Copper 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 Copper

Herbicide Use PatternsConsiderations
Use in Florida
  • Generally limited to waters where no other feasible control method is available
  • Primarily used by water facilities to control algae in potable water reservoirs
  • Occasional use to control floating plants near potable water intakes
  • Occasionally applied with diquat to control new, small-scale hydrilla (Hydrilla verticillata) discoveries at boat ramps where the objective is immediate eradication

Table B:  Water Uses and Functions

Water Use Parameters
Management Considerations
Downstream Uses and NeedsSee irrigation and flood control reservoir parameters below
Fish and Wildlife Mgmt. 
Vegetation plantingAvoid applications within newly installed aquatic revegetation sites
Forage and preyMay be toxic to apple snails at hydrilla application rates
Fisheries
  • May be toxic to some fish, especially trout
  • Fish toxicity generally decreases as water hardness increases
Non-game wildlifeNo issues related to this tool
Endangered speciesDiscontinued use in areas accessible by manatees
WaterfowlNo issues related to this tool; practically non-toxic to birds
Flood ControlOnly used on small scale control; no issues related to this tool
Navigation and AccessNo issues related to this tool
IrrigationNo issues related to this tool
Livestock ConsumptionNo water use restriction
Potable WaterNo water use restriction
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 Rate
  • Generally applied in combination with diquat for hydrilla control at concentration in water of 1ppm
  • Applied at rates of 0.75-1.0ppm for floating plant control near potable water intakes
Breakdown / InactivationAs an element, copper can persist indefinitely; however, it binds to particulates in water and sediments
Adsorption
  • Adsorbs to organic materials and clay particles
  • Degree of adsorption depends on acidity and alkalinity
DissipationGenerally does not disperse widely in treated waterbodies due to precipitation, settling, adsorption
Formulation 
LiquidAvailable in organic complex called copper chelate designed to keep in solution as long as possible
Solid
  • Copper sulfate available in crystal formulations; also called blue stone
  • Copper chelate available in granulated or pelletized formulations
Mode of Action
 
Contact
  • Disrupts photosynthesis
Plant Growth RegulatorUsed as herbicide for aquatic plant control applications in FWC programs
  • Functions as growth inhibitor or growth regulator at lower rates
Stewardship 
Herbicide resistance
  • Resistance reported in blue-green algae after repeated use over decades in Minnesota
  • Used occasionally for aquatic plant control in Florida and often in combination with other herbicides
Waterbody Parameters Management Considerations
Hydrology 
Water depth and volumeImportant to maintain prescribed dose; therefore, accurate bathymetry is imperative for hydrilla control
Water movement
  • Not generally an issue with aquatic plant control use patterns
  • Applied to floating plant leaves or with diquat or Aquathol for spot control at boat ramps
Water chemistry 
Dissolved oxygen (DO)
  • May be an issue for large-scale algae control in potable water reservoirs
  • Generally not an issue with the small-scale aquatic plant control use patterns in Florida
pH, alkalinity, hardness
  • In waters with less than 50ppm alkalinity, copper may be toxic to fish at rates applied to control plants
  • Copper sulfate precipitates in waters with high alkalinity (greater than 250ppm)
  • Copper precipitation less of a concern with chelated copper formulations
Nutrient content
Fast acting, but generally not an issue with the small-scale aquatic plant control use patterns in Florida
Water transparency
Sediment characteristics 
Composition  
  • Sand/Clay –  adsorption to organic particulates and clay sediments
  • Organic – adsorption to suspended organic particles
    • Avoid applying pellets to deep flocculent organic sediments
Potential for resuspensionAvoid disturbing sediments when applying to shallow waters
Plant Physiology Parameters Management Considerations
Plant origin/ growth potential 
Native
  • Used for short-term algae control
Non-native 
Invasive  
  • Used for water hyacinth or water lettuce control near potable water intakes
  • Used for small-scale or spot control of newly discovered hydrilla populations targeted for eradication
Plant growth stage (target/non-target)Shorter exposure periods may be applicable for young, actively growing plants
Plant susceptibility (target/non-target)
  • Apply to actively growing target plants
  • High rates are required to control floating plants but there are no potable water restrictions
  • Fast control when combined with diquat so used to quickly eradicate hydrilla from boat ramp areas
Potential for regrowth (target/non-target)
  • Provides long-term control of floating plants
  • Used for rapid control of new hydrilla populations before hydrilla can establish tubers
Climate Parameters Management Considerations
Weather
  • Daily
    • avoid applications during high wind and wave conditions to minimize turbidity
  • Seasonally
    • avoid large-scale applications during hot summer months
Water temperature
  • Fish toxicity increases during hot summer months, especially in waters with low alkalinity

Table D: Other Parameters

ParameterManagement Considerations
CostRelatively inexpensive, but short-term algae control
Anticipated Control Amount 
Spatial
  • Acres
    • Contact herbicide generally does not disperse
    • Acres of hydrilla controlled generally equals acres of plants to which herbicide is applied
  • Percent of water column – no issues related to this tool
Duration
  • Used to control new hydrilla populations before they become established so long-term control is expected
Time to Achieve ControlFairly fast acting for floating (few days) and submersed plants (several days)
Contractor/Equipment
  • Apply by hand-gun and airboat for small acreages of floating plants or hydrilla
  • Apply by hoses trailing from airboat for submersed plant control

Last updated: 28 November 2011