Fluridone Considerations

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 Fluridone

Target PlantScientific NameUse PatternHerbicides
HydrillaHydrilla VerticillataFrequentFluridone alone or Fluridone plus contact-type or systemic herbicide
DuckweedSpirodela spp.FrequentFluridone
SalviniaSalvinia spp.FrequentFluridone
WatermealWolffia columbianaFrequentFluridone
CoontailCeratophyllum demersumOccasionalFluridone
Water lilyNymphaea odorataOccasionalFluridone

Table B:  Water Uses and Functions

Water Use ParametersManagement Considerations
Downstream Uses and NeedsSee irrigation and flood control reservoir parameters below
Fish and Wildlife Mgmt. 
Vegetation plantingAvoid applications within newly planted aquatic revegetation sites
Forage and preyNo issues related to this tool
FisheriesNo fishing or fish consumption restrictions
Non-game wildlifeNo issues related to this tool
Endangered speciesNo issues related to this tool
WaterfowlNo issues related to this tool
Flood ControlNo issues related to this tool
Navigation and AccessNo issues related to this tool
IrrigationRate dependent water use restrictions – see label for specific information
  • Less than 10ppb concentration in treated water – no restriction for established tree or row crops or turf
  • Greater than 5ppb – do not irrigate tobacco, tomatoes, peppers and newly seeded crops or grass
Livestock ConsumptionNo water use restriction
Potable Water
  • Do not apply at concentration exceeding 20 parts per billion (ppb) within 1320 feet (¼ mile) from functioning potable water intake
  • No restrictions when applying fluridone at less than 20ppb
  • Coordinate all applications within 1320 feet (¼ mile) of an active potable water intake with water facility manager
BoatingNo issues related to this tool
FishingFishing – no fishing restriction – little to no bioaccumulation in fish
HuntingNo issues related to this tool
SwimmingNo swimming restrictions

