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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 Topramezone

Target PlantScientific NameUse PatternCompatible Herbicides
Hydrilla Hydrilla verticillata Occasional Alone or with potassium endothall
Water hyacinth Eichhornia crassipes Under Evaluation Alone

Table B: Water Uses and Functions

Water Use ParametersManagement Considerations
Downstream Uses and Needs
  • No crop tolerances established except for corn
Fish and Wildlife Mgmt.  
Vegetation planting
  • Avoid applications to hydrilla within or adjacent to newly planted revegetation sites
Forage and prey
  • No issues related to this tool
  • Practically non-toxic
    • Rainbow trout LC50 – 96 hr. > 97.4 ppm
    • Bluegill LC50 > 239 ppm
Non-game wildlife
  • No issues related to this tool
Endangered species
  • No issues related to this tool
  • Practically non-toxic
    • Mallard duck LC50 > 5,000 mg/kg
Flood Control
  • May be difficult to maintain effective concentration in flow-through flood control waters
    • Topramezone requires contact time of 60-120 days for submersed plant control
    • Combine with potassium endothall to reduce exposure period
Navigation and Access
  • No issues related to this tool
  • No crop tolerance established except for corn
  • Do not apply to waters used for food crop irrigation until concentration drops below 1 ppb
    • Except for corn (up to 25 ppb)
  • No irrigation restrictions for established turf with topramezone concentration < 30 ppb
  • Do not use for irrigation of sod farms, golf course greens and tees, or newly seeded turf
    • If > 1 ppb, without manufacturer approval
Livestock Consumption
  • No livestock consumption restrictions
Potable Water
  • Do not use when concentration exceeds 45 ppb
  • No issues related to this tool
  • No fish consumption restrictions
  • No issues related to this tool
  • No swimming restrictions

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

Herbicide ParametersManagement Considerations
Herbicide Rate
  • Maximum rate 50 ppb
  • Generally applied at 25-40 ppb for hydrilla control
    • Depending on growth stage and plant maturity
Breakdown / Inactivation
  • Average half-life in Florida waters is about 4-6 weeks
  • Minor breakdown pathway via aerobic processes
  • Weakly adsorbed to soil and organic particles
  • Primary breakdown pathway via sunlight
  • Not sensitive to hydrolysis
  • May dissipate widely due to long exposure requirements
  • Herbicide activity only in areas where concentration is sufficient to control target plant
  • Not available in liquid formulation
  • Available in wettable powder
Mechanism of Action
  • Classified in WSSA Resistance Grouping #27
    • Chemical class called pyrazolones
    • Inhibits 4-HPPD enzyme (4-Hydroxy-phenyl-pyruvate-dioxygenase)
    • Impacts chlorophyll synthesis
Mode of Action  
  • Slow acting – absorbed by leaves, shoots, and roots
  • Translocated to meristematic tissue and inhibits chlorophyll synthesis via oxidation
    • Results in bleaching symptoms of the growing shoot tissue (white or pink coloration)
    • Subsequent death of the above ground portion of the pant
Plant Growth Regulator
  • Not used as a plant growth regulator in Florida aquatic plant control applications
Herbicide resistance
  • Isolated resistance to 4-HPPD compounds confirmed in terrestrial species
  • No evidence of resistance in Florida aquatic plants
  • Rotate or combine with other compounds for successive large-scale applications
Waterbody ParametersManagement Considerations
Water depth
  • Amounts used are depth-dependent for submersed plant control
    • See label for chart calculations
Water volume
  • Accurate bathymetry required to calculate appropriate concentration
  • Apply if possible when water level (volume) is lower to reduce amount of required herbicide
Water movement
  • Needs several months of exposure to control established hydrilla
    • Limited to use in waters with good retention capability
    • Under evaluation for shorter exposure requirements for herbicide combination use patterns
Water chemistry  
Dissolved oxygen (DO)
  • Slow acting herbicide taking several months to achieve hydrilla control
  • Oxygen depletion due to rapid kill and decomposition is not likely
pH, alkalinity, hardness
  • No issues related to this tool
Nutrient content
  • Fairly slow acting herbicide taking several months to achieve hydrilla control
    • Rapid nutrient release and subsequent algae blooms not likely
Water transparency
  • Broken down by photolysis – heavily tannin-stained waters may prolong half-life
  • Clearer water may accelerate plant growth, increasing control efficacy
Sediment characteristics  
  • Not bound to clays or organics
Potential for re-suspension
  • Not bound to clays or organics
Plant Physiology ParametersManagement Considerations
Plant origin / growth potential  
  • No current use patterns to control native aquatic plants in FWC-funded programs
  • No current use patterns to control non-native aquatic plants in FWC-funded programs

  • Hydrilla
    • Operational use for whole-lake or large-scale hydrilla control
    • Rates of 25-40 ppb depending on site and level of plant maturity
    • Monitor in-water concentration and apply bump application to sustain prescribed dose
  • Water hyacinth
    • Controls water hyacinth via root uptake during hydrilla control
    • Operational use under evaluation for foliar or submersed applications
Plant growth stage (target/non-target)
  • Need actively growing plants for herbicide uptake
  • For best results, apply in late winter / early spring before hydrilla matures
  • Lower rates may be applicable for young actively growing plants
Plant susceptibility (target/non-target)
  • Current use pattern in Florida is for hydrilla control only
  • More effective on immature and actively growing hydrilla
  • Higher rates may be necessary to control mature hydrilla or in warmer waters
Potential for regrowth (target/non-target)
  • Longer term control when applied to actively growing immature hydrilla
  • Seasonal control of some native submersed plants
    • e.g., Illinois pondweed (Potamogeton illinoensis)
    • May temporarily impact American lotus (Nelumbo americana)
    • Minimize native plant impacts by applying when native plants are dormant
Climate ParametersManagement Considerations
Weather Daily

  • Apply when wave action is low to minimize dissipation


  • Apply in late winter / early spring for hydrilla control
  • Hydrilla is actively growing and generally has lower carbohydrate reserves
    • Control may be more thorough
  • Apply to flow-through reservoirs during drier periods when flushing rainfall is less likely
Light intensity
  • Broken down by photolysis – higher light intensity may accelerate breakdown
  • Lower light intensity may prolong half-life and inhibit hydrilla ‘s ability to regrow and recover
Water temperature
  • Apply when water temperature is generally above 50°F to ensure active hydrilla growth

Table D: Other Parameters

ParameterManagement Considerations
  • No generics available
  • Other herbicides available with similar systemic use pattern for hydrilla control
Anticipated Control Amount  
  • Systemic herbicide requiring 60-120 days of contact for hydrilla control
  • Apply to entire waterbody or large block of hydrilla in protected waters
  • Provides hydrilla control for ~12 months when applied alone with several months of exposure
  • Better efficacy during cooler weather – late winter or early spring
  • More herbicide uptake in actively growing hydrilla – more thorough control
Time to Achieve Control
  • Slow-acting systemic – may take 60-120+ days to control target plants
  • Apply via subsurface injections by boat
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