Glyphosate 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 Glyphosate

Target PlantScientific NameUse PatternHerbicides
CattailTypha spp.FrequentGlyphosate
ParagrassUrochloa mutica (syn. Brachiaria mutica)FrequentGlyphosate
Napiergrass (syn. Elephant grass)Pennisetum purpureumFrequentGlyphosate
Tropical American water grass
Luziola subintegraFrequentGlyphosate
TorpedograssPanicum repensFrequentGlyphosate + imazapyr
Water hyacinthEichhornia crassipesOccasionalGlyphosate
Water lettucePistia stratiotesOccasionalGlyphosate
Alligator weedAlternanthera philoxeroidesOccasionalGlyphosate
Spatter dockNuphar lutea subsp. advenaOccasionalGlyphosate

Table B:  Water Uses and Functions

Water Use ParametersManagement Considerations
Downstream Uses and NeedsNo issues related to this tool
Fish and Wildlife Mgmt. 
Vegetation plantingAvoid applications within emergent aquatic plant revegetation sites
Forage and preyNo issues related to this tool
FisheriesNo issues related to this tool
Non-game wildlifeNo issues related to this tool
Endangered speciesNo issues related to this tool
WaterfowlNo issues related to this tool
Flood ControlNo issues related to this tool
Navigation and AccessNo issues related to this tool
IrrigationNo issues related to this tool
Livestock ConsumptionNo issues related to this tool
Potable Water
  • Do not apply within ½ mile upstream of a functioning potable water intake, or within ½ mile of static water
  • Coordinate applications with water facility operator
  • Applications within ½ 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 
BoatingNo issues related to this tool
FishingNo fishing restrictions
HuntingNo issues related to this tool
SwimmingNo swimming restrictions

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

Herbicide ParametersManagement Considerations
Herbicide RateGenerally applied at 4.5-7.5 pints per acre for emergent or floating aquatic plant control
Breakdown / InactivationHalf  life in ponds reported from 12-60 days
AdsorptionHighly adsorbed on most soils, especially soils with high organic content
MicrobialBroken down microbially, primary pathway
Photolysis
Minor breakdown pathway
Dissipation
  • Not active in water and will not kill submersed plants
  • Binds tightly with soil so runoff is low
Formulation 
LiquidThe amine salt formulations are only available in liquid formulations for use in FL
SolidNone available
Mode of Action
 
Systemic
  • Control with foliar applications
  • Translocated throughout the plants, esp. to the roots
Plant Growth RegulatorNot 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 diquat or imazapyr where possible
Waterbody Parameters Management Considerations
Hydrology 
Water depth  No issues related to this tool, used only for floating and emergent plant control
Water volumeNo issues related to this tool, used only for floating and emergent plant control
Water movementNo 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 depletion
  • Control small patches of water hyacinth even when oxygen is low to avoid subsequent large –scale problem
pH, alkalinity, hardnessNo issues related to this tool
Nutrient content
Fairly fast acting herbicide, nutrients may be released from decomposing plants in large-scale treatments
Water transparencyNo 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
Potential for resuspensionAvoid disturbing sediments in shallow water if drawing for tank mixes
Plant Physiology Parameters Management Considerations
Plant origin/ growth potential 
Native
  • Frequently used for cattail control
  • Used for controlling native and exotic grasses in navigation trails and at ramps
  • Occasionally used for controlling spatter-dock
Non-native
  • Occasionally used to control mats of alligatorweed
Invasive  
  • Frequently used for controlling paragrass, napiergrass, torpedograss, and luziola subintegra
  • Occasionally used to control water hyacinth and lettuce, especially in waters with potable water intake
    • control is slow, may take 60-90 days
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 plant
  • 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 Parameters Management Considerations
Weather
  • Daily
    • Need at least six hours of contact for maximum effectiveness
    • Avoid application in winds greater than 10 mph
  • Seasonal
    • Apply only to actively growing plants
    • No pre-emergence or soil activity
Light intensityNo issues related to this tool
Water temperatureNo issues related to this tool

Table D: Other Parameters

ParameterManagement Considerations
CostGenerics available
Anticipated Control Amount 
Spatial
Duration
  • Provides long term control for most grasses – torpedograss is an exception
Time to Achieve ControlYellowing symptoms in 2-3 days and 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 Luziola subintegra

Last updated: 28 November 2011