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alligator weed seed

See Using herbicides for more information.

In the Sydney Basin, alligator weed is currently threatening the turf industry valued at over $50 million annually. The vegetable industry valued at $150 million annually is also under threat in the Hawkesbury–Nepean catchment. The extraction industry in the Hawkesbury–Nepean is also under threat. This industry supplies most of Sydney’s sand, gravel and soil resources. If contaminated, the movement of these resources would be severely restricted. Sugar cane and soy bean industries are also threatened in the Richmond catchment.

PERMIT 14733 Expires 30/06/2024
Metsulfuron-methyl 600 g/kg (Various products)
Rate: 1 g in 10 L of water
Comments: For control in urban and residential backyards.
Withholding period: Nil (recommended not to graze for 7 days before treatment and for 7 days after treatment to allow adequate chemical uptake in target weeds).
Herbicide group: B, Inhibitors of acetolactate synthase (ALS inhibitors)
Resistance risk: High


Julien, MH (19950. Alternanthera philoxeroides (Mart.) Griseb. In (Eds) R.H. Groves, R.C.H. Shepherd and R.G. Richardson, The Biology of Australian Weeds, Volume 1.

Julien, MH and Stanley, JN (1999). The management of alligator weed. Proceedings of the 10th Biennial Noxious Weeds Conference, Ballina July 20–22 1999, pp 2–13.

Plant material can be dried and incinerated, boiled or microwaved. Large volumes of contaminated soil are difficult to process, and if possible need to be spread on an impenetrable surface and dried prior to burial (preferably sealed in containers) at a secure disposal site that can be monitored for any signs of regrowth.

The Alligator Weed Control Manual (see More Information) provides a comprehensive overview of the various chemical, physical and biological control options. Management options for alligator weed depend on the site and location of the infestation, its age and extent and the resources available. Any new infestation should be assessed to determine if immediate eradication is a feasible management objective (small numbers of scattered plants; infestations up to 5 m x 5 m). If not, management should aim for suppression leading to eradication over a period of approximately 6 years (infestations with roots more than 1 m deep; areas of infestation over 10 m x 10 m), or ongoing suppression (in extensive, long established infestations).

Part of the reason why alligator weed is such a problem is that it is one tough, adaptable plant. It will grow in water, it will grow on land. It will tolerate a fair amount of salt. It will also tolerate cold to a degree, dying back come winter in colder climates. By the way, the alligatorweed flea beetle is ineffective on alligator weed when it grows on land.

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

It’s also nutritious when cooked as a green, full of minerals and a fair share of protein. However, it also tends to pick up any toxins that might be present in the water, including heavy metals.

Alabamba. Arizona, Arkansas, California, South Carolina and Texas all considered it to be a noxious weed.

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.

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).

It can form sprawling mats over rivers or along shore lines, but it can also grow on dry land. Its leaves are elliptical to oblong in shape and grow opposite each other along its fleshy stem. The outer edges of the leaves are smooth, what botanists call complete. The stems themselves can exceed 30 feet in length. It blooms during summer, the flowers tiny, white-and-yellow, clustered on a head the size of a marble. Alligator weed apparently does not reproduce via seed in North America but rather vegetatively. It has nodes along the stems where roots and new stems grow. Break off a piece and you’ve got a new plant. By contrast, according to the authoritative Flora of North America, neither the fruit of the plant or its seed has been observed.