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 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 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 20ppb 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
Breakdown / Inactivation	Half life in water of 20 days or more Varies with light intensity Half life much 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 as an aqueous suspension
Pellet	Available in various clay pellet formulations with 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
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	Herbicide resistance for hydrilla management 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 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) 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 control
Water movement	At least 24 hours of contact required for submersed plant control
Water chemistry
Dissolved oxygen (DO)	Very slow acting for hydrilla control; therefore, dissolved oxygen sags are 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	Color/tannic content – no issues related to this tool Turbidity – avoid applications to highly turbid waters
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 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 allow for longer exposure of herbicide – releases 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 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
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 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
Spatial	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
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
Contractor/Equipment	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: 28 November 2011

Plant Management in Florida Waters : An Integrated Approach