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Center For Aquatic And Invasive Plants

Center For Aquatic And Invasive Plants

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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 Sethoxydim

Target PlantScientific NameUse PatternCompatible Herbicides
Torpedograss Panicum repens Spot or small scale foliar applications Under development
West Indian marsh grass Hymenachne amplexicaulis Spot or small scale foliar applications Under development
Paragrass Urochloa mutica Spot or small scale foliar applications Under development

Table B: Water Uses and Functions

Water Use ParametersManagement Considerations
Downstream Uses and Needs
  • No issues related to this tool.
  • Sethoxydim is applied foliarly to target plants with little entering water column
  • Any sethoxydim entering water column degrades rapidly
Fish and Wildlife Mgmt.  
Vegetation planting
  • Will likely suppress or control beneficial grasses if mixed with target grasses
  • Does not control non-grass species
Forage and prey
  • No issues related to this tool – potential for bioaccumulation is low
Fisheries
  • 96-hour LC50 range from 1.6 mg/L in carp to 32 mg/L in rainbow trout, and 100 mg/L in bluegill sunfish
Non-game wildlife
  • U.S. EPA reports that the toxicity of sethoxydim to mammals is low
    • Practically nontoxic if absorbed through the skin
    • Can cause skin and eye irritation
    • Sethoxydim is not mutagenic or carcinogenic in humans
  • Low toxicity to wildlife
  • Potential for bioconcentration in aquatic organisms is low
Endangered species
  • No issues related to this tool at operational rates and strategies
Waterfowl
  • Practically nontoxic to birds
    • Acute oral LD50 in mallard ducks > 2,510 mg/kg and in Japanese quail > 5,000 mg/kg
    • Dietary LC50 in mallard ducks and bobwhite quail > 5,620 ppm
Flood Control
  • No issues related to this tool
Navigation and Access
  • No issues related to this tool
Irrigation
  • Do not apply within 500 feet of an irrigation intake or crop growing area
    • do not use water in the immediate area where TIGR Herbicide is applied for irrigation for 30 days after application or until analytical monitoring has verified < 1 ppb in water
Livestock Consumption
  • No issues related to this tool for applications in Florida public waters
Potable Water
  • Do not use water in the immediate area where TIGR herbicide is applied for drinking for 30 days after application or until analytical monitoring has verified < 1 ppb in water
Recreation  
Boating
  • No issues related to this tool
Fishing
  • Fishing in the immediate area of application is catch and release only for the restricted period
Hunting
  • No issues related to this tool
Swimming
  • Do not use water in the immediate area where TIGR herbicide is applied for swimming for 30 days after application or until analytical monitoring has verified < 1 ppb in water

