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Water-willow | Justicia americana

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Publication Number: P3735-41
View as PDF: P3735-41.pdf

Emergent | Native

A thick stand of tall, green plants grow in the middle of a pond.
Floating stand of water-willow.
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Line drawing of water-willow.
Multiple stems of water-willow feature small flower blooms and elongated leaves.
Water-willow stem and flower.

Water-willow, also known as American water-willow, is found throughout the eastern half of the United States. This species grows from slender rhizomes that expand over time to form large stands. You will most often find this plant along the shoreline, in shallow lakes and ponds, or in the shallow riffles of flowing water.

Stems may emerge 3 feet above water and have simple leaves that are arranged oppositely along the stem. Leaves are normally 3 to 6 inches when mature, sword-shaped, and medium-green.

Water-willow is sometimes confused with alligator weed, but it can be distinguished by its single showy, white and/or violet iris-like flowers. Alligator weed typically has spherical, clover-like, white flowers. Water-willow flowers produce dry, highly polished seeds in groups of four, and each seed is about one-tenth of an inch in length.

Management Value

Water-willow is a native species and an important component of natural waterbodies. Deer will eat the leaves, beavers and muskrats will eat the rhizomes, and bees and other insects use the pollen. In moderate densities, it makes excellent habitat for fish, amphibians, and aquatic invertebrates.

The growth rate of water-willow is moderate to rapid, quickly forming large colonies. It can be problematic in shallow ponds and should not be encouraged by most pond owners. However, for those who like aggressive management, it makes excellent fish habitat and can be introduced on small, shallow areas adjacent to deeper water. Take care to control any unwanted expansion early before the colonies grow to nuisance levels.

Recommended Controls

Option 1: 2,4-D (3.8-pound formulation). For each gallon of water, mix 1.0 ounce of 2,4-D and 1.3 ounces of non-ionic surfactant. Spray to wet all plants. Do not exceed annual herbicide rate limits as stated on the product label.

The best approach is to treat ponds with herbicides when the plants are actively growing and the water temperature is at least 60˚F. Multiple applications may be necessary to achieve eradication.

Read and follow all chemical label instructions, especially the section on the use of personal protection equipment.

Photo Credits Top: Mike Cline, Creative Commons; Middle: N. L. Britton and A. Brown, USDA.

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Funding provided by the Aquatic Nuisance Species Program of the U.S. Fish and Wildlife Service, Grant Award F18AP00260 to the Mississippi Department of Environmental Quality. Additional funding and support provided by the MSU Extension Service.

The information given here is for educational purposes only. References to commercial products, trade names, or suppliers are made with the understanding that no endorsement is implied and that no discrimination against other products or suppliers is intended.

Publication 3735-41 (POD-11-23)

By Wes Neal, PhD, Extension/Research Professor, Wildlife, Fisheries, and Aquaculture; Dennis Riecke, Fisheries Coordinator, Mississippi Department of Wildlife, Fisheries, and Parks; and Gray Turnage, PhD, Assistant Research/Extension Professor, GeoSystems Research Institute.

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Authors

Portrait of Dr. Wes Neal
Extension/Research Professor
Fisheries Extension
Asst Extension/Research Prof

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