Herbicide Rate |
- Maximum label concentration for controlling hydrilla is 150 ppb per growing season
|
Breakdown / Inactivation |
- Average half-life in water of about 2-4 weeks in Florida waters
|
Microbial |
- Slow microbial breakdown – minor pathway
|
Adsorption |
- Weakly adsorbed to clay and organic particles in water
- Adsorbs to dry soils and broken down by microbes
|
Photolysis |
- Broken down primarily by sunlight in water
- Half-life 20-50 days
|
Hydrolysis |
- Not sensitive to hydrolysis
|
Dissipation |
- May dissipate widely with long exposure requirement and extended presence in water column
- Herbicidal activity only in areas where concentration is sufficient for controlling the target plant
- Combine with potassium endothall for submersed plant control in moving or open water
- Significantly reduces required exposure time to control submersed plants
|
Formulation |
|
Liquid |
- Available in liquid formulation
|
Solid |
- Available in solid formulation
|
Mechanism of Action |
- Classified in WSSA Resistance Grouping #2
- Acetolactate enzyme (ALS) inhibitor
|
Mode of Action |
|
Systemic |
- Absorbed by foliar tissues
- Moves to areas of new growth
- Prevents the formation of essential branched chain amino acids in plants – ALS
- Without these essential amino acids, the plant cannot make proteins, enzymes, etc.
- Plant cannot continue growing and eventually starves and dies
|
Plant Growth Regulator |
- Used as herbicide for aquatic plant control applications in FWC programs
- Functions as growth inhibitor or growth regulator at lower rates
|
Stewardship |
|
Herbicide resistance |
- Resistance to ALS compounds confirmed in terrestrial species
- No evidence of penoxsulam resistance in Florida waters
- Rotate with other compounds for successive large-scale applications, or
- Use in combination with another active ingredient
- Most commonly potassium endothall or fluridone for hydrilla control
- Used in combination with flumioxazin or carfentrazone for foliar applications to floating plants
|
Waterbody Parameters | Management Considerations |
Hydrology |
|
Water depth |
- Amounts used are depth dependent for submersed plant control – see label for chart
|
Water volume |
- Accurate bathymetry is required to calculate prescribed dose for submersed plant control
- Apply if possible when water level (volume) is lower
- Reduces the amount of herbicide required
|
Water movement |
- Avoid using alone for small-scale, open-water submersed plant control
- Required exposure period may be too long to sustain herbicide in the control zone
- Consider combining with potassium endothall
- Need 3-14 days of exposure for optimum submersed plant control when combined with potassium endothall
|
Water chemistry |
|
Dissolved oxygen (DO) |
- Slow acting when used alone
- When applied with potassium endothall or other contact type herbicides for submersed plant control, use caution for large control sites and in warmer water to avoid oxygen sags
- DO sags not likely an issue in fall or spring through early summer applications
|
pH, alkalinity, hardness |
- No issues related to this tool
|
Nutrient content |
- No issues related to this tool
|
Water transparency |
- Dark or tannic stained waters may decrease sunlight and prolong half-life
- Turbidity not an issue related to this tool
|
Sediment characteristics |
|
Composition |
- Sand/Clay – no issues related to this tool
- Organic – no issues related to this tool
|
Potential for re-suspension |
- No issues related to this tool
|
Plant Physiology Parameters | Management Considerations |
Plant origin / growth potential |
|
Native |
- Not used for native aquatic plant control in FWC funded management programs
|
Non-native |
- Not used for non-native aquatic plant control in FWC funded management programs
|
Invasive
|
- Hydrilla
- Penoxsulam alone ~30 ppb for young stands of actively growing hydrilla in quiescent waters
- Stops hydrilla growth immediately
- Need 60-120 days of exposure for control
- Extended exposure will also control water hyacinth via root uptake
- Penoxsulam ~20 ppb + potassium endothall 1-2 ppb
- Higher rates needed for smaller plots to compensate for dissipation
- Follow with low concentration of penoxsulam for several months for long term control
- Water hyacinth
- Control water hyacinth through root uptake in submersed plant applications at 10-20 ppb, or
- By direct foliar application of 2-4 oz / acre
- Penoxsulam 2-4 oz / ac + flumioxazin 2 oz /ac for water hyacinth / water lettuce mix
- Selective control in bulrush
- Water lettuce control in < 1 wk – hyacinth control ~ 2+ weeks
- Feathered mosquitofern (Azolla pinnata) and Giant salvinia (Salvinia molesta)
- Penoxsulam alone
- Containment or eradication applications
- Applied at 20 ppb in non-flowing waters
|
Plant growth stage (target/non-target) |
- Lower rates may be applicable for young actively growing plants
- Higher rates / longer exposure may be necessary for mature plants or warmer waters
|
Plant susceptibility (target/non-target) |
- Good efficacy for small to large-scale areas of hydrilla in quiescent waters
- Combined with potassium endothall to control hydrilla in higher energy lakes and reservoirs
- Control is faster than with penoxsulam alone
- Hydrilla mats begin to collapse in as little as two weeks
- Seasonal control of non-target native submersed plants such as Illinois pondweed (Potamogeton illinoensis)
- May temporarily impact some emergent plants
- Spikerush (Eleocharis), soft-stem bulrush (Schoenoplectus), pickerelweed (Pontederia) sp.
- Thick lush growth usually recovers next growing season
- Minimize non-target effects by applying when native plants are dormant
|
Potential for regrowth (target/non-target) |
- Effective for annual control of hydrilla, especially when applied with potassium endothall
- Regrowth mostly from sprouting turions/tubers
- Extent of control varies with season and plant growth stage – up to 1-year control
- Older plants with more carbohydrate reserves require a higher dose or longer exposure
- May provide more than 1-year of control of floating plants especially water hyacinth
- For in-water or foliar applications
|
Climate Parameters | Management Considerations |
Weather |
Daily
- Apply when wind/wave action is low to minimize dissipation
Seasonally
- Apply alone for hydrilla control during periods of active growth in quiescent waters
- Combine with potassium endothall for year-round hydrilla applications in Florida waters
|
Light intensity |
- Low intensity
- Reduces submersed plant (hydrilla) ability to recover after application
- May extend penoxsulam half-life (longer half-life in dark waters or during winter months)
|
Water temperature |
- Apply when water temperature generally above 50°F to ensure active growth of target plants
- Enhanced efficacy when applied during active plant growth
|