Topramezone Considerations

No single herbicide is appropriate for controlling all invasive aquatic plants (or nuisance growths of native aquatic plants), in all situations. An 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 Topramezone

Target Plant Scientific Name Use Pattern Compatible Herbicides
Hydrilla Hydrilla verticillata Operational Topramezone alone for large-scale hydrilla control in quiescent waters. Other uses of this newly registered herbicide are under evaluation.

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 installed revegetation sites.
Forage and prey No issues related to this tool
Fisheries Practically non-toxic – rainbow trout LC50 >96 hr. >97.4 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

  • Used alone, topramezone requires extensive contact time of 60-120 or more days for submersed plant control
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.

No turf irrigation restrictions for topramezone concentration <30 ppb

Livestock Consumption No issues related to this tool
Potable Water Do not use when concentration exceeds 45 ppb
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

Apply topramezone to control hydrilla at 25-40 ppb based on site and level of 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 and extended period in water column
  • Herbicide activity only in areas where concentration is sufficient to control target plant
Formulation  
Liquid Not available in liquid formulation
   
Mode of Action
 Inhibits 4-HPPD enzyme; impacts chlorophyll synthesis
Systemic
  • Slow acting – absorbed by leaves, shoots, and roots
  • Translocated to meristematic tissue and inhibits chlorophyll synthesis
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
  • Rotate / alternate 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
  • Does not adsorb to suspended material in tank mix water
Plant Physiology Parameters  Management Considerations
Plant origin/ growth potential  
Native Control of native species under evaluation – no use patterns at this time
Non-native Control of non-native species under evaluation – no use patterns at this time
Invasive  

Operational use for whole-lake or large-scale hydrilla control

Controls water hyacinth via root uptake during hydrilla control – operational use under evaluation

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 FL is for hydrilla control only
    • More effective on immature and actively growing hydrilla
  • Topramezone rates of 25-40 ppb depending on site and level of plant maturity
  • 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 such as 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
  • Seasonally
    • Apply in late winter / early spring when hydrilla is actively growing and generally has lower carbohydrate reserves; therefore, control may be more thorough
    • Apply to flow-through reservoirs during drier periods when flushing rainfalls are 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 temperatures are generally above 50o F to ensure active hydrilla growth

Table D: Other Parameters

Parameter Management Considerations
Cost No generics available
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 annual hydrilla control (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