University of FloridaSolutions for Your Life

Download PDF
Publication #SS-AGR-44

Efficacy of Herbicide Active Ingredients Against Aquatic Weeds1

S. F. Enloe, M. D. Netherland, W. Haller, and K. Langeland2

Weed control is often a critical component of aquatic vegetation management in Florida waters. While physical, mechanical, and biological controls are utilized where they are feasible, herbicides are the primary tool used to control many troublesome species. This document answers some common questions and provides efficacy information for all herbicide active ingredients labeled for aquatic use in Florida.

Do I need a license or permit to make an aquatic application?

Pesticide licenses and aquatic application permits are two separate issues. Regarding licensing, anyone who applies herbicides commercially or for a public agency should be licensed as a Restricted Use Pesticide (RUP) applicator. Information pertaining to RUP applicator training and licensing can be obtained from your local county Extension office or from the UF/IFAS Pesticide Information Office (https://pested.ifas.ufl.edu/). Individuals who choose to apply herbicides to their own ponds should attain a basic understanding of herbicide application and ecology through RUP certification training (for more information on this topic, see EDIS publication PI-26, Licensing of Aquatic Herbicide Applicators in Florida, at http://edis.ifas.ufl.edu/PI011). However, in many instances, it is recommended that private pond owners employ a reputable aquatic plant management company to maintain their pond(s) through a service contract, especially if the pond has been neglected or is severely infested by difficult species.

Regarding permitting for aquatic applications, a permit from the Florida Fish and Wildlife Conservation Commission is required for control of weeds in public waters and waters with multiple ownership. No permits are required for private owners of ponds smaller than 10 surface acres in size if there is no connection to Waters of Special Concern. For more information, visit the FWC aquatic plant removal website: http://myfwc.com/license/aquatic-plants/permit-rules/.

Are there any water use restrictions after an herbicide application?

Label instructions for aquatic use may restrict the use of water for a given period of time for various purposes, including irrigation, mixing agricultural sprays, domestic use, swimming, fishing, watering livestock, or consuming fish from treated water. Herbicide labels provide these potential restrictions clearly and should be consulted before the product is used.

Can I use an herbicide to control an aquatic plant not listed on the label?

It is legal to use an herbicide to attempt to control a plant species that is not listed on the label as long as the product is labeled for use on the site. Registrants, those companies responsible for the herbicide label, are not required to list all possible species on a label that are susceptible to a given herbicide. In many cases, they only list the most commonly managed plants. Registrants are not liable if an end user attempts to use a product to control a plant not on the label and the product does not work.

How is herbicide efficacy (weed control) defined in this publication?

Efficacy is not defined as a silver bullet (i.e., where one treatment completely eradicates the target weed). Efficacy is typically defined as a substantial reduction of the target plant that results in a diminishment of its negative effects on the system. There is also a temporal element involved. In aquatics, this is typically within the range of a few weeks to a few months for free floating plants and algae, to a single growing season or entire year for many submersed and emergent plants. Tables 1 through 3 use the following codes: NR=Not recommended; F=Fair; G=Good; E=Excellent. Blank cells indicate insufficient data. The NR code is assigned where a given treatment will not provide any meaningful control of a target plant. The F code is assigned where some control occurs following treatment, but it may be inconsistent or short-lived. The G code is assigned where commercially acceptable control is generally achieved. The length of control may still vary by species. The E code is assigned where the target plant is highly sensitive to the herbicide and greater than 90% control is expected. An E code does not guarantee eradication, which is the elimination of all living parts of the plant that may include seeds, shoots, roots, rhizomes, stolons, and spores. Eradication is often exceedingly difficult, if not impossible, to achieve for many species.

Should I apply herbicide to the foliage of plants or just treat the water?

All herbicides are different and the labels need to be reviewed before purchasing a product. For example, glyphosate and imazapyr only control weeds by foliar applications and do not work if applied to the water. Several other herbicides may be applied to the water to control submersed weeds, but need to be applied to the foliage to be effective on emergent, floating, or floating leaved plants. Diquat is a good example of this. It is very effective against water lettuce when applied as a foliar spray, but it is not effective if simply applied to the water as a whole pond treatment. There are several other herbicides which can have both in-water and foliar uses, but effective control depends greatly on the way the herbicide is applied and the target species. Typically, granular or pelleted formulations are not effective for free floating or emergent plant control. Applicators must read the herbicide labels to select the most effective herbicide and choose the correct formulation and application strategy.

