Bispyribac Considerations

*Important: See Reference Guide Beforehand

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 Bispyribac

Target Plant Scientific Name Use Pattern Compatible Herbicides
Hydrilla Hydrilla verticillata Occasional Potassium endothall

Table B: Water Uses and Functions

Water Use Parameters Management Considerations
Downstream Uses and Needs
  • Systemic herbicide that requires 60-90 days of exposure for control
  • Apply to waters with limited to no outflow to avoid downstream, off-target control
Fish and Wildlife Mgmt.  
Vegetation planting
  • Avoid whole-lake or large block applications adjacent to recently planted susceptible plants
    • Especially soft-stem bulrush (Schoenoplectus tabernaemontani) and jointed spikerush (Eleocharis interstincta)
Forage and prey
  • No issues related to this tool – potential for bioaccumulation is low
  • Practically non-toxic – blue gill and rainbow trout LC50 >100 ppm
Non-game wildlife
  • No issues related to this tool
Endangered species
  • No issues related to this tool at operational rates (30-45 ppb) and strategies
  • Practically non-toxic – mallard duck, bobwhite quail LC50 >5,620 mg/kg
Flood Control
  • No issues related to this tool
Navigation and Access
  • No issues related to this tool
  • Do not use treated water to irrigate food or ornamental crops until the bispyribac level in the treated water is determined to be 1.0 ppb or less
Livestock Consumption
  • Treated water may not be used as a primary water source for livestock until the bispyribac level in the treated water is determined to be 1.0 ppb or less
Potable Water
  • No drinking water restrictions
  • No issues related to this tool
  • No fish consumption restriction – does not bioaccumulate in fish
  • No issues related to this tool
  • No swimming restriction

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

Herbicide Parameters Management Considerations
Herbicide Rate
  • Subsurface injection to control hydrilla at 30-45 ppb
  • Need 60-90 days exposure for hydrilla control
Breakdown / Inactivation
  • Half-life in water about 30 days
  • Requires 1-2 reapplications to maintain prescribed dose for 60-90 days
  • Microbial metabolism is primary degradation pathway
  • Does not bind or adsorb to soil particles
  • Not sensitive to photolysis
  • Not sensitive to hydrolysis
  • Do not apply to flowing water or to waters subject to rapid dissipation
  • Apply to entire waterbody or large-block application
    • Will dissipate from narrow band or small plot applications before control achieved
  • Not available in liquid formulation
  • Available as water-soluble powder – mix with water and apply as solution
Mechanism of Action
  • Classified in WSSA Resistance Grouping #2
    • Amino Acid Biosynthesis Inhibitor (blocks ALS enzyme)
Mode of Action  
  • Absorbed by foliar tissues and moves to areas of new growth
  • Prevents formation of essential branched chain amino acids in plants (ALS)
  • Plant cannot make proteins, enzymes, etc. and eventually starves and dies
Plant Growth Regulator
  • Not used as a plant growth regulator in Florida aquatic plant control applications
Herbicide resistance
  • Classified in WSSA Resistance Grouping #2
  • Resistance to ALS compounds confirmed in terrestrial species
  • No tolerance or resistance issues reported for bispyribac in Florida
  • Used occasionally with potassium endothall as a resistance management strategy
  • Rotate / alternate other compounds for successive large-scale hydrilla applications
Waterbody Parameters Management Considerations
Water depth
  • Important to know water depth to calculate appropriate concentration
Water volume
  • Important to have accurate bathymetry to calculate appropriate concentration
Water movement
  • Do not apply into flowing waters or waters subject to rapid dilution or dissipation
Water chemistry  
Dissolved oxygen (DO)
  • Fairly slow acting herbicide taking two months or more to achieve hydrilla control
    • Oxygen depletion due to rapid kill and decomposition is not likely
pH, alkalinity, hardness
  • No issues related to this tool
Nutrient content
  • Slow acting herbicide taking two months or more to achieve hydrilla control
    • Rapid nutrient release and subsequent algae blooms not likely
Water transparency
  • Not broken down by photolysis
  • Clearer water may accelerate plant growth, increasing uptake and control efficacy
Sediment characteristics  
  • Not bound to clays
    • May give better control in sand bottom lakes vs. organic sediments
Potential for re-suspension
  • No issues related to this tool
    • Does not adsorb to suspended material in water body or in tank mix water
Plant Physiology Parameters Management Considerations
Plant origin / growth potential  
  • Not used to target native plants in FWC Programs
  • Not used to target non-native plants in FWC Programs

  • Subsurface injection to control hydrilla at 30-45 ppb
    • Maintain concentration for 60-90 days
  • Apply 30 ppb + 1 ppm potassium endothall for hydrilla control
  • Apply to entire waterbody or large block application
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
Plant susceptibility (target/non-target)
  • Current use in Florida is for hydrilla control (occasionally Cabomba caroliniana)
  • More effective on immature and actively growing hydrilla
  • Higher rates or applications with potassium endothall may impact eel grass
  • Little to no impact on southern naiad (Najas guadalupensis) and pondweeds (Potamogeton spp.)
  • Spatter-dock (Nuphar spp.) and jointed spikerush may be susceptible
Potential for regrowth (target/non-target)
  • Longer term control when applied to actively growing immature hydrilla
  • Temporary injury reported for soft-stem bulrush in greenhouse studies
Climate Parameters Management Considerations
Weather Daily

  • Apply in relatively calm water when little to no flushing is anticipated


  • Apply in late winter / early spring
    • When hydrilla is actively growing
    • Lower carbohydrate reserves so control may be more thorough
    • Native plants may be dormant or less susceptible
    • Summer flushing rainfalls are less likely
    • Microbial breakdown activity is reduced
  • Applying to actively growing plants increases uptake
Light intensity
  • Not broken down by photolysis
  • Higher light intensity may equate to rapid plant growth and herbicide uptake
Water temperature
  • No issues related to this tool

Table D: Other Parameters

Parameter Management Considerations
  • No generics available
  • Herbicides with equivalent mechanisms of action are available
Anticipated Control Amount
  • Apply to entire waterbody or large blocks of hydrilla
  • Control will likely extend beyond area to which bispyribac is directly applied
  • Better efficacy during cooler weather – late winter or early spring
  • More herbicide uptake in actively growing hydrilla – more thorough control
  • If root crowns are controlled, regrowth is only from tubers or turions
Time to Achieve Control
  • Slow-acting systemic – may take two or more months to control target plants
  • Wettable powder must be mixed and applied as solution
  • Apply via subsurface injections by boat
  • Conduct water analysis 2-3 weeks and redoes as needed to sustain prescribed dose
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