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 Plant Scientific Name Use Pattern Herbicides
Hydrilla Hydrilla Verticillata Frequent Fluridone alone or Fluridone plus contact-type or systemic herbicide
Duckweed Spirodela spp. Frequent Fluridone
Salvinia Salvinia spp. Frequent Fluridone
Watermeal Wolffia columbiana Frequent Fluridone
Coontail Ceratophyllum demersum Occasional Fluridone
Water lily Nymphaea odorata Occasional Fluridone

Table B: Water Uses and Functions

Water Use Parameters Management Considerations
Downstream Uses and Needs See irrigation and flood control reservoir parameters below
Fish and Wildlife Mgmt.  
Vegetation planting Avoid applications within newly planted aquatic revegetation sites
Forage and prey No issues related to this tool
Fisheries No fishing or fish consumption restrictions
Non-game wildlife No issues related to this tool
Endangered species No issues related to this tool
Waterfowl No issues related to this tool
Flood Control No issues related to this tool
Navigation and Access No issues related to this tool
Irrigation Rate dependent water use restrictions – see label for specific information
Less than 10 ppb concentration in treated water – no precautions for established tree or row crops or turf
Greater than 5 ppb – do not irrigate tobacco, tomatoes, peppers and newly seeded crops or grass
Livestock Consumption No 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 20 ppb
Coordinate all applications within 1320 feet (¼ mile) of an active potable water intake with water facility manager
Boating No issues related to this tool
Fishing Fishing – no fishing restriction – little to no bioaccumulation in fish
Hunting No issues related to this tool
Swimming No swimming restrictions

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

Herbicide Parameters Management 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 levels of susceptibility to fluridone in Florida public waters
Conduct genetic test 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 longer in clay or organic sediments
Adsorption Mildly binds to clay and organic particles
Microbial Broken down microbially – lesser pathway
Photolysis Broken down by sunlight – primary pathway
Dissipation May disperse widely throughout treated waterbody due to long half life
Liquid Available in two different liquid formulations
Pellet Available in various clay pellet formulations with reported rates of 7-30 days for peak release of herbicide from pellet
Release is generally faster in sandy soils
Release is generally faster in flowing water
Quick-release pellets applied directly to root zone of non-target eel grass (Vallisneria americana) may have unintended impacts
Mode of Action  
Systemic 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 less susceptible biotypes
Conduct genetic test prior to application to determine susceptibility of current hydrilla population
Conduct analytical monitoring using HPLC or other acceptible method during fluridone exposure period to confirm correct concentration is sustained
May require multiple applications to target area to sustain prescribed concentration
Sustain prescribed concentration until visual observations 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 potassium endothall) for hydrilla control
Control with fluridone first – follow up control of surviving patches or bands of hydrilla with potassium endothall
Control with contact-type herbicide first to reduce biomass and manage hydrilla regrowth with fluridone
Combine with systemic herbicide (primarily penoxsulam)
Reducing rates of each herbicide increases selectivity
Increases stewardship related to resistance management by applying two active ingredients
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 volume Important 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, hardness No issues related to this tool
Nutrient content
Slow acting – nutrients released from dying plants over extended period, therefore, no issue
Water transparency No issues related to this tool
Sediment characteristics  
Composition 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  
Native Used for duckweed, water lily, coontail control
Non-native Used for salvinia control
Invasive Used for hydrilla control in waters in which recent genetic test shows susceptibility from 3-15 ppb
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 / selective control of hydrilla that is geneticall confirmed as susceptible at rates of 3-15 ppb
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
Pellets may allow for longer exposure of herbicide – release herbicide through time
Avoid applying pellets at high rates directly to roots of eelgrass (Vallisneria americana)
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
Lengthy exposure results in death of standing crop and controls sprouting tubers for several months
Low dose inhibits tuber and turion production during fall winter applications
Climate Parameters Management Considerations
Weather Daily
Avoid applications during high wind and wave conditions to minimize herbicide dispersal
Hydrilla control efficacy and selectivity is greatest for fall, winter, early spring applications.
Herbicide photolysis is reduced during the winter due to shorter days and can lead to longer half-life.
Light intensity No issues related to this tool
Water temperature Do not apply aqueous formulation if strong thermocline exists

Table D: Other Parameters

Parameter Management Considerations
Cost Generics are available for some formulations.
Relative high fluridone cost per pound of active ingredient is mitigated through low use rates, long-term control, and high ratio of acres controlled vs. treated
Anticipated Control Amount  
Spatial Acres
Systemic herbicide generally disperses widely outside treatment area
Acres of hydrilla controlled can exceed acres of plants to which herbicide is directly applied
Percent of Water Column – no issues related to this tool
Duration Controls susceptible hydrilla up to 12-18 months
Time to Achieve Control Slow acting – hydrilla must be exposed to appropriate fluridone concentration for 30-90 days
Contractor/Equipment Apply by boat for small acreages of floating plants
Apply by boat or aerially by helicopter for larger acreages of submersed plants
Apply by hoses trailing from boat for submersed plant control
Back To Top