Aquatic Plants

Biology and Control of Aquatic Plants, A Best Management Practices Handbook: Third Edition, written by Lyn A. Gettys, William T. Haller and David G. Petty, editors

Below is information from the Biology and Control of Aquatic Plants, A Best Management Practices Handbook: Controlling/Managing Weeds

When hand pulling a plant like Eurasian watermilfoil, the roots should be carefully dislodged from the bottom substrate so that the entire plant can be collected and removed to prevent vegetative regrowth.

Chapter 15.2: Eurasian Watermilfoil
John D. Madsen: Mississippi State University, Mississippi State MS; [email-obfuscate email=”jmadsen@gri.msstate.edu”]

Introduction and spread
Eurasian watermilfoil also became a serious problem in the hydropower and flood control reservoirs of the Tennessee River, where large-scale applications of herbicides were used in an attempt to eradicate the weed. Eurasian watermilfoil is still present in the TVA (Tennessee Valley Authority) system but has largely been displaced by hydrilla (Chapter 15.1).

Problems associated with Eurasian watermilfoil
Because Eurasian watermilfoil grows entirely underwater as a submersed aquatic plant, the range of water depths the species can inhabit is limited by light penetration and water clarity. A dense canopy often forms at the surface of the water, which interferes with recreational uses of water such as boating, fishing and swimming. Dense growth of Eurasian watermilfoil may also obstruct commercial navigation, exacerbate flooding or clog hydropower turbines. In addition, excessive growth of the species may alter aquatic ecosystems by decreasing native plant and animal diversity and abundance and by affecting the predator/prey relationships of fish among littoral plants. A healthy lake is damaged because heavy infestations of Eurasian watermilfoil lower dissolved oxygen under the canopy, increase daily pH shifts, reduce water movement and wave action, increase sedimentation rates and reduce turbidity.

Several herbicides can be used to effectively manage Eurasian watermilfoil. Contact herbicides – including diquat and endothall – provide good control, whereas systemic herbicides such as 2,4–D, fluridone and triclopyr provide excellent control. Herbicides should be selected based on site size and conditions, water exchange characteristics, potential water use restrictions, federal, state and local regulations and economic considerations (Chapter 11).

Chapter 11: Chemical Control of Aquatic Weeds
Michael D. Netherland: US Army Engineer Research and Development Center, Gainesville FL; [email-obfuscate email=”mdnether@ufl.edu”]

Chemical Chart for controlling milfoil:
Chemical Chart for controlling milfoil

2,4–D (1959) Several nuisance emergent and submersed plants are controlled by 2,4–D, but this herbicide is primarily used for selective control of waterhyacinth and Eurasian watermilfoil. A liquid amine formulation is used to control emergent and submersed plants and a granular ester formulation is used for submersed weed control. In addition, a granular amine formulation has been recently registered. Some native emergent plants – including waterlilies, spatterdock and bulrush – are susceptible to 2,4–D, so care should be taken to avoid injury to these plants. 2,4–D has been used for more than 50 years to control broadleaf weeds in pastures, crops, turf and aquatic systems.

Important Note: 2,4-D will not kill Brittle Leaf Naiad

Triclopyr (2002) Triclopyr was registered for aquatic use in 2002 and to date the major use of his herbicide has been for selective control of Eurasian watermilfoil. Similar to 2,4–D, there are certainly other plant species that are susceptible to triclopyr; however, the historical strength of auxin mimic herbicides has been selective control of invasives such as Eurasian watermilfoil or waterhyacinth. Triclopyr is registered as both liquid and granular amine formulations. Like 2,4–D, some native non-target emergent plants are susceptible to triclopyr, so care should be taken to avoid injury to these plants. The use of triclopyr in public waters is permitted in some states where 2,4–D use is not allowed. Triclopyr is also labeled for control of broadleaf weeds in turf, forestry and crop production.

Chemical Control Options for killing Brittle Leaf Naiad

Brittle Naiad, Marine Naiad


The active ingredients that have been successful in treating brittle naiad include diquat (E), endothall (E7), fluridone (E), and flumioxazin 7#40;E). E = excellent, G = good
Reward is a liquid diquat formulation that has been effective on brittle naiad. It is a contact herbicide. Contact herbicides act quickly and kill all plants cells that they contact.
Aquathol K, and Aquathol Super K dipotassium salts of endothall and comes in both liquid and granular formulations. These endothall products have been effective on brittle naiad. Contact herbicides act quickly and kill all plants cells that they contact.
Hydrothol 191 is an alkylamine salt of endothall and comes in both liquid and granular formulations. It is a contact herbicide and has been effective on brittle naiad. Contact herbicides act quickly and kill all plants cells that they contact. Hydrothol can be toxic to fish.
Sonar, Avast , and Whitecap are floridone compounds and comes in both liquid and granular formulations, and have been effective on brittle naiad. These are broad spectrum, systemic herbicides. Systemic herbicides are absorbed and move within the plant to the site of action. Systemic herbicides tend to act more slowly than contact herbicides.
Clipper is a flumioxazin product and comes in a water dispersible granule which must be mixed in water first and then either sprayed or injected. It is a broad spectrum, contact herbicide. Contact herbicides act quickly. Flumioxazin should be applied to actively growing plants and a surfactant will be needed if the herbicide is applied foliage of floating or emergent plants. Water pH needs to be below 8.5 or flumioxazin will rapidly degrade and lose effectiveness.

