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Salvinia molesta

Preferred Scientific Name: Salvinia molesta

Salvinia molesta is a free-floating aquatic plant, native to south-eastern Brazil. The weed is invasive in a variety of aquatic habitats, including lakes, rivers and rice paddies. As a result of the economic, environmental and social damage that has been caused by salvinia molesta, it has been ranked the second most noxious aquatic weed and is one of the world’s 100 worst invasive species. 

salvinia molesta
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Why is it a problem?

Salvinia molesta has been linked to a 12.5% fall in rice production in India. It has also been attributed to the death of livestock in infested areas, as it disguises areas of water, which the animals fall into and drown.

As well as smothering native fauna, salvinia molesta reduces the nutrients and sunlight which are available to other plants, causing them to die off and sink to the bottom of the water. This reduction in biodiversity also has implications for other species, such as benthic fish, which rely on the fauna.

The dense mats of salvinia molesta provide a habitat for mosquitos, which have been identified as transmitters of encephalitis, malaria and dengue fever.

Many villages in rural areas are reliant on aquatic transportation and fishing, yet it is difficult to manoeuvre canoes through the thick mats of salvinia molesta. Equally, the weed clogs irrigation systems and compromise drinking water supplies. 

Impacts

  • Clogs irrigation systems
  • Smothers native fauna
  • Loss of crops
  • Provides habitat for mosquitos 
  • Negatively impacts livelihoods

What’s the solution? 

Manual control

Manual removal of salvinia molesta can be practical in the very early stages on an invasion. However, due to rapid regrowth in established masses, manual control of a mature plant is highly impractical. 

Chemical control

Herbicides such as diquat and paraquat have shown to be effective in controlling infestations- if applied more than four times, a reduction in matt was noticeable between 10-14 days later.

Lab testing has also shown that household detergent can cause a 85% decrease in total chlorophyll and 75% decrease in total protein within 48 hours, when sprayed onto the plant. 

Biological control

The salvinia weevil (Crytobagus salviniae) has been used successfully to control salvinia spp. In parts of Africa and Asia, the weevil has been known to reduce an infestation to 1% of its former area.

However, the weevil only thrives in warm water temperatures, and has difficulties establishing in colder climates. Studies showed that salvinia weevil was not an effective biocontrol agent in areas of Australia, where climate is more unstable. 

Fact file

Name Salvinia molesta

Distribution

Asia, Africa, Americas and Carribbean, Europe and Oceania

For more information on distribution, view the full datasheet available here

Habitat

Freshwater

Natural enemies

Cyrtobagous salviniae, Cyrotagous singularis, Paulinia acuminate, samea multiplicalis

Invasiveness

Fast growing and has a high reproductive potential

Likelihood of entry

Highly likely to be accidentally spread internationally

Climate

Warm/Tropical

Plant Type

Aquatic

Further reading

Visit our online resource of research and full text articles and journals
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