Where can I find herbicide labels online?

Herbicide product labels can be obtained from Crop Data Management Systems, Inc. (http://www.cdms.net), www.greenbook.net, or manufacturer representatives or their websites. Additionally, the Florida Department of Agriculture and Consumer Services (FDACS) Division of Agricultural Environmental Services maintains a list with reference to the active ingredients of all pesticide products registered for use in Florida. Remember that specific product information should be obtained from the product label. Label instructions must be followed for any herbicide application.

Which herbicides can be used in aquatic environments?

Only those herbicide products that are registered and labeled for application directly to water by the US Environmental Protection Agency (EPA) and FDACS may be used in Florida to control weeds growing in water. Active ingredients that are contained in aquatic herbicide products may also be present in products that are not approved for aquatic uses. However, it is not legal to apply an herbicide directly to water unless the herbicide label has specific instructions for application to water. All herbicide active ingredients labeled to date for use in Florida are listed in Tables 1 through 3.

Tables 1 and 2 are a quick reference of the effectiveness of herbicide active ingredients for control of common aquatic weeds. Table 3 addresses algae control. The tables are a species by herbicide matrix of known efficacy. Tables 1 and 3 list all herbicides classified as fast-acting, which are also called contact herbicides. Table 2 lists all herbicides classified as systemic. The species are grouped according to growth form (free floating, floating leaved, submersed, emergent, and algae). The herbicides are grouped by mode of action according to the Weed Science Society of America’s classification system and the Herbicide Resistance Action Committee codes.

Sensitivity of the target weed to the active ingredient is only one consideration in choosing the appropriate herbicide product. Other factors that may be important in such a decision include water uses, other plant species present, toxicity to fish and other organisms, and additives in individual products. These considerations and other important aspects of aquatic weed control are discussed more fully in other publications, such as the Aquatic Pest Control Applicator Training Manual (SM 3), available from the IFAS Extension Bookstore (http://ifasbooks.ifas.ufl.edu/).

Specific Notes on Free Floating Plant Control

As the name implies, many free floating plants move around with wind or water currents. One strategy is to treat after wind has consolidated plants in one open area of the pond. This does not always work, however, as wind may push free floating plants back into stands of emergent vegetation where treatment becomes more difficult. Many free floating plants can also survive along the shoreline in muddy conditions for a short time. Another consideration is the incredible growth rate exhibited by many free floating plants. Many plant populations can double in size in just a few weeks. This warrants aggressive treatment when populations are small to prevent the species from covering the entire pond. Many fast-acting systemic herbicides are effective on free floating plants. Additionally, surfactants often improve herbicide control of many free floating plants.

Specific Notes on Floating-Leaved Plant Control

Floating leaved plants, which anchor into the sediment and have leaves that remain at or near the water surface, can be difficult to control. Foliar herbicide treatments can be easily washed off the leaf surface with minimal wave action. Crested floating heart and watershield are good examples of this issue. Systemic herbicides are generally recommended more than contact herbicides for floating leaved plant control. Surfactants often improve control of many floating leaved plants.

Specific Notes on Submersed Plant Control

For submersed plants, the applicator is treating the water column and not the plants directly. The herbicide is applied to the water and quickly spreads throughout the water column, where it reaches an equilibrium concentration. Submersed treatments are recommended on a concentration basis in parts per million (ppm) or parts per billion (ppb) and also typically require a certain exposure time to be effective. Exposure time requirements can range from hours to months depending on the herbicide, target plant, and site. Given the greater expense and potential for failure of submersed treatments, it is best to seek the advice of an aquatic specialist prior to implementing a treatment.

