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Alligatorweed invasive aquatic weed

Alligatorweed is an underwater rooted, water-level emergent weed.

Alligatorweed, Alternanthera philoxeroides, is a perennial rooted emergent weed. The plant begins its growth rooted in the bottom of the pond, grows up, and emerges from the water.

Narrow sword-like leaves grow off opposite sides of a hollow stem. The stems can vary in color from green to red. This aquatic plant produces a small white flowers on the stem.

Alligator weed is also known as pigweed or alligator grass. Alligatorweed is commonly confused with smartweed. See the comparison below.


Where Does Alligatorweed Grow?

Alligator weed grows in shallow water areas near the shoreline. It can be found throughout the United States in ponds, lakes, streams, rivers and marshes.

While alligator weed is rooted along shorelines, growth spreads across the water surface. Dense alligatorweed mats can break off and float freely throughout the water body.

How Does Alternanthera philoxeroides Spread?

Stems of this invasive plant have nodes from where other stems will grow.

Vegetation can spread easily from broken pieces of vegetation. Mechanical removal is not recommended because it increases the chances of spreading from floating fragments.


Is Alligator weed Good or Bad for my Pond?

Alligatorweed is an invasive plant and is not native to the United States. This plant grows in thick dense mats along the edges of a pond. The mats make it very difficult for wildlife to reach the shoreline of the pond or lake.

The dense mats can overtake the full shoreline area. This prevents beneficial native plants, plants that wildlife uses for shelter and food, from being able to grow near the edges of the pond. Eventually, these mats will break off from the rooted part of the alligator weed and float freely in the pond.

Alligator weed can be damaging to the overall ecosystem of the pond, affecting both plants and animals. Facilitating the growth of alligatorweed is strongly discouraged as it is an invasive species.

How to Get Rid of Alligatorweed?

Alligatorweed control can be difficult due to its quick spreading nature. Alligatorweed can be trimmed, but will regrow from roots and stems left behind. If manual removal, maintenance will be necessary repetitively.

Aquatic herbicides are the most effective way to remove Alligatorweed. Herbicides will kill the plant down to the roots, preventing regrowth.

Best Chemical Control to Kill Alligatorweed

Propeller is the best aquatic herbicide to use for eliminating alligatorweed. Propeller acts rapidly to kill the pond weeds.

Other Herbicides to Kill Alternanthera philoxeroides

Clearcast is another herbicide that can be used to control Alligator weed. Clearcast will act in a slower manner than Propeller. Imazamox is a safer alternative to glyphosate. It is effective on the portions of the weed that are above the surface of the water.

Alligator weed and smartweed are often confused with one another. Here are some of the easiest ways to tell the difference.


  • Blooms a white flower
  • Produces a hollow stem
  • Leaves grow out on opposite sides of the stem


  • Leaves come down and wrap around the stem
  • Leaves grow out alternate from the stem

Alligator Weed Control

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