Skip to main content

Center for Aquatic and Invasive Plants Logo    Plant Management in Florida Waters

Center for Aquatic and Invasive Plants Logo    Plant Management in Florida Waters


*Important: See Reference Guide Beforehand

No single herbicide is appropriate for controlling all invasive aquatic plants (or nuisance growths of native aquatic plants), in all situations. A herbicide may perform differently depending on the waterbody, its use, the time of year—or even the time of day. Therefore, aquatic plant managers must have a thorough understanding of how each herbicide acts in Florida aquatic systems. The following parameters are evaluated when considering this herbicide to manage aquatic plants in a specific waterbody. Each parameter is linked to an explanation and examples are provided to demonstrate their relevance to developing comprehensive aquatic plant management strategies.

Table A: Herbicide Use Patterns for Potassium Endothall

Target PlantScientific NameUse PatternCompatible Herbicides
Hydrilla Hydrilla verticillata Frequent Potassium endothall alone
Hydrilla Hydrilla verticillata Occasional Potassium endothall applied at lower rates with bispyribac, fluridone,
penoxsulam or topramezone
Hydrilla Hydrilla verticillata Occasional Potassium endothall applied with low rates of diquat or amine endothall
for control where dissipation is anticipated (small areas or moving water)
Hydrilla Hydrilla verticillata Occasional Potassium endothall applied before systemic herbicide to reduce biomass
or after systemic herbicide applications to control remaining plants
Illinois pondweed Potamogeton illinoensis Occasional Potassium endothall applied alone or with low rate of diquat
Southern naiad Najas guadalupensis Occasional Potassium endothall applied alone with low rate of diquat
Coontail Ceratophyllum demersum Occasional Potassium endothall applied alone or with low rate of diquat
Crested floating heart Nymphoides cristata Occasional Submersed application of potassium endothall alone or potassium and
amine endothall followed by frequent spot applications of glyphosate to control regrowth

Table B: Water Uses and Functions

Water Use ParametersManagement Considerations
Downstream Uses and Needs
  • Do not apply within 600 feet of a functioning potable water intake
Fish and Wildlife Mgmt.  
Vegetation planting
  • Spotting may occur on comingled emergent plants from liquid aerial applications
Forage and prey
  • No issues related to this tool – does not bioaccumulate
  • Practically non-toxic to fish
    • Blue gill EC50 = 1,071 ppm
    • Rainbow trout EC50 = 363 ppm
Non-game wildlife
  • No issues related to this tool
Endangered species
  • No issues related to this tool
  • Non-toxic to waterfowl – mallard duck LD50 = 328 mg/kg (ppm)
Flood Control
  • No issues related to this tool
Navigation and Access
  • No issues related to this tool
  • No irrigation restrictions
Livestock Consumption
  • No issues related to this tool for applications in Florida public waters
Potable Water
  • Apply 600 feet or greater from a functioning potable water intake
  • Applications within 600 feet of potable water intake can be made if:
    • The intake is shut down until approved laboratory analysis indicates endothall below 0.1 ppm
    • Coordinate applications with water facility operator
  • No issues related to this tool
  • No fish consumption restriction – does not bioaccumulate in fish
  • No issues related to this tool
  • No swimming restriction

Table C: Herbicide, Waterbody, Plant, and Climate Parameters

Herbicide ParametersManagement Considerations
Herbicide Rate
  • Generally applied at 1-5 ppm for submersed aquatic plant control:
    • 1-3 ppm for hydrilla control
    • 3-5 ppm for coontail control
    • 3 ppm potassium endothall + 0.3 ppm amine endothall to control crested floating heart
Breakdown / Inactivation
  • Half-life is generally 3-7 days
  • Primary degradation pathway
    • Degradation rate is water-temperature and plant density dependent
  • Does not adsorb to suspended solids or sediments
  • Does not degrade by photolysis
  • Not sensitive to hydrolysis
  • Highly soluble so disperses in water
  • Higher rates may be necessary when:
    • Applying in narrow bands or small areas, or
    • Where water movement may be expected (i.e. reservoirs, canals, springs)
  • Available in liquid formulation
  • Can be used as surface or sub-surface application
    • Achieves uniform concentration throughout water column within a few hours
  • Available in solid (granular polymer) formulation
  • Granules offer good substitute where liquid potassium endothall formulation is impractical
    • Spot control of new hydrilla infestations at boat ramps or along shorelines
    • Sequential daily applications for hydrilla control in flowing water (e.g., spring runs)
    • Aerial applications among emergent plants to avoid non-target spotting
  • Disperses throughout water column in treatment zone within a few hours
Mechanism of Action
  • Unclassified in WSSA Resistance Grouping
    • Protein phosphatase inhibitor
Mode of Action  
  • Absorbed by foliage or underwater tissues
  • Interferes with protein and lipid synthesis
    • Disrupts cell membrane and respiration – cell membranes become leaky
    • Cell contents spill out – cannot make energy and die
  • Somewhat mobile in plant tissues
  • Long thought to be contact-type herbicide
  • Fast-acting
Plant Growth Regulator
  • Not used as a plant growth regulator in Florida aquatic plant control applications
Herbicide resistance
  • Not yet classified in WSSA Resistance Grouping
  • Increased tolerance identified in hydrilla at two sites in Florida
    • Potassium endothall combined with diquat effectively controlled tolerant hydrilla
  • Rotate or use with other active ingredients where appropriate
  • Compatible herbicides include: bispyribac, diquat, fluridone, penoxsulam, topramezone
Waterbody ParametersManagement Considerations
Water depth
  • Important to know water depth to calculate appropriate dose
  • Potassium endothall is used to dose water column for submersed plant control
Water volume
  • Accurate bathymetry is essential to calculate appropriate concentration
  • See label chart when applying for submersed plant control
Water movement
  • Need 12-24 hours of exposure for crested floating heart or hydrilla control
  • Apply higher rates or combine with contact herbicide where water movement is anticipated
Water chemistry  
Dissolved oxygen (DO)
  • Caution when controlling large, dense hydrilla stands in warm water to avoid DO depletion
    • Particularly when combined with diquat
pH, alkalinity, hardness
  • No issues related to this tool
Nutrient content
  • Relatively fast-acting herbicide
  • Hydrilla mats generally decline in 1-3 weeks after application
  • Nutrients may be released from decomposing plants in large treatments
Water transparency
  • Hydrilla may recover more quickly in clear or shallow waters
  • May get extended submersed plant control in deep, tannic or turbid waters
    • Low light levels inhibit recovery
Sediment characteristics  
  • Sand / Clay – no issues related to this tool
  • Organic – no issues related to this tool, does not adhere to organic material
Potential for re-suspension
  • No issues related to this tool, does not adhere to organic material
Plant Physiology ParametersManagement Considerations
Plant origin / growth potential  
  • Occasionally applied to control some native submersed plants at 3-5 ppm
    • Coontail (Ceratophyllum demersum), southern naiad (Najas guadalupensis), Illinois pondweed (Potamogeton illinoensis)
  • Little to no control reported with this compound for non-native plant management in Florida

