Covering trial targets invasive yellow floating-heart in Aurajoki

The Aurajoki Foundation is testing covers to control the invasive yellow floating-heart in the Aurajoki River, where the plant has spread across an estimated 50,000 to 60,000 square metres, Yle reports.

Covers have been installed at five locations in the river near the Turku region. The method is the foundation’s latest attempt to stop the plant, following trials with mechanical mowing.

“When the covers completely cover the plant, nothing grows. If there is a gap between the cover and the frame, plants push through. The cover blocks sunlight, and the plant dies underneath it,” project coordinator Sampo Ahlholm said.

The plant is displacing Finnish wild plants and restricting recreational use of waterways. In the Aurajoki, it is taking space from yellow water lilies.

The foundation’s research project will run for two years and continue next summer.

Swedish method adapted for flowing water

The covering method was developed using Sweden as a model. However, it has not been used there in flowing waters, so the Aurajoki Foundation is developing covers suitable for rivers.

“In Sweden, covering is an industrial operation. They have had to cover enormous areas. There is yellow floating-heart as far as the eye can see,” Ahlholm said.

In the Aurajoki, volunteers help monitor the covers during canoeing trips and report whether they have remained in place.

Rapid spread worries researcher

Miia Jauni, a senior researcher at the Natural Resources Institute Finland, is concerned about the plant’s rapid spread and the risk that it could expand across a large area of southern Finland.

The perennial plant can spread through both seeds and fragments. Its seeds and pieces may be carried by water currents, and waterfowl may also spread it.

Some fragments have spread during mowing. Jauni said covering could be an effective way to eradicate the plant, noting that the method has been tested successfully in Sweden.

The species was introduced to Finland as an ornamental plant and was first observed at Lake Littoinen in 2012, according to the Finnish Biodiversity Information Facility. It has also been recorded in Satakunta, Tampere and Lappeenranta, in addition to the Southwest Finland region.

Experts urge removal from garden ponds

Jauni urged people to remove yellow floating-heart from garden ponds and prevent it from spreading elsewhere.

There is no specific legal obligation to do so because the plant is not officially included on Finland’s national invasive species list. In Sweden, it is already on the country’s national invasive species list.

“It is worth taking control measures and paying particular attention to preventing its spread. It should not be allowed to escape elsewhere,” Jauni said.

The plant is not dangerous to people, but Jauni advised against canoeing or fishing in dense growths because the plant breaks into pieces and can spread. Dense stands are also unpleasant for swimming, while fragments can be carried to other waterways on fishing equipment.