Fluridone 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 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
Recreation  
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
Formulation  
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
Stewardship  
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
Hydrology  
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
    • Formulation
      • 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
  • Seasonal
    • 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
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