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Common Aquatic Plant Management Problems

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Freshwater Fisheries Section

Please note:
This information is intended for educational purposes only. References to commercial products or trade names are made with the understanding that no discrimination is intended of other products which may be available. Any herbicides recommended herein for the treatment of aquatic vegetation have been registered by the Environmental Protection Agency for use in the manner described. The registration and use of a particular product may change therefore the information provided here may not remain current indefinitely. It is the responsibility of the user to read and follow the manufacturer's label to prevent misuse of the product.

Variable-Leaf Milfoil

Variable-Leaf Milfoil

Scientific Name - Myriophyllum heterophyllum
Common Name - Water milfoil/Coontail/Coontail Moss

Distribution and Habitat

Milfoil is found predominately in the upper and lower coastal plain. It thrives in older, more stabilized systems with clear, acidic water, where it may be rooted in depths up to 10 feet. It is very common in impoundments located in the sandhills region of the midlands. The dense growth characteristics of this plant often dominates all other aquatic growth and can seriously restrict utilization of the water body for recreation or other purposes.


Description

Milfoil is a rooted aquatic species possessing a long, robust stem which is usually deep red or brownish red in color. This plant may exhibit two distinctly different leaf forms. The submerged leaves are fine, numerously dissected and are located in whorls along the stem, giving milfoil a delicate feather-like or "coontail" appearance. This portion of the plant is usually a reddish or greenish brown in color. The emergent leaves are found in whorls on a stalk-like portion of the stem which extends 6 - 8 inches above the water. These small leaves are bright green and oval in shape. This growth aspect of the plant is so different from the submerged portion that it is often mistaken as being another plant altogether. This emergent growth is generally associated with mature stages of milfoil and may not be evident until late summer. The flowers of water milfoil are located on the emergent shoots and are very small and inconspicious, thus are not considered a good identifying characteristic for the untrained observer.


Recommended Control Methods

1. Granular 2, 4-D

Active Ingredients: Ester of 2, 4-Dichlorophenoxyacetic acid
Product Name: Aqua-Kleen; Riverdale; Weedtrine II
Approximate Cost: $1.80/lb. - $90.00/50lbs.
Application Rates: 100-150 lbs/acre (100 lbs/acre is equivalent to approximately 5 lbs/2000 sq. ft.)

Application Methods and Tips: Best results will be achieved when the herbicide is applied during the spring or early summer. Affects of the herbicide may not be noticeable for four to six weeks after treatment. Granular 2, 4-D should be applied in a broadcast fashion by the use of a fertilizer or seed spreader to ensure uniform coverage of the treatment area. Generally, control will be confined only to those areas in which the herbicide is applied, thus allowing spot treatment of selected areas where weed control is desired. Higher application rates will be required in situations of dense weed growth, water greater than five feet deep or ponds with a short retention time (high volume turnover). Follow-up applications may be required to gain desired control. Care should be exercised when treating ponds with dense growths of vegetation to prevent oxygen depletions due to decomposing plants. No more than one-third of the pond should be treated at once, allowing 14-21 day intervals between applications. Additional product directions and precautionary statements are listed on the herbicide container. READ AND FOLLOW THE HERBICIDE LABEL.

2. Diquat Dibromide

Active Ingredients: Diquat dibromide salt
Product Name: Reward; Weedtrine D; Aqua-Clear
Approximate Cost: $90.00 - $100.00/gal.
Application Rates: 1-2 gal/surface acre

Application Methods and Tips: In areas of early growth or light infestations, evenly distribute herbicide by pouring over the treatment area in strips 40 feet apart. Dilution with water may be required in order to adequately cover the treatment area. In dense growth situations, the higher rates should be used and the herbicide should be injected below the surface in strips 20 feet apart. Treatment of water milfoil with this herbicide is more effective in low flow situations. Do not apply dibromide in muddy water as the herbicide will be inactivated. Additional product directions and precautionary statements are listed on the herbicide container. READ AND FOLLOW THE HERBICIDE LABEL.

Other herbicides registered for the control of water milfoil:

  • Sonar AS
  • Sonar SP
  • Aquathol
  • Aquathol K

Consult the fisheries biologist serving your county
for more details concerning use of these products.

3. Sterile Grass Carp (White Amur)

Grass carp are generally not considered an effective alternative for the control of established infestations of water milfoil. They may be utilized as a preventative measure or in situations in which the weed growth has been significantly reduced with herbicides, but should not be stocked as the initial or primary means of controlling water milfoil.

Variable-Leaf Milfoil PDF

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