Chemicals for Controlling Milfoil

Aquatic Herbicides

Ecology currently issues permits for seven aquatic herbicides and two algaecides (as of 2006 treatment season) for aquatic plant treatment for lakes, rivers, and streams. Plant control in irrigation canals is covered under another permit. The chemicals that are permitted for use in 2006 under the Aquatic Plant and Algae Control Permit and the Noxious Weed Permit are:

Glyphosate

Trade names for aquatic products with glyphosate as the active ingredient include Rodeo®, AquaMaster®, and AquaPro®. This systemic broad spectrum herbicide is used to control floating-leaved plants like water lilies and shoreline plants like purple loosestrife. It is generally applied as a liquid to the leaves. Glyphosate does not work on underwater plants such as Eurasian watermilfoil. Although glyphosate is a broad spectrum, non-selective herbicide, a good applicator can somewhat selectively remove targeted plants by focusing the spray only on the plants to be removed. Plants can take several weeks to die and a repeat application is often necessary to remove plants that were missed during the first application.

Fluridone

Trade names for fluridone products include Sonar® and Whitecap®. Fluridone is a slow-acting systemic herbicide used to control Eurasian watermilfoil and other underwater plants. It may be applied as a pellet or as a liquid. Fluridone can show good control of submersed plants where there is little water movement and an extended time for the treatment. Its use is most applicable to whole-lake or isolated bay treatments where dilution can be minimized. It is not effective for spot treatments of areas less than five acres. It is slow-acting and may take six to twelve weeks before the dying plants fall to the sediment and decompose. When used to manage Eurasian watermilfoil in Washington, fluridone is applied several times during the spring/summer to maintain a low, but consistent concentration in the water. Granular formulations of fluridone are proving to be effective when treating areas of higher water exchange or when applicators need to maintain low levels over long time periods. Although fluridone is considered to be a broad spectrum herbicide, when used at very low concentrations, it can be used to selectively remove Eurasian watermilfoil. Some native aquatic plants, especially pondweeds, are minimally affected by low concentrations of fluridone.

2,4-D

There are two formulations of 2,4-D approved for aquatic use. The granular formulation contains the low-volatile butoxy-ethyl-ester formulation of 2,4-D (Trade names include AquaKleen® and Navigate®). The liquid formulation contains the dimethylamine salt of 2,4-D (Trade names include DMA*4IVM). 2,4-D is a relatively fast-acting, systemic, selective herbicide used for the control of Eurasian watermilfoil and other broad-leaved species. Both the granular and liquid formulations can be effective for spot treatment of Eurasian watermilfoil. 2,4-D has been shown to be selective to Eurasian watermilfoil when used at the labeled rate, leaving native aquatic species relatively unaffected. (Read Ecology’s risk assessment). By court-order the butoxy-ethyl-ester formulation of 2,4-D cannot be used in waters with threatened and endangered salmon-bearing waters in the Pacific Northwest.

Endothall

A trade name for the dipotassium salt of endothall is Aquathol®. Endothall is a fast-acting non-selective contact herbicide which destroys the vegetative part of the plant but generally does not kill the roots. Endothall may be applied in a granular or liquid form. Typically endothall compounds are used primarily for short term (one season) control of a variety of aquatic plants. However, there has been some recent research that indicates that when used in low concentrations, endothall can be used to selectively remove exotic weeds; leaving some native species unaffected. Because it is fast acting, endothall can be used to treat smaller areas effectively. Endothall is not effective in controlling Canadian waterweed (Elodea canadensis) or Brazilian elodea. (Read Ecology’s risk assessment for endothall)

Diquat

A trade name for diquat is Reward®. Diquat is a fast-acting non-selective contact herbicide which destroys the vegetative part of the plant but does not kill the roots. It is applied as a liquid. Typically diquat is used primarily for short term (one season) control of a variety of submersed aquatic plants. It is very fast-acting and is suitable for spot treatment. However, turbid water or dense algal blooms can interfere with its effectiveness. Diquat was allowed for use in Washington in 2003 and Ecology collected information about its efficacy against Brazilian elodea in 2003. A littoral zone treatment in Battle Ground Lake in Clark County Washington in 2003 resulted in nearly complete removal of Brazilian elodea in that water body. (Read Ecology’s risk assessment for diquat). Read the journal article about the Battle Ground Lake study.

Triclopyr-TEA

A trade name for triclopyr is Renovate3®. There are two formulations of triclopyr. It is the TEA formation of triclopyr that is registered for use in aquatic or riparian environments. Triclopyr, applied as a liquid, is a relatively fast-acting, systemic, selective herbicide used for the control of Eurasian watermilfoil and other broad-leaved species such as purple loosestrife. Triclopyr can be effective for spot treatment of Eurasian watermilfoil and is relatively selective to Eurasian watermilfoil when used at the labeled rate. Many native aquatic species are unaffected by triclopyr. Triclopyr is very useful for purple loosestrife control since native grasses and sedges are unaffected by this herbicide. When applied directly to water, Ecology has imposed a 12-hour swimming restriction to minimize eye irritation. Triclopyr received its aquatic registration from EPA in 2003 and was allowed for use in Washington in 2004. (Read Ecology’s EIS for triclopyr)

Imazapyr

A trade name for imazapyr is Habitat®. This systemic broad spectrum, slow-acting herbicide, applied as a liquid, is used to control emergent plants like spartina, reed canarygrass, and phragmites and floating-leaved plants like water lilies. Imazapyr does not work on underwater plants such as Eurasian watermilfoil. Although imazapyr is a broad spectrum, non-selective herbicide, a good applicator can somewhat selectively remove targeted plants by focusing the spray only on the plants to be removed. Imazapyr was allowed for use in Washington in 2004. (Read Agriculture’s risk assessment for imazapyr)

Adjuvants

There are a number of adjuvants (surfactants, stickers, sinking agents) allowed for use under the NPDES permits (follow this link for a list of products). Please consult the permit webpage and the latest permits for a list of the allowed products.

Tennessee – List of Aquatic Applicators