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alligator weed seeds

Alligator weed grows in thick dense mats along the shoreline of lakes and streams creating difficulty for wildlife to access the edge of the water. Alligator weed doesn’t provide a sufficient food source or shelter for aquatic wildlife. By preventing native plants from growing, alligator weed removes necessary food sources and shelter for native animals.

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

Ecological Threat

U.S. Present: Alligator weed is found in the southwest United States from San Joaquin Valley south to Los Angeles and across the south and east portions of the continent south to Central America.

Holcomb, G. E. 1978. Alternaria alternantherae from alligatotorweed is also pathogenic on ornamental Amaranthaceae species. Phytopathology 68: 265-266.

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.

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

Three insect species have been introduced into the United States as biological controls:

Native to: South America


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

Thick mats of alligatorweed prevent drainage canals, ditches, streams, and other small waterways from emptying rapidly during periods of heavy water load, thus causing flooding. If mats break loose, they create obstructions by piling up against bridges, dams, and sharp bends in waterways. Thick mats also increase mosquito habitat. Navigation of small waterways is obstructed, as is shoreline navigation in large waterways. Fishing and swimming can be affected, although a small fringe of alligatorweed probably benefits fishing.

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

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

Requirements for land owners/occupiers and other persons if this pest is found can be sourced through the declared plant requirements link.

Pest and Disease Information Service (PaDIS)
+61 (0)8 9368 3080
[email protected]

Alligator weed (Alternanthera philoxeroides) is a declared pest in Western Australia (WA). This article describes the nature of the plant with links to requirements land owners/occupiers must adhere to and pest control methods.

Requirements for land owners/occupiers and other persons

Leaves: Dark green, opposite, joined directly to the stem (ie no leaf stalks) two to seven centimetres long, 5-40 millimetres wide. Blade – waxy surface and conspicuous veins radiating from midrib

Alligator weed spreads by stolons that grow outwards, forming new roots at the nodes. Short lengths of stem can break off and develop into a new plant. It forms seeds, but they do not appear to be viable in Australia, therefore spread is entirely by vegetative reproduction. It is a Weed of National Significance.

Flowers: Silvery white in spherical or cylindrical heads 1.2-1.4 centimetres diameter, borne on hairless or only slightly hairy stalks two to seven centimetres long arising from the leaf axils. Five petals five to six millimetres long, four-nerved and papery when dry.

Seed: Not quite round, and smooth surface, rarely, if ever produced in Australia.