Center For Aquatic And Invasive Plants

Topramezone 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 Topramezone

Target Plant	Scientific Name	Use Pattern	Compatible Herbicides
Hydrilla	Hydrilla verticillata	Occasional	Alone or with potassium endothall
Water hyacinth	Eichhornia crassipes	Under Evaluation	Alone

Table B: Water Uses and Functions

Water Use Parameters	Management Considerations
Downstream Uses and Needs	No crop tolerances established except for corn
Fish and Wildlife Mgmt.
Vegetation planting	Avoid applications to hydrilla within or adjacent to newly planted revegetation sites
Forage and prey	No issues related to this tool
Fisheries	Practically non-toxic Rainbow trout LC₅₀ – 96 hr. > 97.4 ppm Bluegill LC₅₀ > 239 ppm
Non-game wildlife	No issues related to this tool
Endangered species	No issues related to this tool
Waterfowl	Practically non-toxic Mallard duck LC₅₀ > 5,000 mg/kg
Flood Control	May be difficult to maintain effective concentration in flow-through flood control waters Topramezone requires contact time of 60-120 days for submersed plant control Combine with potassium endothall to reduce exposure period
Navigation and Access	No issues related to this tool
Irrigation	No crop tolerance established except for corn Do not apply to waters used for food crop irrigation until concentration drops below 1 ppb Except for corn (up to 25 ppb) No irrigation restrictions for established turf with topramezone concentration < 30 ppb Do not use for irrigation of sod farms, golf course greens and tees, or newly seeded turf If > 1 ppb, without manufacturer approval
Livestock Consumption	No livestock consumption restrictions
Potable Water	Do not use when concentration exceeds 45 ppb
Recreation
Boating	No issues related to this tool
Fishing	No fish consumption restrictions
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	Maximum rate 50 ppb Generally applied at 25-40 ppb for hydrilla control Depending on growth stage and plant maturity
Breakdown / Inactivation	Average half-life in Florida waters is about 4-6 weeks
Microbial	Minor breakdown pathway via aerobic processes
Adsorption	Weakly adsorbed to soil and organic particles
Photolysis	Primary breakdown pathway via sunlight
Hydrolysis	Not sensitive to hydrolysis
Dissipation	May dissipate widely due to long exposure requirements Herbicide activity only in areas where concentration is sufficient to control target plant
Formulation
Liquid	Not available in liquid formulation
Solid	Available in wettable powder
Mechanism of Action	Classified in WSSA Resistance Grouping #27 Chemical class called pyrazolones Inhibits 4-HPPD enzyme (4-Hydroxy-phenyl-pyruvate-dioxygenase) Impacts chlorophyll synthesis
Mode of Action
Systemic	Slow acting – absorbed by leaves, shoots, and roots Translocated to meristematic tissue and inhibits chlorophyll synthesis via oxidation Results in bleaching symptoms of the growing shoot tissue (white or pink coloration) Subsequent death of the above ground portion of the pant
Plant Growth Regulator	Not used as a plant growth regulator in Florida aquatic plant control applications
Stewardship
Herbicide resistance	Isolated resistance to 4-HPPD compounds confirmed in terrestrial species No evidence of resistance in Florida aquatic plants Rotate or combine with other compounds for successive large-scale applications
Waterbody Parameters	Management Considerations
Hydrology
Water depth	Amounts used are depth-dependent for submersed plant control See label for chart calculations
Water volume	Accurate bathymetry required to calculate appropriate concentration Apply if possible when water level (volume) is lower to reduce amount of required herbicide
Water movement	Needs several months of exposure to control established hydrilla Limited to use in waters with good retention capability Under evaluation for shorter exposure requirements for herbicide combination use patterns
Water chemistry
Dissolved oxygen (DO)	Slow acting herbicide taking several 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 several months to achieve hydrilla control Rapid nutrient release and subsequent algae blooms not likely
Water transparency	Broken down by photolysis – heavily tannin-stained waters may prolong half-life Clearer water may accelerate plant growth, increasing control efficacy
Sediment characteristics
Composition	Not bound to clays or organics
Potential for re-suspension	Not bound to clays or organics
Plant Physiology Parameters	Management Considerations
Plant origin / growth potential
Native	No current use patterns to control native aquatic plants in FWC-funded programs
Non-native	No current use patterns to control non-native aquatic plants in FWC-funded programs
Invasive	Hydrilla Operational use for whole-lake or large-scale hydrilla control Rates of 25-40 ppb depending on site and level of plant maturity Monitor in-water concentration and apply bump application to sustain prescribed dose Water hyacinth Controls water hyacinth via root uptake during hydrilla control Operational use under evaluation for foliar or submersed applications
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 Lower rates may be applicable for young actively growing plants
Plant susceptibility (target/non-target)	Current use pattern in Florida is for hydrilla control only More effective on immature and actively growing hydrilla Higher rates may be necessary to control mature hydrilla or in warmer waters
Potential for regrowth (target/non-target)	Longer term control when applied to actively growing immature hydrilla Seasonal control of some native submersed plants e.g., Illinois pondweed (Potamogeton illinoensis) May temporarily impact American lotus (Nelumbo americana) Minimize native plant impacts by applying when native plants are dormant
Climate Parameters	Management Considerations
Weather	Daily Apply when wave action is low to minimize dissipation Seasonally Apply in late winter / early spring for hydrilla control Hydrilla is actively growing and generally has lower carbohydrate reserves Control may be more thorough Apply to flow-through reservoirs during drier periods when flushing rainfall is less likely
Light intensity	Broken down by photolysis – higher light intensity may accelerate breakdown Lower light intensity may prolong half-life and inhibit hydrilla ‘s ability to regrow and recover
Water temperature	Apply when water temperature is generally above 50°F to ensure active hydrilla growth

Table D: Other Parameters

Parameter	Management Considerations
Cost	No generics available Other herbicides available with similar systemic use pattern for hydrilla control
Anticipated Control Amount
Spatial	Systemic herbicide requiring 60-120 days of contact for hydrilla control Apply to entire waterbody or large block of hydrilla in protected waters
Duration	Provides hydrilla control for ~12 months when applied alone with several months of exposure 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 60-120+ days to control target plants
Contractor/Equipment	Apply via subsurface injections by boat