Specific Notes on Emergent Plant Control

Emergent plants root in the sediment, grow up through the water column, and emerge above the water surface. This strategy of “living in two worlds” often results in increased difficulty in control. Most emergent plants are treated with a foliar treatment that targets growth above water. The ratio of the above-water to below-water biomass can greatly affect herbicide efficacy. The greater the amount of biomass below water, the more difficult control is. Torpedograss and Uruguayan water primrose are two examples of this issue, as most of their total biomass is often below water. Systemic herbicides are almost always recommended for emergent plant control. Many contact herbicides may only injure emergent plant foliage. However, the plants tend to recover quickly under good growing conditions. Surfactants almost always improve herbicide efficacy on emergent plants.

Specific Notes on Algae Control

It is best to implement algae control measures before problems become severe. This is especially true for filamentous algae, which break free from the sediment and form extensive surface mats. Algae often respond positively to high nutrient levels, especially phosphorus. Incorporating best management practices to prevent nutrient runoff into ponds is one of the best long-term strategies for algae management. Copper products are often used to control algae. However, copper toxicity to fish can be a serious issue and is driven by the alkalinity of the water. In low-alkaline waters, copper toxicity is a much greater threat to fish than in high-alkaline waters. An additional option for many ponds is the use of a pond dye. Pond dyes have no algicidal activity. Instead, they reduce light penetration into the water column. They tend to work best in a preventative manner when used early in the season before algal growth becomes excessive. However, pond dyes may also reduce growth of desirable phytoplankton, which can in turn negatively influence pond productivity up the food chain.

Tables

Table 1. 

Effectiveness of fast-acting (i.e., contact) herbicides for aquatic weed control.1,2

 

Copper

Hydrogen peroxide

Diquat

Aquathol

Hydrothol

Carfentrazone

Flumioxazin

Free Floating

Duckweed(s) (Lemna sp., Spirodela sp.)

NR

NR

G-E

NR

NR

NR

E

Frog’s bit (Limnobium spongia)

NR

NR

E

NR

NR

NR

G

Giant salvinia (Salvinia molesta)

NR

NR

G

NR

NR

G

G

Mosquito fern (Azolla filiculoides)

NR

NR

E

NR

NR

E

G

Water fern (Salvinia minima)

NR

NR

E

NR

NR

E

E

Water hyacinth (Eichhornia crassipes)

F

NR

E

NR

NR

F

NR

Water lettuce (Pistia stratiotes)

F

NR

E

NR

NR

E

E

Watermeal (Wolffia columbiana)

NR

NR

NR

NR

NR

F

G-E

Floating-Leaved

Crested floating heart (Nymphoides cristata)

NR

NR

F

E

E

NR

NR

Watershield (Brasenia schreberi)

NR

NR

NR

NR

NR

NR

G

Spadderdock (Nuphar advena)

NR

NR

NR

NR

NR

NR

F

American lotus (Nelumbo lutea)

NR

NR

NR

NR

NR

NR

NR

Water lilies (Nymphaea sp.)

NR

NR

NR

NR

NR

NR

F

Submersed

Bladderwort (Utricularia sp.)

NR

NR

G

F

F

NR

G

Coontail (Ceratophyllum demersum)

NR

NR

E

E

E

NR

F

Fanwort (Cabomba caroliniana)

NR

NR

F

F

F

NR

G

Hydrilla (Hydrilla verticillata)

G

NR

E

E

E

NR

G

East Indian hygrophila (Hygrophila polysperma)

NR

NR

NR

F

NR

NR

G

Pondweed(s) (Potamogeton sp.)

G

NR

G

E

E

NR

G

Proliferating spikerush (Eleocharis baldwinii)

NR

NR

NR

NR

NR

NR

NR

Slender naiad (Najas flexilis)

G

NR

E

E

E

NR

 

Southern naiad (Najas guadalupensis)

G

NR

E

G

G

NR

F

Tape grass (Vallisneria americana)

   

F

       

Water-milfoils (Myriophyllum sp.)

NR

NR

G

G

G

NR

F

Emergent

             

Alligatorweed (Alternanthera philoxeroides)

NR

NR

NR

NR

NR

NR

F

Cattail (Typha sp.)