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

Herbicide ParametersManagement Considerations
Herbicide Rate
  • 40 oz/ac in 14-day sequential applications for seasonal torpedograss control
  • 3-5% v/v for spot treatments can be done with sequential applications
    • Longer retreatment intervals need to be examined
Breakdown / Inactivation
  • Degraded rapidly by microbes and photolysis
  • Half-life in the field ranges from 5 to 25 days on soils
Microbial
  • Microbial metabolism is primary degradation pathway
Adsorption
  • Weak tendency to adsorb to soil particles
Photolysis
  • Degraded rapidly through photolysis – within an hour
Hydrolysis
  • Not sensitive to hydrolysis
Dissipation
  • No issues related to this tool
    • Not used for submersed applications
    • Degrades in as little as one hour in water
Formulation  
Liquid
  • Available only in liquid formulation
  • Contains 1.5 lb active ingredient / gallon
Solid
  • Not available in solid formulation
Mechanism of Action
  • Classified in WSSA Resistance Group #1
    • Acetyl CoA carboxylase enzyme inhibitor
Mode of Action  
Systemic
  • Absorbs rapidly through leaf surfaces, transported in xylem and phloem, and accumulates in meristematic tissues
    • Leads to failure of cell membrane integrity, especially in regions of active growth
    • Results in cessation of shoot and rhizome growth, leading to necrosis and death of shoot meristems and rhizome buds, and ultimately plant death
Plant Growth Regulator
  • Not used as a plant growth regulator in Florida aquatic plant control applications
Stewardship  
Herbicide resistance
  • Group 1 herbicide – repeated use may lead to the selection of resistant biotypes
Waterbody ParametersManagement Considerations
Hydrology  
Water depth
  • Mesocosm studies indicate control is lower for torpedograss grown at a water depth of 30 cm compared to saturated conditions.
Water volume
  • No issues related to this tool – not used for submersed applications
Water movement
  • No issues related to this tool – not used for submersed applications
Water chemistry  
Dissolved oxygen (DO)
  • No issues likely related to this parameter
    • Anticipated control sites are spot, band or fringe treatments, or marshes with low DO
pH, alkalinity, hardness
  • No issues related to this tool for application or mixing water
Nutrient content
  • No issues related to this tool – primarily used for small-scale control
Water transparency
  • No issues related to this tool – applied directly to emergent leaves
Sediment characteristics  
Composition
  • Sand/Clay – no issues related to this tool
  • Organic – no issues related to this tool
Potential for re-suspension
  • Does not adsorb to suspended material
Plant Physiology ParametersManagement Considerations
Plant origin / growth potential  
Native
  • May occasionally be used to control native grasses in unwanted areas (e.g. boat ramps)
  • Does not control cattail, sedges, or other non-grass species
Non-native
  • May occasionally be used to control non-native grasses in unwanted areas
Invasive

  • Registered in Florida to provide a new mode of action for invasive grass control
    • Evaluation underway for torpedograss, paragrass and West Indian marsh grass control
  • Will evaluate control for Tropical American water grass, in ponds, lakes, swamps, riparian areas, wetlands, marshes, reservoirs, and other areas adjacent to aquatic sites
Plant growth stage (target/non-target)
  • Need actively growing plants for herbicide uptake
  • Most effective control by applying postemergence applications early in the growing season (late spring), when perennial grasses leaf out and annual grass weeds are small
Plant susceptibility (target/non-target)
  • Apply to actively growing target plants
  • Use methylated seed oil at a mixing rate of 1% volume/volume
  • Torpedograss – 2 applications sethoxydim @ 40 oz/ac broadcast or 3-5% v/v for spot control
  • For application by boat or ground equipment
    • Use a minimum of 20, up to 100 gallons of water per acre to ensure uniform coverage
      • Increased water volume if grass foliage is dense
  • Non-target co-mingled grasses will likely be suppressed or controlled
Potential for regrowth (target/non-target)
  • Seasonal control of torpedograss with sequential applications ~14 days apart
    • Longer retreatment intervals need to be evaluated
    • Sethoxydim efficacy less than glyphosate/imazapyr, but more selective for non-grass species
Climate ParametersManagement Considerations
Weather Daily

  • Apply only when the wind speed is 10 mph or less
  • Produce larger droplets to reduce drift potential
  • Rain-fast in one hour
  • Avoid wash-off from application boat or recreational boats for one hour

Seasonally

  • Apply to actively growing plants in late winter / early spring increases efficacy
Light intensity
  • Rapidly broken down by photolysis – early season applications may produce better results
Water temperature
  • No issues related to this tool – not used for submersed applications

Table D: Other Parameters

ParameterManagement Considerations
Cost
  • No generics or equivalent modes of action available
Anticipated Control Amount
Spatial
  • Area of control is confined to the area to which sethoxydim is directly applied
    • Dissipation outside of application zone is not an issue
Duration
  • Under development for torpedograss control
    • Seasonal control then regrowth in early trials
Time to Achieve Control
  • Quickly absorbed by plant foliage (rain-fast after 1 hour)
  • Actively translocated throughout grass plants
    • Accumulates in growing points of foliage and roots
    • Growth of grasses ceases in about two days
    • Obvious symptoms may take 2-4 weeks to express
  • Two or more applications, one month apart, likely needed for torpedograss control
Contractor/Equipment
  • Currently recommended for spot or small-scale handgun applications
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