Center For Aquatic And Invasive Plants

Sethoxydim Considerations

*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.

These considerations are not meant to replace or contradict the EPA approved label.
Always read and follow the pesticide label for each product used.

Table A: Herbicide Use Patterns for Sethoxydim

Target Plant	Scientific Name	Use Pattern	Compatible 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 Parameters	Management 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 Parameters	Management 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 Parameters	Management 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 Parameters	Management 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 Parameters	Management 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

Parameter	Management 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