NR

NR

G

NR

NR

NR

NR

Dwarf rotala (Rotala rotundifolia)

NR

NR

G

NR

NR

NR

NR

Elephant ear (Xanthosoma sagittifolium)

NR

NR

NR

NR

NR

NR

NR

Parrotfeather (Myriophyllum aquaticum)

NR

NR

G

NR

NR

NR

NR

Peruvian water primrose (Ludwigia peruviana)

NR

NR

NR

NR

NR

NR

NR

Smartweed (Polygonum spp.)

NR

NR

F

NR

NR

NR

NR

Soft rush (Juncus effusus)

NR

NR

NR

NR

NR

NR

NR

Uruguayan water primrose (Ludwigia hexapetala)

NR

NR

NR

NR

NR

NR

NR

Water pennywort (Hydrocotyl spp.)

NR

NR

F

NR

NR

NR

F

Luziola (Luziola subintegra)

NR

NR

NR

NR

NR

NR

NR

Torpedograss (Panicum repens)

NR

NR

NR

NR

NR

NR

NR

Paragrass (Urochloa mutica)

NR

NR

NR

NR

NR

NR

NR

West Indian marshgrass (Hymenachne amplexicaulis)

NR

NR

NR

NR

NR

NR

NR

Wild taro (Colocasia esculenta)

NR

NR

NR

NR

NR

NR

NR

Willows (Salix sp.)

NR

NR

NR

NR

NR

NR

NR

1In general, these herbicides kill plant tissue on contact, so coverage of the weed is important for foliar applications. These herbicides are often not effective for control of plants that have extensive vegetative reproduction from lateral roots, rhizomes, or stolons.

2NR=Not recommended; F=Fair; G=Good; E=Excellent. Blank cells indicate insufficient data.

Table 2. 

Effectiveness of systemic herbicides for aquatic weed control.1

 

2,4-D granular

2,4-D liquid

Triclopyr

Bispyribac

Imazapyr2

Imazamox

Penoxsulam

Glyphosate2

Fluridone

Topramezone

Sethoxydim2

Free Floating

             

Duckweed(s) (Lemna, Spirodela spp.)

NR

F

NR

G

NR

NR

E

NR

E

NR

NR

Frog’s bit (Limnobium spongia)

NR

NR

F

 

E

E

E

NR

NR

 

NR

Giant salvinia (Salvinia molesta)

NR

NR

NR

F

NR

NR

E

E

E

F

NR

Mosquito fern (Azolla filiculoides)

NR

NR

NR

G

NR

NR

E

NR

E

 

NR

Water fern (Salvinia minima)

NR

NR

NR

G

NR

NR

E

NR

E

F

NR

Water hyacinth (Eichhornia

crassipes)

NR

E

E

G

E

E

E

G

NR

G

NR

Water lettuce (Pistia stratiotes)

NR

NR

NR

G

E

G

E

F

NR

G

NR

Watermeal (Wolffia columbiana)

NR

NR

NR

 

NR

NR

G

NR

F

 

NR

Floating-Leaved

             

Crested floating heart (Nymphoides

cristata)

NR

NR

NR

 

NR

G

   

NR

 

NR

Watershield (Brasenia schreberi)

NR

G

NR

 

E

G

NR

G

F

 

NR

Spatterdock (Nuphar advena)

E

G-E

F

 

E

E

NR

E

G

 

NR

American lotus (Nelumbo lutea)

G

G

E

 

E

E

NR

G

NR

F

NR

Water lilies (Nymphaea sp.)

E

G-E

G

 

E

E

NR

E

G

 

NR

Submersed

             

Bladderwort (Utricularia sp.)

F

NR

NR

 

NR

NR

F

NR

G

F

NR

Coontail (Ceratophyllum demersum)

G

NR

F

 

NR

NR

NR

NR

E

NR

NR

Fanwort (Cabomba caroliniana)

NR

NR

NR

 

NR

   

NR

F

 

NR

Hydrilla (Hydrilla verticillata)

NR

NR

NR

E

NR

G

E

NR

E

G

NR

East Indian hygrophila (Hygrophila

polysperma)

NR

NR

NR

NR

NR

NR

NR

NR

NR

NR

NR

Pondweed(s) (Potamogeton sp.)

