Center For Aquatic And Invasive Plants

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.

These considerations are not meant to replace or contradict the EPA approved label.
Always read and follow the pesticide label for each product used.

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
Fisheries	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
Waterfowl	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
Irrigation	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
Recreation
Boating	No issues related to this tool
Fishing	No fish consumption restriction – does not bioaccumulate in fish
Hunting	No issues related to this tool
Swimming	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	Microbial 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 Will dissipate from narrow band or small plot applications before control achieved
Formulation
Liquid	Not available in liquid formulation
Solid	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
Systemic	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
Stewardship
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
Hydrology
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
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 water body or in tank mix water
Plant Physiology Parameters	Management Considerations
Plant origin / growth potential
Native	Not used to target native plants in FWC Programs
Non-native	Not used to target non-native plants in FWC Programs
Invasive	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 Seasonally 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
Cost	No generics available Herbicides with equivalent mechanisms of action are available
Anticipated Control Amount
Spatial	Apply to entire waterbody or large blocks of hydrilla Control will likely extend beyond area to which bispyribac is directly applied
Duration	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
Contractor/Equipment	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