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# Aquatic Plant Management - Aquatic Herbicides Description of Method
Aquatic herbicides are chemicals specifically formu lated for use in water to kill or control aquatic p lants. Herbicides approved for aquatic use by the United S tates Environmental Protection Agency (EPA) have been reviewed and are considered compatible with th e aquatic environment when used according to label directions. However, some individual states, includ ing Washington, also impose additional constraints on their use. Aquatic herbicides are sprayed directly onto floati ng or emergent aquatic plants or are applied to the water in either a liquid or pellet form. Systemic herbicidesare capable of killing the entire plant. Contact herbicidescause the parts of the plant in contact with the h erbicide to die back, leaving the roots alive and able to regrow. Non-selective , broad spectrum herbicides will generally affect a ll plants that they come in contact with. Selective herbicides will affect only some plants (often dico ts - broad leafed plants like Eurasian watermilfoil ( Myriophyllum spicatum ) will be affected by selective herbicides whereas monocots like Brazilian elodea ( Egeria densa ) may not be affected). Most aquatic plants are monocots. Because of environmental risks from improper application, aquatic herbicide application in Washington state waters is regulated and has the following restrictions: Applicators must be licensed by the Washington State Department of Agriculture. Because of a March 2001 court decision (9th Circuit District Court), applicants must obtain coverage under a discharge permit called a National Pollutant Elimination System Discharge (NPDES) permit before they can legally apply aquatic herbicides to the waters of the state. Ecology requires notification and posting before tr eatment and there are additional mitigations to protect rare plants or threatened and endangered sp ecies. Ecology issued a "lake" NPDES general permit March 1, 2006 to cover the management of in-lake noxious weeds and native aquatic plants and algae. The Wash ington Department of Agriculture also has a general NPDES permit for the management of noxious weeds gr owing in wet areas such as freshwater wetlands, rivers, and estuaries. More information about permits for the application of aquatic pesticides. For in-lake projects applicators and/or the state o r local government sponsoring the project must obta in coverage under Ecology's Aquatic Plant and Algae Ma nagement NPDES permit before applying herbicides. For non-lake projects involving the treatment of no xious weeds in wet areas and estuaries, government sponsors and other entities can "contract" with the Washington Department of Agriculture under their NPDES permit for noxious weed control. Aquatic Plant Management - Aquatic Herbicides http://www.ecy.wa.gov/programs/wq/plants/management /aqua028.html

1 of 5 1/11/2016 4:52 PMFind out how to go about contracting with Agricultu re to manage state-listed noxious weeds. 

### Aquatic Herbicides Ecology currently issues permits for seven aquatic herbicides and two algaecides (as of 2006 treatment season) for aquatic plant treatment for lakes, rive rs, and streams. Plant control in irrigation canalsis covered under another permit. The chemicals that ar e permitted for use in 2006 under the Aquatic Plant and Algae Control Permit and the Noxious Weed Permi t are: Glyphosate Trade names for aquatic products with glyphosate asthe active ingredient include Rodeo®, AquaMaster®, and AquaPro®. This systemic broad spectr um herbicide is used to control floating-leaved plants like water lilies and shorel ine plants like purple loosestrife. It is generally applied as a liquid to the leaves. Glypho sate does not work on underwater plants such as Eurasian watermilfoil. Although glyphosate is a broad spectrum, non-selective herbicide, a good applicator can somewhat selective ly 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 tha t were missed during the first application.

Fluridone Trade names for fluridone products include Sonar® a nd Whitecap®. Fluridone is a slow-acting systemic herbicide used to control Eurasian watermi lfoil and other underwater plants. It may be applied as a pellet or as a liquid. Fluridone ca n show good control of submersed plants where there is little water movement and an extende d time for the treatment. Its use is most applicable to whole-lake or isolated bay treatmentswhere dilution can be minimized. It is not effective for spot treatments of areas less than fi ve acres. It is slow-acting and may take six to twelve weeks before the dying plants fall to the se diment and decompose. When used to manage Eurasian watermilfoil in Washington, flurido ne is applied several times during the spring/summer to maintain a low, but consistent con centration in the water. Granular formulations of fluridone are proving to be effecti ve when treating areas of higher water exchange or when applicators need to maintain low l evels over long time periods. Although fluridone is considered to be a broad spectrum herb icide, when used at very low concentrations, it can be used to selectively remov e Eurasian watermilfoil. Some native aquatic plants, especially pondweeds, are minimallyaffected by low concentrations of fluridone.
2,4-D There are two formulations of 2,4-D approved for aq uatic use. The granular formulation contains the low-volatile butoxy-ethyl-ester formul ation of 2,4-D (Trade names include AquaKleen® and Navigate®). The liquid formulation con tains the dimethylamine salt of 2,4-D (Trade names include DMA*4IVM). 2,4-D is a relative ly fast-acting, systemic, selective herbicide used for the control of Eurasian watermil foil and other broad-leaved species. Both the granular and liquid formulations can be effecti ve 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 relati vely unaffected. ( Read Ecology’s risk assessment ). By court-order the butoxy-ethyl-ester formulatio n of 2,4-D can not be used in waters with threatened and endangered salmon-bearin g 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 i n a granular or liquid form. Typically endothall compounds are used primarily for short te rm (one season) control of a variety of Aquatic Plant Management - Aquatic Herbicides http://www.ecy.wa.gov/programs/wq/plants/management /aqua028.html

