Bispyribac 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 Bispyribac

Target PlantScientific NameUse PatternCompatible Herbicides
HydrillaHydrilla verticillataOperationalAlone or with potassium endothall

Table B:  Water Uses and Functions

Water Use ParametersManagement Considerations
Downstream Uses and NeedsSystemic herbicide - apply to waters with limited to no outflow
Fish and Wildlife Mgmt. 
Vegetation plantingAvoid whole-lake or large block applications to hydrilla adjacent to recently planted susceptible plants, especially soft stem bulrush and jointed spikerush
Forage and preyNo issues related to this tool
FisheriesPractically non-toxic - blue gill and rainbow trout LC50 >100 ppm
Non-game wildlifeNo issues related to this tool
Endangered speciesNo issues related to this tool
WaterfowlPractically non-toxic - mallard duck, bobwhite quail LC50 >5,620 mg/kg
Flood ControlNo issues related to this tool
Navigation and AccessNo issues related to this tool
IrrigationDo not use treated water to irrigate food or ornamental crops until the bispyribac level in the treated water is determined to be I.0  ppb or less
Livestock ConsumptionTreated water may not be used as a primary water source for livestock until the bispyribac level in the treated water is determined  to be I.0  ppb or less
Potable WaterNo drinking water restrictions
Recreation 
BoatingNo issues related to this tool
FishingNo fish consumption restriction
HuntingNo issues related to this tool
SwimmingNo swimming restriction

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

Herbicide ParametersManagement Considerations
Herbicide Rate
  • 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
Breakdown / InactivationHalf-life in water about 30 days
MicrobialMicrobial metabolism is  primary degradation pathway
Adsorption

Does not bind or adsorb to soil particles

Photolysis

Not sensitive to photolysis

Hydrolysis

Not sensitive to hydrolysis

Dissipation
  • Do not apply to flowing water or to waters subject to rapid dissipation
  • Apply to entire waterbody or large-block application
Formulation 
LiquidNot available in liquid formulation
SolidAvailable as water-soluble powder - mix with water and apply as solution
Mode of Action
 
Contact
  • Inhibits the plant enzyme acetolactate synthase (ALS)
  • Inhibits cell division and causes plant death
Plant Growth RegulatorNot used as a plant growth regulator in Florida aquatic plant control applications
Stewardship 
Herbicide resistance
  • No tolerance or resistance issues reported for bispyribac in Florida
  • Resistance to ALS compounds confirmed in terrestrial species
  • Rotate / alternate other compounds for successive large-scale applications
Waterbody Parameters Management Considerations
Hydrology 
Water depthImportant to know water depth to calculate appropriate concentration
Water volumeImportant to have accurate bathymetry to calculate appropriate concentration
Water movementDo not apply into flowing waters or waters subject to rapid dilution or dissipation
Water chemistry 
Dissolved oxygen (DO)
  • Fairly slow acting herbicide taking up to two months to achieve hydrilla control
    • Oxygen depletion due to rapid kill and decomposition is not likely
pH, alkalinity, hardnessNo issues related to this tool
Nutrient content
  • Fairly slow acting herbicide taking up to two months 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 control efficacy
Sediment characteristics 
Composition  
  • 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 tank mix water
Plant Physiology Parameters Management Considerations
Plant origin/ growth potential 
NativeControl of native species under evaluation
Non-nativeControl of non-native species under evaluation
Invasive  Control hydrilla 30-45 ppb alone or 30 ppb + 1 ppm potassium endothall 
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 pattern in FL is for hydrilla control only
    • More effective on immature and actively growing hydrilla
  • Higher rates or applications with potassium endothall may impact eel grass
  • Early results show selectivity for southern naiad and pondweeds
  • Spatter-dock (Nuphar spp.) and jointed spikerush (Eleocharis spp.) 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
  • Seasonally
    • Apply in late winter / early spring when hydrilla is actively growing
    • Lower carbohydrate reserves so control may be more thorough
Light intensity
  • Not broken down by photolysis
  • Higher light intensity may equate to rapid plant growth and herbicide uptake
Water temperatureNo issues related to this tool

Table D: Other Parameters

ParameterManagement Considerations
CostNo generics available
Anticipated Control Amount 
Spatial
  • Systemic herbicide requiring 60-90 days of contact for hydrilla control
  • Apply to entire waterbody or large block of hydrilla
Duration
  • Better efficacy during cooler weather - late winter or early spring
  • More herbicide uptake in actively growing hydrilla - more thorough control
Time to Achieve ControlSlow-acting systemic - may take two or more months to control target plants
Contractor/EquipmentApply via subsurface injections by boat

Last updated: 03 July 2014