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alligator weed seeds

U.S. Habitat: Alligator weed can grow in a variety of habitats from dry to immersed in water, but the preferred habitat is aquatic. In the United States alligator weed is most often found growing along the surface of streams and ponds at the shores edge.

Buckingham, G. R. 1996. Biological control of alligatorweed, Alternanthera philoxeroides, the world’s first aquatic weed success story. Castanea 61: 231-243.


Andres, L. A. 1977. The economics of biological control of weeds. Aquatic Botany 3: 111-123.

Barreto, R., R. Charudattan, A. Pomella, and R. Hanada. 2000. Biological control of neotropical aquatic weeds with fungi. Crop Protection 19: 697-703.

Physical removal of alligator weed is possible, but not usually 100% successful in eradicating the weed because the plant is able to re-grow and propagate from stem fragments alone. There are currently no biological control methods of eradication rather than goats which can keep the plant under control by feeding on the weed. Chemical control has been found to be the most successful when containing fluridone or imazapyr. Other chemical treatments have been found slightly less successful, but still effective when containing: 2,4-D, glyphosate, triclopyr, and imazamox. Systematic herbicides such as Navigate and Weedar 64 are successful chemical treatments as well.

Native to: South America

Alligatorweed was accidentally introduced into Florida in 1894 in ballast water of ships and can now be found growing throughout the state. This rooted perenial plant can grow in a variety of habitats, although it is usually found in water. It forms sprawling mats over deep rivers or along shorelinesand can be a pest on land.

Species Characteristics

Alligatorweed should be removed and disposed of properly to prevent spread.

Alligatorweed is listed as prohibited by the IFAS Assessment and is listed as a Category II by FLEPPC

Because alligatorweed spreads easily by fragmentation, attempts at physical control usually only serve to spread the weed.

Thank two tiny bugs that alligator weed, Alternanthera philoxeroides, isn’t a bigger problem than it already is.

Alligator weed is a plant of South American origin that made its way to Mobile, Ala., in 1897, most likely as a stowaway in a ship’s ballast accidentally dumped in state waters. It’s now found throughout the Southeast and, surprisingly, as far north Illinois and as far west as California. It’s also spread to Australia, Asia and parts of the Pacific, where it invariably becomes a herbaceous pest.

Both bugs are native to southern Brazil and northern Argentina and both feed exclusively on the leaves of alligator weed. Left uncheck, alligator weed will form large, dense mats that can choke navigation, clog drain and intake pipes, limit light penetration and block out native species. Waterways can become unuseable for boating, fishing and swimming. By decreasing water flow, it increases the amount sediment in the water and provides breeding places for mosquitos. When it grow on land, it can invade farm fields and become and agricultural pest (and potentially clogging irrigation ditches).

Alligator weed is listed on Florida’s prohibited aquatic plant list, and as a Category II invasive. That means it growing in abundance but not enough to have altered habitats. Yet. Which brings us to the heroes of our story: the alligatorweed flea beetle, Agasicles hygrophila, and the alligatorweed thrip, Amynothrips andersonii, both released in the U.S. back in the 1960s.

Australia considers alligator weed to be a "high risk" invasive despite an aggressive effort to limit its spread. In China, it’s ranked as the country’s 12th worst invasive; in some parts of China, it’s reduced rice production by 45 percent and sweet potato production by 63 percent.