2,4-D 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 2,4-D

  • Widespread use of liquid formulations to control water hyacinth – used alone or in combination with diquat
  • Occasional use of granular formulations for water lily control

Table B:  Water Uses and Functions

Water Use Parameters Management Considerations
Downstream Uses and Needs See irrigation
Fish and Wildlife Mgmt.  
Vegetation planting Avoid applications within newly installed aquatic plant revegetation sites
Forage and prey No issues related to this tool
Fisheries No issues related to this tool used at rates for floating plant control in Florida waters
Non-game wildlife No issues related to this tool
Endangered species No issues related to this tool
Waterfowl No issues related to this tool
Flood Control No issues related to this tool
Navigation and Access No issues related to this tool
Irrigation Do not irrigate with treated water:
  • If applied within 600 feet of functioning water intake
  • Until 7 days after application within 600 feet of irrigation water intake, or
  • An approved assay of water taken 3 days after application demonstrates a 2,4-D concentration of 0.1ppm or less
Livestock Consumption 1 day water use restriction
Potable Water
  • Do not apply within 600 feet of a functioning potable water intake for floating plant control
  • Coordinate applications with water facility operators
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
  • Generally applied at 0.5-1.0gpa
  • Lower rates applied to younger more actively growing plants
Breakdown / Inactivation Half life in water of approximately 7-14 days
Microbial Broken down microbially – primary pathway
  • Breakdown is rapid in organic soils
Adsorption

Does not adsorb to organic or clay particles
Dissipation Low dissipation when used at rates and use patterns applied to control water hyacinth in Florida
  • Slightly soluble and rapidly taken up by plants
  • Usually applied to small patches of water hyacinth
Formulation  
Liquid Only the amine salt formulations are available in liquid formulation for use in Florida waters
Solid Available in amine and ester formulations
Mode of Action
  
Contact Not a contact-type herbicide, but fast acting like contact for water hyacinth control
  • Fast acting – rapidly absorbed by plant leaves, stems and roots
  • Auxin hormone that translocates in the plant to the meristems
  • Causes uncontrolled, unsustainable growth
Plant Growth Regulator Classified as a plant growth regulator, but used as herbicide for aquatic plant control applications
Stewardship  
Herbicide resistance
  • No examples of resistance reported in Florida aquatic use patterns for water hyacinth control
  • Rotate or use in combination with diquat where possible
Waterbody Parameters  Management Considerations
Hydrology  
Water depth No issues related to this tool – used only for floating and emergent plant control
Water volume No issues related to this tool – used only for floating and emergent plant control
Water movement No issues related to this tool – used only for floating and emergent plant control
Water chemistry  
Dissolved oxygen (DO)
  • Use caution for larger applications to control plants in warm water to avoid DO sags
  • Control small patches of water hyacinth even when oxygen is low to avoid subsequent large-scale problems
pH, alkalinity, hardness No issues related to this tool
Nutrient content
  • Fast acting herbicide so may release nutrients from decomposing plants in large-scale control
Water transparency No issues related to this tool
Sediment characteristics  
Composition  
  • Sand/Clay - no issues related to this tool
  • Organic - no issues related to this tool
Potential for resuspension No issues related to this tool
Plant Physiology Parameters  Management Considerations
Plant origin/ growth potential  
Native
  • Frequently used in combination with diquat for frog’s-bit control
  • Occasionally used for controlling floating or drifting mats of pennywort and smartweed
  • Occasional control of water lilies with granular formulations
Non-native Frequently used in combination with diquat for bur-head sedge control
Invasive   Frequently used for water hyacinth control
Plant growth stage (target/non-target) Lower rates are applicable for young actively growing plants
Plant susceptibility (target/non-target)
 Apply to actively growing target plants
  • Good efficacy for water hyacinth control
  • Control is relatively fast
  • Water hyacinth usually grows among or immediately adjacent to beneficial native plants
    • Non-target exposure is often unavoidable but impacts can be minimized
    • 2,4-D does not control grasses – use 2,4-D rather than diquat when mixed with grasses
  • Minimize non-target effects by altering dose, timing, or alternative herbicide
    • 2,4-D is toxic to bulrush - use diquat to control water hyacinth mixed with bulrush
    • Curls and browns spatter-dock leaves, but quickly recovers
Potential for regrowth (target/non-target)
  • Very effective for long-term control of water hyacinth
    • Regrowth mostly from seeds and new plants
  • Comingled non-target plants may be affected
    • Use diquat to control water hyacinth growing among bulrush
    • Spatter dock quickly recovers after
Climate Parameters  Management Considerations
Weather
  • Daily
    • Highly volatile – do not apply in winds greater than 5 mph
    • Use caution applying near crops like tomatoes, peppers, grapes that are extremely susceptible to 2,4-D
  • Seasonally
    • Several months of hydrilla control when applied in fall or winter
    • Few months of control when applied to mature hydrilla in warm water
Light intensity Low intensity reduces submersed plant ability to recover
Water temperature
  • Apply with water temperature generally above 50º F to ensure active growth of target plants
  • Plants must be actively growing for plant to take up herbicide
  • Do not apply for hydrilla control if strong thermocline exists

Table D: Other Parameters

Parameter Management Considerations
Cost No generics available
Anticipated Control Amount  
Spatial
  • Acres
    • Contact-type herbicide generally does not disperse outside treatment area
    • Acres of submersed plants controlled generally equals acres of plants to which diquat (+Aquathol) is applied
    • Percent of water column – need to treat entire water column
Duration Provides good water hyacinth / water lettuce control – hydrilla control varies
Time to Achieve Control Fairly fast acting for floating (few days) and submersed (several days) plant control
Contractor/Equipment
  • Apply by hand gun and airboat for small acreages of floating plants
  • Apply aerially by helicopter for larger acreages of submersed plants
  • Apply by hoses trailing from airboat for submersed plant control, especially small acreages of hydrilla (1-200 acres)

Last updated: 13 September 2011