Aquatic invader, European Frogbit, affected by shading treatments

New York study suggests non-chemical shading treatments can reduce plant biomass of European Frogbit (Hydrocharis morsus-ranae L.).

Invasive European Frogbit grows in dense floating mats. Photo Credit: Jane Herbert
Invasive European Frogbit grows in dense floating mats. Photo Credit: Jane Herbert

According to the Midwest Invasive Species Information Network, the occurrence of the invasive aquatic plant known as European Frog-bit has so far been limited to the east side of our state. The discovery of a Frog-bit infestation in Alpena in 2013 is detailed in a previous Michigan State University Extension article.

Resembling a small water lily, European Frog-bit is an attractive aquatic plant and a favorite of water gardeners. It grows in a dense mat and can out compete native plants for space and light. As there is no aquatic herbicide proven safe and effective in the treatment of this escapee other control measures must be explored. Researchers in New York published a study in June 2014 detailing their investigation of the use of shade as a possible control measure.

Previous studies have shown that, like many plants, European Frog-bit is dependent upon light for growth and light-deprivation may significantly reduce plant biomass. This research project was conducted in a greenhouse (under controlled temperature and light conditions) and also in a sheltered inlet on Oneida Lake – one of the New York Finger Lakes. Plants were covered with a range of densities of shade cloth to block out some or all light.

Results of the New York study indicated that, under greenhouse conditions, 50 percent or greater shading affected frog-bit growth and no plants survived at 100 percent shading levels. Results of the in-lake study indicated that biomass was significantly reduced by 70 percent or greater shading. Overall, the effects of shading on in-lake water temperatures, dissolved oxygen and existing submerged plant communities were varied.

For a more in-depth summary of the New York study findings, along with a link to the full study, please visit the Lake Scientist website. A handy boater’s guide to selected aquatic invasive plants is available from Michigan State University Extension. 

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