Floating pennywort (Hydrocotyle ranunuculoides) is an invasive riparian plant native to South America and imported into the Netherlands and sold as a pond plant. Because some pond owners dumped surplus plants in the wild, the species was able to spread in various places. Small fragments of the plant that float with the water can grow into new foci elsewhere. Sales to consumers are now prohibited.
Floating pennywort is mainly found in nutrient-rich stagnant to weakly flowing water such as swamps, ponds, canals and ditches. Under favorable conditions, with summer temperatures like recent hot summers and with sufficient nutrients, floating pennywort will spread fast. Foothills several meters long can form within a few days, completely covering watercourses with dense, several decimetre thick floating mats of the Great pennywort.
Floating pennywort is plant that roots in banks of rivers & canals. The plant forms long stems with broad, kidney-shaped leaves that float on the surface of the water. The leaves can protrude up to 30 cm above the water surface. The petiole is located in the center of the leaf. Floating pennywort is easy to recognize by its broad and kidney-shaped leaves with a diameter of 4 to 10 centimeters. Propagation is done via rhizomes and floating stems. Pieces of broken stems also sprout into new plants.
The Great pennywort causes a lot of nuisance because:
- Light and oxygen can no longer penetrate the water, causing submerged aquatic plants and fauna to die.
- Native plant species are being displaced in the riparian zone.
- A lot of phosphate is released from the soil due to lack of oxygen as a result of the death of a large mass of pennywort.
- Landsliding of the riparian zone occurs through a combination of high biomass development and oxygen depletion (delayed digestion of plant material).
- There is an inhibiting effect on the supply and discharge of water, which increases the risk of flooding.
- Shipping, fishing and (swimming) recreation are hindered.
- There are financial consequences as a result of the control: invasive exotic riparian and water plants are generally difficult to control and can only be controlled at high cost.
- Unsafe situations can arise because it is unclear where the land/bank merges into the water.
Source: Kennisnetwerk Invasieve Exoten
Tibach-method: safe, environmental friendly and only one treatment required
Tests are currently being perfomed for treating the floating pennywort by freezing the soil of the banks. The first results look promising.
How it works
In the pond where floating pennywort occurs, we install stainless steel freezing lances. On this stainless lances we connect hoses to create a closed system. A 100% environmentally friendly coolant is pumped through this system, causing the soil to freeze. This causes the rhizomes to freeze and die.
Tibach method overview