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Center For Aquatic And Invasive Plants

Center For Aquatic And Invasive Plants

Glyphosate Considerations

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*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 Glyphosate

Target PlantScientific NameUse PatternCompatible Herbicides
Torpedograss Panicum repens Frequent Alone or with imazapyr
Cuban club-rush Cyperus blepharoleptos Frequent Alone or with flumioxazin, Sometimes with 2,4-D
Paragrass Urochloa mutica Frequent Usually used alone
Tussocks Mixed floating masses of herbaceous plants – often mixed with woody plant species Frequent Alone or with imazapyr, Sometimes with diquat or 2,4-D
Tropical American Watergrass Luziola subintegra Frequent Usually used alone
Floating plants Water hyacinth or water hyacinth/water lettuce mix Frequent Alone or with 2,4-D
Cattail Typha spp. Frequent Alone
Primrose willow Ludwigia octovalvis / L. peruviana Common Alone or with flumioxazin, Sometimes with 2,4-D
West Indian marsh grass Hymenachne amplexicaulis Common Alone or occasionally with 2,4-D
Spatter-dock Nuphar advena Occasional Alone
Willows Salix spp. Occasional Alone or with 2,4-D

Table B: Water Uses and Functions

Water Use ParametersManagement Considerations
Downstream Uses and Needs
  • Applications made to moving bodies of water must be made heading upstream
    • Prevents concentrations of glyphosate in one area
Fish and Wildlife Mgmt.  
Vegetation planting
  • Avoid applications within emergent aquatic plant revegetation sites, especially grass species
Forage and prey
  • No issues related to this tool
Fisheries
  • Acute Toxicity bluegill (96 hr LC50) = 120 mg/L
  • Acute LC50 for rainbow trout > 2500 mg/L.
Non-game wildlife
  • Material is practically non-toxic to aquatic organisms on an acute basis
    • LC50 or EC50 is > 100 mg/L in most sensitive species tested
Endangered species
  • No issues related to this tool
Waterfowl
  • Practically non-toxic to birds on an acute basis – LD50 > 2,000 mg/kg
  • Oral LD50, Bobwhite quail > 3,800 mg/kg
Flood Control
  • No issues related to this tool
Navigation and Access
  • No issues related to this tool
Irrigation
  • No irrigation restrictions on the use of treated water
Livestock Consumption
  • No livestock watering restrictions
Potable Water
  • Do not apply within ½ mile upstream of a functioning potable water intake, or
    • Within 1/2 mile of a functioning potable water intake in static water
  • Coordinate applications with water facility operator
  • Applications within 1/2 mile of potable water intake can be made if:
    • The intake is shut down for 48 hours, or
    • An approved laboratory analysis indicates the glyphosate concentration is below 0.7ppm
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 ParametersManagement Considerations
Herbicide Rate
  • 0.5 mg/L – not applied to water; only to foliage of emergent vegetation
  • Maximum 7.5 pt / ac
Breakdown / Inactivation
  • Half-life in ponds reported from 12-60 days
Microbial
  • Broken down microbially, primary pathway
Adsorption
  • Highly adsorbed on most soils, especially soils with high organic content
Photolysis
  • Minor breakdown pathway
Hydrolysis
  • Not sensitive to hydrolysis
Dissipation
  • Not active in water and will not kill submersed plants
  • Binds tightly with soil so runoff is low
Formulation  
Liquid
  • Available in liquid formulation only
Solid
  • Not available in solid formulation
Mechanism of Action
  • Classified in WSSA Resistance Grouping #9
    • Enzyme inhibitor – (Enolpyruvyl Shikimate-3-Phosphate (EPSP) Synthase Inhibitor)
Mode of Action  
Systemic
  • Absorbed by foliar tissues only
  • Moves to areas of new growth
  • Prevents formation of essential aromatic amino acids in plants
    • 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 used as a plant growth regulator
Stewardship  
Herbicide resistance
  • Resistance issues reported in terrestrial applications
  • No examples of resistance reported in FL aquatic use patterns
  • Rotate or use with another active ingredient where appropriate
Waterbody ParametersManagement 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
  • Dissipation not an issue related to this tool
    • Used only for floating and emergent plant control
    • Applied directly to above-water leaves or stems
Water chemistry  
Dissolved oxygen (DO)
  • Use caution for larger applications to control plants in warm water to avoid DO depletion
pH, alkalinity, hardness
  • No issues related to this tool
Nutrient content
  • No issues related to this tool
Water transparency
  • No issues related to this tool
Sediment characteristics  
Composition
  • Sand/Clay – no issues related to this tool, applied only to leaves of floating or emergent plants
  • Organic – no issues related to this tool, applied only to leaves of floating or emergent plants
  • No pre-emergence or soil activity
Potential for re-suspension
  • Avoid disturbing sediments in shallow water if drawing for tank mixes
Plant Physiology ParametersManagement Considerations
Plant origin / growth potential  
Native
  • Cattail, willow, tussocks
    • Applied at 7.5 pt / ac
    • Used for spot or large-scale control
    • Rotational or combinational tool with imazamox, imazapyr, or 2,4-D
  • Spatter-dock
    • Applied at 7.5 pt /ac
    • Used with tryclopyr and 2,4-D
Non-native
  • Primrose willow
    • Applied at 7.5 pt /ac
Invasive

  • Torpedograss, Cuban club-rush, paragrass, tropical American watergrass, West Indian marsh grass
    • Applied at 7.5 pt /ac alone or 6 pt + 2 pt imazapyr
  • Floating plants (water hyacinth / water lettuce)
Plant growth stage (target/non-target)
  • Lower rates may be applicable for young actively growing plants
Plant susceptibility (target/non-target)
  • Apply to actively growing target plants
  • No activity on submersed plants
  • Good efficacy for cattail and most grasses
    • Control is relatively fast and long duration
  • Not as effective controlling torpedograss in standing water
    • Increase effectiveness by combining with imazapyr
    • Minimize non-target effects by altering dose, timing, or use alternative herbicide
  • Toxic to most grasses – avoid overspray onto desirable grasses
Potential for regrowth (target/non-target)
  • Very effective for long-term control for cattail and most grasses
  • Avoid contact with comingled non-target plants, especially native grasses
Climate ParametersManagement Considerations
Weather Daily

  • Need at least six hours of contact for maximum effectiveness
  • Avoid application in winds greater than 10 mph

Seasonally

  • Apply only to actively growing plants
Light intensity
  • No issues related to this tool
Water temperature
  • No issues related to this tool – not applied directly to water

Table D: Other Parameters

ParameterManagement Considerations
Cost
  • Generics available
  • Alternative herbicides available for some plants controlled by glyphosate
Anticipated Control Amount  
Spatial
  • Controls only emergent and floating plants to which it is applied
  • No activity in submersed plants
Duration
  • Provides long term control for most grasses
    • Torpedograss is an exception
    • Glyphosate does not translocate well in plant tissues below the water surface
Time to Achieve Control
  • Yellowing symptoms in 2-3 days
  • Control in 2-3 weeks
    • Much longer for floating plants
Contractor/Equipment
  • Apply by hand gun and airboat for small acreages of floating and emergent plants
  • Apply aerially by helicopter for larger acreages of cattail, torpedograss and Tropical American watergrass
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