  • Crested floating heart
    • Use alone or in conjunction with amine endothall
    • Primary control method for crested floating heart
    • Follow-up applications may be necessary to control skips
      • Alone at 2 qt/acre-foot as subsurface injection
        • Apply to actively growing plants late summer (July – August)
      • Combination at 3.0 ppm with amine endothall at 0.3 ppm
        • Apply late spring through summer
  • Hydrilla
    • Most frequently used herbicide for hydrilla control
      • Used alone or with other herbicides
    • Best results when applied to young, actively growing plants in cooler water
    • Apply to control zone quickly to avoid loss from dissipation and degradation
    • Applied at 3 ppm
      • For small plots or bands of plants where some dissipation is anticipated
      • For mature plants with high carbohydrate reserves
      • In late season control when growth is slower
      • In dense plants stands and warm water
        • Where microbial degradation of endothall is more rapid
    • Applied at 2 ppm for larger control plots (>20 acres)
    • Apply in combination with other herbicides for resistance, efficacy, or cost management
      • See other herbicide considerations to determine compatibility with current conditions
      • 1 ppm endothall + 0.37 ppm diquat for rapid control in one week
      • 1 ppm + 20 ppb bispyribac or penoxsulam
      • Endothall before systemic herbicide to reduce biomass – or after to control skips
Plant growth stage (target/non-target)
  • Need actively growing plants for herbicide uptake
  • Best results for hydrilla control when applied in late winter / early spring
    • Hydrilla is actively growing, most native plants may be dormant
    • Less plant biomass and cooler water holds more oxygen to buffer plant decomposition
  • Late season large-scale hydrilla control not recommended
    • Mature hydrilla growth rate is slower; reduced herbicide uptake
    • Plants have higher biomass and carbohydrate reserves; more difficult to control
Plant susceptibility (target/non-target)
  • Effective season-long control of hydrilla and crested floating heart when applied early
  • May also control non-target native submersed plants, especially:
    • Coontail (Ceratophyllum demersum), southern naiad (Najas guadalupensis), Illinois pondweed (Potamogeton illinoensis)
Potential for regrowth (target/non-target)
  • Hydrilla regrowth to water surface depends on extent of control, water clarity and depth
    • Regrowth is slower if root crowns are killed – limited to tuber / turion sprouting
    • Coontail, Southern naiad and Illinois pondweed are controlled by endothall
      • Usually recover during the same or next growing season
Climate ParametersManagement Considerations
Weather Daily

  • Need at least 12-24 hours of exposure
  • Dependent on dose and water temperature
  • Windy conditions may increase dissipation in spot or band applications


  • Less herbicide may be required in cooler months
    • Microbial breakdown is slower so herbicide active for longer period
  • Applying to actively growing plants increases uptake
    • Increased uptake by actively growing plants in late winter / early spring
Light intensity
  • No issues related to this tool – not broken down by photolysis
Water temperature
  • Potassium endothall degradation can occur more rapidly in warmer water (>80°F)
    • Could result in reduced efficacy
  • Lower dissolved oxygen in water to buffer plant decomposition
  • Algal growth may be more active to take up nutrients released by decomposing plants

Table D: Other Parameters

ParameterManagement Considerations
  • No generics or equivalent modes of action available
Anticipated Control Amount  
  • Area of hydrilla control is similar to area to which endothall is directly applied
  • Some dissipation and control may result outside of application zone
  • Does not disperse as widely as herbicides with longer half-lives such as fluridone or penoxsulam
    • Managers exploit dissipation by applying potassium endothall in bands up to 200 feet apart
      • Herbicide blends within a few hours of application to dose entire area between bands
  • Control duration depends on initial dose and length of exposure, extent of control and water clarity
    • If root crowns are killed, regrowth is slower; from tubers, seeds, or fragments
    • Recovery is slower in tannic, turbid or deep water where light is less intense
Time to Achieve Control
  • Symptoms in 7-10 days and control in 2-3 weeks
  • Surface or sub-surface application by boat / airboat for small / moderate scale hydrilla control
    • Additional boats needed for large-scale control to achieve / sustain dose in entire control zone
  • Apply aerially by helicopter for larger acreages
back to top