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Center for Aquatic and Invasive Plants Logo    Plant Management in Florida Waters

Center for Aquatic and Invasive Plants Logo    Plant Management in Florida Waters


*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.

Table A: Herbicide Use Patterns for Imazamox

Target PlantScientific NameUse PatternCompatible Herbicides
Cattail Typha spp. Frequent Applied alone
Uruguayan primrose willow complex Ludwigia grandiflora / hexapetala Frequent Alone or with carfentrazone
Primrose willow Ludwigia octovalvis / peruviana Common Alone or with carfentrazone
Water hyacinth Eichhornia crassipes Occasional Alone or with carfentrazone
Wild taro Colocasia esculenta Spot control Applied alone

Table B: Water Uses and Functions

Water Use ParametersManagement Considerations
Downstream Uses and Needs
  • See irrigation and potable water parameters below
Fish and Wildlife Mgmt.  
Vegetation planting
  • Avoid applications within newly planted aquatic revegetation sites
Forage and prey
  • No issues related to this tool
  • Practically non-toxic to fish
    • Fathead minnow LC50 – 96hr > 122 ppm
    • Bluegill LC50 – 96hr > 119 ppm
Non-game wildlife
  • No issues related to this tool
Endangered species
  • No issues related to this tool
  • Practically non-toxic to birds
    • Mallard duck dietary tests LC50 > 5,500 ppm
Flood Control
  • Need to minimize flow for at least 48 hours to allow good contact
Navigation and Access
  • No issues related to this tool
  • No turf irrigation restrictions
  • Wait 24 hours before irrigating crops if applied within 100 feet of intake at concentrations > 75 ppb
    • Approved for food crop irrigation after concentration drops below 75 ppb
Livestock Consumption
  • No issues related to this tool
Potable Water
  • No restrictions for applications made 1/4 mile or more from active potable water intake
  • Shut down water intake if application exceeds 50 ppb within ¼ mile of potable water intake
  • No issues related to this tool
  • No fishing restrictions
  • No issues related to this tool
  • No swimming restrictions

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

Herbicide ParametersManagement Considerations
Herbicide Rate
  • Maximum rates
    • Submersed applications – 500 ppb (173 fl oz / ac ft)
    • Foliar broadcast – 1 gpa
    • Spot applications – up to 5% by volume
  • Generally applied at:
    • 8-16 oz / ac for water hyacinth control
    • ~32 oz / ac for primrose willow and cattail control
Breakdown / Inactivation
  • Not sensitive to microbial breakdown
  • Weakly adsorbed to clay and organic particles
  • Broken down by sunlight – primary pathway
  • Not sensitive to hydrolysis
  • Soluble in water
    • May dissipate widely in submersed applications depending on water movement
    • Herbicidal activity only in areas where concentration is sufficient to control target plant
  • Available in liquid formulation
  • Available in granular formulation
  • Granular formulation used for spot and large-scale submersed plant applications
Mechanism of Action
  • Classified in WSSA Resistance Grouping #2
    • Acetolactate synthase (ALS) enzyme inhibitor
Mode of Action  
  • Quickly absorbed by leaves and shoots
  • Moves to areas of new growth
  • Shuts down plant growth almost immediately
    • Acts like contact herbicide in this regard
    • Control may take 2-6 weeks
  • Prevents the formation of essential branched chain amino acids in plants – ALS
  • Without these essential amino acids, the plant cannot make proteins, enzymes, etc.
    • Plant cannot continue growing and eventually starves and dies
Plant Growth Regulator
  • Not currently used as a plant growth regulator in FWC programs
  • Functions as growth inhibitor or growth regulator at lower rates of 50-150 ppb
    • May provide 3-6 months growth suppression at lower rates
Herbicide resistance
  • Resistance to ALS compounds confirmed in terrestrial species
    • No resistance reported in Florida aquatic plants
  • Rotate other compounds for successive control applications, or
    • Use in combination with other active ingredients
Waterbody ParametersManagement Considerations
Water depth
  • Amounts used for submersed applications are depth dependent – see label for chart
Water volume
  • Accurate bathymetry is required to calculate prescribed dose for submersed plant applications
    • Apply if possible when water level (volume) is lower
Water movement
  • Need at least 2-3 days of exposure for submersed applications
    • Similar to potassium endothall
Water chemistry  
Dissolved oxygen (DO)
  • DO sags not likely an issue with current FWC small-scale use patterns
pH, alkalinity, hardness
  • No issues related to this tool
Nutrient content
  • Slow acting herbicide so nutrient release from decomposing plants is slow
Water transparency
  • Color/tannic content – no issues related to this tool
  • Turbidity – no issues related to this tool
Sediment characteristics  
  • Sand/Clay – no issues related to this tool
  • Organic – do not apply granular formulation to flocculent organic sediments
Potential for re-suspension
  • No issues related to this tool
Plant Physiology ParametersManagement Considerations
Plant origin / growth potential  
  • Cattail
    • Applied at rates of 16-32 oz / ac with methylated seed oil adjuvant
    • Very active on cattail
      • 32 fl oz / ac for selective, but slow (~3 months) control when mixed with bulrush
      • 64 fl oz / ac for effective control of monocultures, but less selective
      • 32 fl oz / ac + 32 fl oz / ac glyphosate for excellent monoculture control, but non-selective
    • Much better selectivity than glyphosate or imazapyr alone
  • Primrose willow (Ludwigia peruviana)
    • Applied alone at 32 oz / ac
    • Combined at 32 oz / ac imazamox + 4 oz / ac carfentrazone

  • Uruguayan primrose willow complex
    • Applied foliarly alone at 32 oz / ac
      • Combined at 32 oz / ac imazamox + 4 oz / ac carfentrazone
    • Submersed application – 400 ppb for
      • Rosette growth stage or emergent plants less than 15″ tall
  • Water hyacinth
    • Applied foliarly at 8-16 oz / ac
    • May take 2-4 weeks for control
  • Wild taro
    • Extremely active on wild taro
    • Applied at 96-128 oz / ac
Plant growth stage (target/non-target)
  • Lower rates may have greater impact on young actively growing plants
Plant susceptibility (target/non-target)
  • Must be applied to actively growing target plants
Potential for regrowth (target/non-target)
  • May provide more than 1-year control of floating plants during in-water applications
Climate ParametersManagement Considerations
Weather Daily

  • Apply when wind / wave action is calm for submersed applications


  • Apply to actively growing plants
Light intensity
  • Intense sunlight may accelerate photolytic breakdown
Water temperature
  • Apply with water temperature generally above 50º F to ensure active growth of target plants
  • Plants must be actively growing to take up herbicide

Table D: Other Parameters

ParameterManagement Considerations
  • Generics are not available
Anticipated Control Amount  
  • Submersed applications will disperse outside treatment area depending on water movement
  • Minimize dispersal for submersed applications using granular formulations
Time to Achieve Control
  • Relatively slow acting
    • Growth ceases almost immediately after application
    • Symptoms are slow to express
    • Control may take 2-6 weeks
  • Apply by hand gun and airboat for small acreages
  • Or by helicopter for larger acreages of floating and emergent plants
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