Water lettuce and hyacinth growing togetherjpg

Water lettuce growing with water hyacinth (darker, shiny plant).


This invasive species forms dense mats on the water’s surface, causing dramatic changes to ecosystems [3, 6, 7]. These mats can block sun light needed by native submerged aquatic plants, decrease dissolved oxygen levels leading to fish kills, harbor disease-carrying insects like mosquitos, and impede the movement of aquatic organisms [6, 8, 9]. Water lettuce can also have negative consequences for boaters and fisherman, as dense mats can inhibit boat travel [5, 6, 8]. This plant also poses problems for hydroelectric dams as they can clog turbines and water intake pumps [2, 3].


Figure_10jpgDistribution of water lettuce in Louisiana. This plant may be found in other parishes not highlighted in green on the map. Image courtesy of EDDMaps.

According to the U.S. Geological Survey, water lettuce was first observed in Louisiana waters in Cameron Parish in 1958 [8]. Since then, the plant has spread to at least 25 parishes, mostly in southern Louisiana.

Mechanical and chemical removal

Water lettuce can be controlled through mechanical methods using harvesters to remove the plants and booms to contain infestations [8, 9]. However, these techniques can be very costly [9]. Another popular method of control is the use of herbicides such as diquat, glyphosate, and 2,4-d [8, 9]. Mycoherbicides containing toxin-producing fungi that damage plant tissues are also used [9].


Currently, there are two biological control agents being used to control this plant within the US: the Asian water lettuce moth (Spodoptera pectinicornis) and the water lettuce weevil (Neohydronomus affinis). The water lettuce weevil has been very successful at controlling water lettuce in the US and abroad. Unfortunately, however, the release of the Asian water lettuce moth for biocontrol has mostly been viewed as a failure.[1]

Author: Seth Spinner

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The LSU AgCenter and the LSU College of Agriculture