Topramezone Considerations

No single herbicide is appropriate for controlling all invasive aquatic plants (or nuisance growths of native aquatic plants), in all situations. An 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
HydrillaHydrilla verticillataOperationalTopramezone alone for large-scale hydrilla control in quiescent waters. Other uses of this newly registered herbicide are under evaluation.

Table B:  Water Uses and Functions

Water Use ParametersManagement Considerations
Downstream Uses and NeedsNo crop tolerances established except for corn
Fish and Wildlife Mgmt. 
Vegetation plantingAvoid applications to hydrilla within or adjacent to newly installed revegetation sites.
Forage and preyNo issues related to this tool
FisheriesPractically non-toxic - rainbow trout LC50 >96 hr. >97.4 ppm
Non-game wildlifeNo issues related to this tool
Endangered speciesNo issues related to this tool
WaterfowlPractically non-toxic - mallard duck LC50 >5,000 mg/kg
Flood Control

May be difficult to maintain effective concentration in flow-through flood control waters

  • Used alone, topramezone requires extensive contact time of 60-120 or more days for submersed plant control
Navigation and AccessNo 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.

No turf irrigation restrictions for topramezone concentration <30 ppb

Livestock ConsumptionNo issues related to this tool
Potable WaterDo not use when concentration exceeds 45 ppb
BoatingNo issues related to this tool
FishingNo fish consumption restriction
HuntingNo issues related to this tool
SwimmingNo swimming restriction

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

Herbicide ParametersManagement Considerations
Herbicide Rate

Apply topramezone to control hydrilla at 25-40 ppb based on site and level of plant maturity

Breakdown / InactivationAverage 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 and extended period in water column
  • Herbicide activity only in areas where concentration is sufficient to control target plant
LiquidNot available in liquid formulation
Mode of Action
 Inhibits 4-HPPD enzyme; impacts chlorophyll synthesis
  • Slow acting - absorbed by leaves, shoots, and roots
  • Translocated to meristematic tissue and inhibits chlorophyll synthesis
Plant Growth RegulatorNot used as a plant growth regulator in Florida aquatic plant control applications
Herbicide resistance
  • Isolated resistance to 4-HPPD compounds confirmed in terrestrial species
  • Rotate / alternate other compounds for successive large-scale applications
Waterbody Parameters Management Considerations
Water depthAmounts 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 movementNeeds 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, hardnessNo 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
Sediment characteristics 
  • Not bound to clays or organics
Potential for re-suspension
  • Does not adsorb to suspended material in tank mix water
Plant Physiology Parameters Management Considerations
Plant origin/ growth potential 
NativeControl of native species under evaluation - no use patterns at this time
Non-nativeControl of non-native species under evaluation - no use patterns at this time

Operational use for whole-lake or large-scale hydrilla control

Controls water hyacinth via root uptake during hydrilla control - operational use under evaluation

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 FL is for hydrilla control only
    • More effective on immature and actively growing hydrilla
  • Topramezone rates of 25-40 ppb depending on site and level of plant maturity
  • 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 such as Illinois pondweed (Potamogeton illinoensis)
  • May temporarily impact American lotus (Nelumbo americana)
  • Minimize native plant impacts by applying when native plants are dormant
Climate Parameters Management Considerations
  • Daily
    • Apply when wave action is low
  • Seasonally
    • Apply in late winter / early spring when hydrilla is actively growing and generally has lower carbohydrate reserves; therefore, control may be more thorough
    • Apply to flow-through reservoirs during drier periods when flushing rainfalls are 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 temperatureApply when water temperatures are generally above 50o F to ensure active hydrilla growth

Table D: Other Parameters

ParameterManagement Considerations
CostNo generics available
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 annual hydrilla control (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 ControlSlow-acting systemic - may take 60-120+ days to control target plants
Contractor/EquipmentApply via subsurface injections by boat

Last updated: 22 August 2014