study the method, where covering the plant for one growing season, or sometimes less, has been sufficient.

The Aurajoki River has around 50,000 square metres of keltalammikki, while coverings were installed over about 500 square metres this summer. The trial will continue next summer, when the coverings will be placed further upstream.

The goal is to eliminate the plant from upstream areas and drive its spread towards the sea. The method may be expanded in future years if additional funding is secured.

The trial also showed that the coverings appear to work in flowing water. The project team had previously observed the method in still water, such as lakes.

Keltalammikki forms dense mats of yellow flowers on the surface of waterways and suppresses native vegetation. The plant was introduced to Finland as an ornamental plant and was first observed at Lake Littoinen in 2012.