NR

NR

NR

G

NR

G

E

NR

F3

E

NR

Proliferating spikerush (Eleocharis

baldwinii)

NR

NR

NR

 

NR

NR

F

NR

F

 

NR

Slender naiad (Najas flexilis)

NR

NR

NR

 

NR

NR

F

NR

E

F

NR

Southern naiad (Najas guadalupensis)

NR

NR

NR

 

NR

NR

E

NR

G

F

NR

Tape grass (Vallisneria americana)

NR

NR

NR

         

F

 

NR

Water-milfoils (Myriophyllum spp.)

E

E

E

G

NR

   

NR

E

F

NR

Emergent

             

Alligatorweed (Alternanthera

philoxeroides)

NR

F

G

G

E

E

F

G

NR

 

NR

Cattail (Typha sp.)

NR

NR

NR

 

E

E

NR

E

F

 

NR

Dwarf rotala (Rotala rotundifolia)

E

E

E

NR

NR

NR

NR

NR

NR

NR

NR

Elephant ear (Xanthosoma

sagittifolium)

NR

NR

G

 

E

E

NR

 

NR

 

NR

Parrotfeather (Myriophyllum

aquaticum)

F

E

G

G

E

F

G

NR

F

 

NR

Peruvian water primrose (Ludwigia

peruviana)

NR

F

G

 

E

G

NR

G

NR

 

NR

Smartweed(s) (Polygonum sp.)

NR

F

G

 

G

G

 

G

     

Soft rush (Juncus effusus)

F

F

NR

 

E

NR

NR

G

NR

 

NR

Uruguayan water primrose (Ludwigia

hexapetala)

NR

F

F

 

E

G

NR

G

NR

 

NR

Water pennywort (Hydrocotyl sp.)

G

G

G

G

E

E

E

E

NR

 

NR

Luziola (Luziola subintegra)

NR

NR

NR

 

E

NR

   

NR

 

G

Torpedograss (Panicum repens)

NR

NR

NR

 

E

NR

NR

G

NR

 

G

Paragrass (Urochloa mutica)

NR

NR

NR

 

E

NR

NR

G

NR

 

G

West Indian marshgrass (Hymenachne

amplexicaulis)

NR

NR

NR

 

E

NR

NR

G

NR

 

G

Wild taro (Colocasia esculenta)

NR

NR

G

 

E

E

NR

 

NR

 

NR

Willows (Salix sp.)

NR

NR

G

 

E

G

NR

G

NR

 

NR

1NR=Not recommended; F=Fair; G=Good; E=Excellent. Blank cells indicate insufficient data.

2Imazapyr, glyphosate, and sethoxydim can only be applied as foliar treatments.

3Certain species, such as Potamogeton illinoensis, are relatively tolerant to fluridone while others, such as P. nodosus, are sensitive.

Table 3. 

Effectiveness of contact herbicides for algae control.1 Currently, there are no systemic herbicides labeled for algae control.

 

Copper

Hydrogen peroxide

Diquat

Copper + Diquat

Hydrothol

Flumioxazin

Algae

Macrophytic

F

NR

NR

G

F

NR

Filamentous

G

NR

F

G

G

G

Planktonic

G

G

NR

G

NR

NR

1NR=Not recommended; F=Fair; G=Good; E=Excellent. Blank cells indicate insufficient data.

Footnotes

1.

This document is SS-AGR-44, one of a series of the Agronomy Department, UF/IFAS Extension. Original publication date September 2006. Revised February 2018. Visit the EDIS website at http://edis.ifas.ufl.edu.

2.

Original authors included T. Koschnick, former research assistant professor, Agronomy Department. Additional contributions to the current version were provided by Mike Bodle, South Florida Water Management District (retired). Revised by Stephen F. Enloe, associate professor; Michael Netherland, courtesy associate professor; William Haller, professor; and Ken Langeland, retired professor, Agronomy Department, Center for Aquatic and Invasive Plants; UF/IFAS Extension, Gainesville, FL 32611.

The use of trade names in this publication is solely for the purpose of providing specific information. UF/IFAS does not guarantee or warranty the products named, and references to them in this publication do not signify our approval to the exclusion of other products of suitable composition. Use herbicides safely. Read and follow directions on the manufacturer's label.


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.