2 of 5 1/11/2016 4:52 PMaquatic plants. However, there has been some recentresearch that indicates that when used

in low concentrations, endothall can be used to sel ectively remove exotic weeds; leaving some native species unaffected. Because it is fast actin g, endothall can be used to treat smaller areas effectively. Endothall is not effective in co ntrolling 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 butdoes 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 an d is suitable for spot treatment. However, turbid water or dense algal blooms can interfere wi th 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 treatmentin Battle Ground Lake in Clark County Washington in 2003 resulted in nearly complete remo val 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 u se 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 broa d-leaved species such as purple loosestrife. Triclopyr can be effective for spot treatment of Eu rasian watermilfoil and is relatively selective to Eurasian watermilfoil when used at the labeled r ate. 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 minim ize eye irritation. Triclopyr received its aquatic registration from EPA in 2003 and was allow ed for use in Washington in 2004. ( Read Ecology's EIS for triclopyr )
Imazapyr A trade name for imazapyr is Habitat®. This systemi c broad spectrum, slow-acting herbicide, applied as a liquid, is used to control emergent pl ants like spartina, reed canarygrass, and phragmites and floating-leaved plants like water li lies. Imazapyr does not work on underwater plants such as Eurasian watermilfoil. Although imaz apyr is a broad spectrum, non-selective herbicide, a good applicator can somewhat selective ly remove targeted plants by focusing the spray only on the plants to be removed. Imazapyr wa s allowed for use in Washington in 2004. ( Read Agriculture's risk assessment for imazapyr ) 

### Adjuvants There are a number of adjuvants (surfactants, stick ers, 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 pr oducts. 

### Algaecides

Endothall - Amine Salt

A trade name for the amine formulation of endothall is Hydrothol 191®. Hydrothol 191® is a rapidly acting non-selective contact herbicide or a lgaecide. In Washington Hydrothol 191® may only be used at very low concentrations for fil amentous algae control or cyanobacteria control (blue-green algae) in selected waterbodies. Several treatments each season may be Aquatic Plant Management - Aquatic Herbicides http://www.ecy.wa.gov/programs/wq/plants/management /aqua028.html

3 of 5 1/11/2016 4:52 PMneeded to control algae/cyanobacteria. Hydrothol 19 1® has a high acute toxicity to fish and

must be used with extreme care. Because of fish imp acts, Ecology does not allow concentrations higher than 0.2mg a.e./L of Hydrotho l 191®. Unlike copper compounds that are also used for algae control, Hydrothol 191® doesnot accumulate in sediments and breaks down rapidly. There are water use restrictions asso ciated with the use of Hydrothol 191® in Washington. ( Read Ecology’s risk assessment ) Peroxygen-based Granular Algaecide
Trade names include GreenClean® and Pak27®. These are peroxygen-based granular algaecides used for the prevention and control of a lgae in ponds, streams, irrigation systems, ornamental pools, and fountains. Areas being treate d with these products must be closed to recreational activities during and for two-hours af ter treatment. ( Read a human and environmental risk assessment ). Copper Compounds Copper compounds are no longer allowed for aquatic use in Washington state waters except under the NPDES permit for Irrigation Districts. ( Read Ecology's risk assessment ). 

### Advantages Aquatic herbicide application can be less expensive than other aquatic plant control methods, especially when used in controlling wide-spread infestations of state-listed noxious aquatic weeds. Aquatic herbicides are easily applied around docks and underwater obstructions. Washington has had some success in eradicating Eura sian watermilfoil, a state listed noxious weed, from some smaller lakes (350 acres or less) using a quatic herbicides. 

### Disadvantages Some herbicides have swimming, drinking, fishing, i rrigation, and water use restrictions (check the label and general permit). Herbicide use may have unwanted impacts to people w ho use the water and to the environment. Non-targeted plants as well as nuisance plants may be controlled or killed by some herbicides. Depending on the herbicide used, it may take severa l days to weeks or several treatments during a growing season before the herbicide controls or kil ls treated plants. Rapid-acting herbicides like endothall and diquat m ay cause low oxygen conditions to develop as plants decompose. Low oxygen can cause fish kills. To be most effective, generally herbicides must be applied to rapidly-growing plants, although sometimes fall applications of perennial plants can also be effective. Some expertise in using herbicides is necessary in order to be successful and to avoid unwanted impacts. Many people have strong feelings against using chem icals in water. Find out what your neighbors think about chemical use before deciding to treat y our water plants with herbicides. Some cities or counties may have policies forbiddin g or discouraging the use of aquatic herbicides. Check before hiring an aquatic herbicide applicator

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### Permits An NPDES permit is needed to apply any aquatic pest icide (including herbicides) to waters of the state

. Some herbicide residue monitoring may be required a nd there is a permit fee for coverage under the Aquatic Plant and Algae Management permit. For aqua tic plant or algae management in lakes (includes both noxious weeds and native plants and algae) app ly to Ecology for coverage. For noxious weed control in wet areas, estuaries, a nd shorelines only apply to the Washington Aquatic Plant Management - Aquatic Herbicides http://www.ecy.wa.gov/programs/wq/plants/management /aqua028.html

4 of 5 1/11/2016 4:52 PMDepartment of Agriculture to contract with them und er their NPDES Aquatic Noxious Weed Control permit each treatment season. There is no fee to become a contractor under Agriculture's permit. However, the targeted weeds must be on the Washington’s Noxious Weed List or on Agriculture’s quarantine lists. 

### Costs of Herbicide Treatment These costs are estimates and will vary from site t o site depending on treatment rates, water depths, amount of notification needed, difficulty of accessto the site, and other factors. Approximate costs for one acre herbicide treatment: Glyphosate: $300, Flurido ne: $900 to $1,000, Endothall: $650, 2,4-D: $300-600, Diquat: $300 to $400 Read about an innovative approach to using aquatic herbicides. Questions about this page? Contact us

. Copyright © Washington State Department of Ecology. See http://www.ecy.wa.gov/copyright.htm Aquatic Plant Management - Aquatic Herbicides http://www.ecy.wa.gov/programs/wq/plants/management /aqua028.html

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