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

Herbicide ParametersManagement Considerations
Herbicide Rate
  • Generally applied for hydrilla control at concentration in water of 5-18 ppb
  • Label allows rates up 150ppb – water and crop tolerance established by EPA at 150 ppb
  • Hydrilla exhibits different tolerances to fluridone in Florida public waters
    • Conduct bioassay to determine effective rate needed for each waterbody
Breakdown / Inactivation
  • Half life in water of 20 days or more
  • Varies with light intensity
  • Half life much longer in clay or organic sediments
AdsorptionMildly binds to clay and organic particles
MicrobialBroken down microbially – lesser pathway
Broken down by sunlight – primary pathway
DissipationMay disperse widely throughout treated waterbody due to long half life
LiquidAvailable in aqueous suspension and liquid formulation
PelletAvailable in various clay pellet formulations with reported rates of 0-50 days for release of herbicide from pellet
  • Release is generally faster in sandy soils
  • Release is generally faster in flowing water
  • Pellets applied to root zone of non-target plants may increase unintended impacts
Mode of Action
  • Inhibits phytoene desaturase, which leads to decreased levels of carotenes, which in turn leads to decreases in chlorophylls, photosynthesis, and carbohydrate stores
  • Slow acting – concentration must be maintained from 30-90 days
Plant Growth Regulator
  • Occasionally used as plant growth regulator
  • Low dose fall applications (5ppb) suppress tuber and turion production in hydrilla
Herbicide resistance
  • Resistance confirmed in hydrilla in Florida
    • Repeated use killed susceptible clones and selected for more fluridone-tolerant biotypes
  • Conduct bioassay prior to application to determine susceptibility of current hydrilla population
  • Conduct immunoassay during fluridone exposure period to confirm correct concentration is sustained
    • May require multiple fluridone applications to control site to sustain prescribed concentration
  • Conduct post application assays to determine phytoene levels and correlate with plant senescence
    • Sustain prescribed concentration until post application assays confirm that hydrilla will not recover
  • Rotate other compounds for subsequent hydrilla control operations or use in combination with other herbicide active ingredient
  • Used in combination with contact-type herbicides (primarily Aquathol) for hydrilla control
    • Control with fluridone first - follow up control of surviving patches or bands of hydrilla with Aquathol
    • Control with contact-type herbicide first to reduce biomass and manage hydrilla regrowth with fluridone
    • Combine with systemic herbicide (primarily penoxsulam)
Microbial degradation
  • Generally a lesser degredation pathway
  • Enhanced microbial degradation confirmed in two Florida lakes
    • Each received sequential applications over multiple years for hydrilla control
    • Half life declined to 7-10 days – too short to sustain cost-effective concentration for hydrilla control
Waterbody Parameters Management Considerations
Water depth  and volumeImportant to maintain prescribed dose; therefore, accurate bathymetry is imperative for hydrilla and other submersed plant controlcontrol
Water movement
  • Maintaining a prescribed dose of up to 90 days or more may be required for submersed plant (hydrilla) control - shorter for young actively growing plants - longer for mature, robust plants
Water chemistry 
Dissolved oxygen (DO)
  • Very slow acting for hydrilla control; therefore, dissolved oxygen sags are usually not an issue
  • Use caution for larger applications to control submersed plants in warm water to avoid DO sags
pH, alkalinity, hardnessNo issues related to this tool
Nutrient content
Slow acting – nutrients released from dying plants over extended period, therefore, no issue
Water transparency
  • Color/tannic content – no issues related to this tool
  • Turbidity – avoid applications to highly turbid waters - adheres to organic particles
Sediment characteristics 
  • Sand/Clay – slight absorption in deep flocculent clay sediments
  • Organic –slight absorption to suspended organic particles
Potential for resuspension
No issues related to this tool
Plant Physiology Parameters Management Considerations
Plant origin/ growth potential 
NativeUsed for duckweed, water lily, coontail control
Non-nativeUsed for salvinia control
Invasive  Used for hydrilla control in waters in which recent bioassay shows susceptibility from 3-15ppb
Plant growth stage (target/non-target)Shorter exposure periods may be applicable for young actively growing plants 
Plant susceptibility (target/non-target)
  • Apply to actively growing target plants – resistance confirmed in hydrilla
  • Cost-effective and selective control of hydrilla that is assayed susceptible at rates of 3-15ppb
  • Selectivity varies widely depending on:
    • Growth stage
      • Surface matted hydrilla is more difficult to control – slower growth rate, so lower herbicide uptake
      • Mature hydrilla is more difficult to control than young plants due to higher carbohydrate reserves
    • Herbicide dose
      • Test for and monitor to maintain the lowest effective dose for hydrilla control
      • Spatterdock (Nuphar lutea subspecies Advena) and pondweeds (Potamogeton spp.) are susceptible to fluridone at most rates applied to control hydrilla – expect injury
    • Formulation
      • Pellets may allow for longer exposure of herbicide – release herbicide through time
      • Avoid applying pellets directly to roots of eelgrass (Vallisneria americana) or Illinois pondweed (Potamogeton illinoensis)
    • Time of year
      • Native plants are generally dormant during fall and winter applications increasing selectivity
Potential for regrowth (target/non-target)
  • Provides long-term control of susceptible hydrilla – up to 12-18 months
Climate Parameters Management Considerations
Light intensityNo issues related to this tool
Water temperatureDo not apply aqueous formulation if strong thermocline exists

Table D: Other Parameters

ParameterManagement Considerations
  • Generics available for aqueous formulation only
  • Relative high fluridone cost is mitigated through long term control and high ratio of acres controlled vs. treated
Anticipated Control Amount 
  • Acres
    • Systemic herbicide generally disperses widely outside treatment area
    • Acres of hydrilla controlled generally exceeds acres of plants to which herbicide is applied
  • Percent of Water Column – no issues related to this tool
DurationControls susceptible hydrilla up to 12-18 months
Time to Achieve ControlSlow acting – hydrilla must be exposed to appropriate fluridone concentration for 30-90
  • Apply by hand gun and airboat for small acreages of floating plants
  • Apply aerially by helicopter for larger acreages of submersed plants
  • Apply by hoses trailing from airboat for submersed plant control

Last updated: 22 July 2014