All About Alligatorweed (Redux)

Alligatorweed (Alternanthera philoxeroides) is a common invasive plant that has plagued our state for well over 100 years. Native to Brazil, Paraguay, Argentina, and Uruguay, this plant was accidentally introduced to the Florida gulf coast in 1894 from ship ballast water. Along with water hyacinth (Eichornia crassipes), it was one of the original invaders of Florida and today it is found in almost every county in the state. This invasive plant has further naturalized throughout the South and mid-Atlantic regions and as far north as Illinois.

Alligatorweed prefers to establish along lake shorelines by rooting in the soft sediment. Its stems are hollow and will float. This allows the plant to aggressively expand across the top of the water where it helps facilitate the formation of floating tussocks. This quickly degrades native habitats and can severely impede access and navigation. Management of this plant is often essential and early efforts focused on mechanical harvesting. This was not successful as it was discovered that even small stem segments will float away, develop roots, and establish new populations in previously uninfested areas.

Alligatorweed Flea Beetle: A Florida Success Story

Jump ahead several decades when alligatorweed became the target candidate for classical biological control. Three insect species: a flea beetle (Agasicles hygrophila Selman and Vogt), thrips, (Amynothrips andersoni O’Neill) and stem borer (Arcola malloi Pastrana) were extensively studied. All three were discovered by entomologists in their native home range (South America) and released after rigorous quarantine testing within a span of eight years (1963-1971). These biocontrols have proven so successful that most people have forgotten that alligatorweed was once a problematic pest.

There are multiple herbicides known to be effective on alligatorweed, but these are rarely needed or recommended. In the last decade, less than 40 acres have been treated annually on Florida’s public water bodies. This is a testament to the success of the US Army Corps of Engineers alligatorweed flea beetle biocontrol release program a half-century ago. The US Army Corps of Engineers runs this program by collecting these insects in the wild each year and shipping them for release to control other plant populations outside of Florida. Alligatorweed has been in Florida for over 100 years and will likely remain for a hundred more, but through Integrated Pest Management (IPM) this plant will be kept in balance with the rest of the ecosystem.

Learn More About Alligatorweed

To learn more about alligatorweed, check out our podcast, “Working In The Weeds,” where we talk about all things aquatic and invasive plants. In our “Alligatorweed Deep Dive” episode, we discuss the native vs. invasive confusion, learn more from William Bartram, and explore why we need to manage this plant. Subscribe to our podcast for more episodes on all things invasive and aquatic plants.

This blog post was written by Dr. James Leary, faculty member with UF/IFAS CAIP. Questions or comments can be sent to the UF/IFAS CAIP communications manager at caip@ifas.ufl.edu. Follow UF/IFAS CAIP on Instagram, Facebook, and Twitter. Subscribe for more blogs like this one. 

UF/IFAS Center for Aquatic and Invasive Plants. Turning Science Into Solutions.

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