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 Plant	Scientific Name	Use Pattern	Compatible Herbicides
Hydrilla	Hydrilla verticillata	Occasional
Newly registered compound for Florida waters - control of other species under evaluation

Table B: Water Uses and Functions

Water Use Parameters	Management Considerations
Downstream Uses and Needs	Systemic herbicide - apply to waters with limited to no outflow
Fish and Wildlife Mgmt.
Vegetation planting	Avoid whole-lake or large block applications to hydrilla adjacent to recently planted susceptible plants, especially soft stem bulrush and jointed spikerush
Forage and prey	No issues related to this tool
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
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 I.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 I.0 ppb or less
Potable Water	No drinking water restrictions
Recreation
Boating	No issues related to this tool
Fishing	No fish consumption restriction
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 Maintain concentration for 60-90 days Apply to entire waterbody or large block application
Breakdown / Inactivation	Half-life in water about 30 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
Formulation
Liquid	Not available in liquid formulation
Solid	Available 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 Regulator	Not 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 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 up to two months 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	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	Sand/Clay - no issues related to this tool Organic - no issues related to this tool
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
Native	Newly registered - control of otherspecies under evaluation
Non-native	Newly registered - control of otherspecies under evaluation
Invasive	Developing use patterns to selectively control hydrilla among native naiad and pondweed
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 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 temperature	No issues related to this tool

Table D: Other Parameters

Parameter	Management Considerations
Cost	No 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 Control	Slow-acting systemic - may take two or more months to control target plants
Contractor/Equipment	Apply via subsurface injections by boat

Last updated: 18 October 2011

Plant Management in Florida Waters : An Integrated Approach