Use of Herbicides to Control Aquatic Plants:
Special Challenges Posed by the Submersed Environmentthe Submersed Environment
Michael D. NetherlandResearch BiologistResearch BiologistERDC – Gainesville, FL
US Army Corps of EngineersBUILDING STRONG®
What Challenges ?What Challenges ?
Regulatory requirementsRegulatory requirements►Aquatic Label, State Permits, Federal Permits
Stakeholder Pressure Stakeholder Pressure►Public waters = heavy public scrutiny
T h t l t h t l ti i• Too much control, not enough control, timing….►Private waters = high expectations
f S Technical Aspects of Submersed Use Patterns
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We treat where people live,k & l !work, & play !
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12 Herbicides Labeled for Aquatic Use(223 labeled for terrestrial use)(223 labeled for terrestrial use)
Copper (1900’s) 2,4-D (1950, 76)pp ( ) , ( , )
Endothall (1960) Diquat (1962)
Glyphosate (1977) Fluridone (1986)Glyphosate (1977) Fluridone (1986)*Amitrole, Dicamba, Dalapon Simazine, Fenac,
Dichlobenil, Silvex (most cancelled in 1987)
Triclopyr (2002) Imazapyr (2003)
C f t P lCarfentrazone (2004) Penoxsulam (2007)
Imazamox (2008) Flumioxazin (2010)
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A Further look at Aquatic HerbicidesA Further look at Aquatic Herbicides
8 Modes of action (16 defined MOA)
7 Enzyme specific inhibitors (3 ALS inhibitors)
Glyphosate Imazapyr – emergent use onlyGlyphosate, Imazapyr emergent use only No Aquatic Label
• ACCase inhibitors PS II inhibitors Mitosis inhibitors• ACCase inhibitors, PS II inhibitors, Mitosis inhibitors, Lipid biosynthesis inhibitors
Are any herbicides used for aquatics only?Are any herbicides used for aquatics only?• Fluridone, Endothall• All have a terrestrial history
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Aquatic Herbicides – a wide variety of sites, plants, application methods,sites, plants, application methods,
formulations
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Treatment Principles - the SameTreatment Principles the Same
Proper Plant I DProper Plant I.D. Know the Strengths and Weaknesses of
the Herbicidesthe Herbicides How might Environmental Conditions
I t th T t t ?Impact the Treatment ? Concentration and Exposure Relationships
• Submersed
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Plant IdentificationPlant Identification
Numerous submersed plants Numerous submersed plants ►Beneficial and Invasive
S i i dl Some sites require mgmt. regardless of species►Use of water body
Proper Identification = Proper MgmtProper Identification Proper Mgmt.
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Hydrilla
Monoecious or Dioecious?Egeria densa E. najas
??
High Phenotypic Plasticity
Elodea ?
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Variable MilfoilEurasian Hybrid Northerny
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Cabomba
Algae as Invasive Plants ?AVM – linked to birddeaths
Microcystis bloom in FL
Golden AlgaeMassive FishKills in TX
Golden Algae
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Prymnesiumparvum
Submersed Plant ControlSubmersed Plant ControlTargeting a moving three-dimensionalTargeting a moving three-dimensional
environment“M i t i i d t i i l”Maintaining adequate exposure is crucial”
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Product Dispersion – An issue of S lScale
Race Between Vertical MixingAnd Lateral Dispersion
Diquat hrs of exposure
P d t Di i
Diquat – hrs of exposureEndothall – 1-7 days of exposureFluridone – 60+ days of exposure
TARGET Control Area
Product Dispersion
Thermal Gradient
BUILDING STRONG®Engineer Research and Development CenterUS Army Corpsof Engineers
Use of Herbicides for S b d Pl tSubmersed Plants
You Treat the Water to Achieve aYou Treat the Water to Achieve a Desired Aqueous Concentration►You are Targeting the Plants !►You are Targeting the Plants !
Each Herbicide Has a Plant Species Unique Concentration/ Exposure ProfileConcentration/ Exposure Profile►Concentrations can range from 5 to 5000 ppb►Exposure requirements can range from a►Exposure requirements can range from a
few hours to months
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Misconceptions with Aquatic HerbicidesHerbicides
Aquatic plants “take up” most of the herbicideq p p• Plant uptake = 1 to 5 % of herbicide
Herbicides mix rapidly top to bottomy• Herbicide trapped via thermal gradients
Dispersion is a minor factor• e.g. All 3 ppm treatments should work the same• Wind/Flow move herbicide off-target
Herbicides Are Just Dumped Into the Water
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Conditions can changePlant Density & Growth Rate Conditions on the DOT
Many Factors Impact Submersed Applications
Conditions can changePlant Density & Growth Rate Conditions on the DOT
Water quality / temp / epiphytes Water exchange (CET) Trmt. Block & edge/ acre
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Linear Flow Systems (1)Linear Flow Systems (1)
If you know the water flow rate (CFS), you can Inject a desired concentration for a known time !!j
- single injection site = 100’s of miles of control
E d h ll-Endothall - registered in 1960 completed food tolerance studies in 2009 and significantly changed an entire market
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Linear Flow Systems (2)Linear Flow Systems (2)
Short distance canals – significant challengee.g. 1 mile canal flowing at 10 CFS
Flow estimates can be crude (dye)
Easy Hard HygrophilaHydrilla
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What Makes Hygrophila so Challenging ?
Emergent form is susceptible to several herbicides - Excellent control on dry groundy g
Long concentration and exposure requirements = high cost and high volume-high cost and high volume
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Submersed Treatment Strategies for Floating and Floating Leaf Plants ?
Giant Salvinia D i th CGiant Salvinia Deep in the Cypress
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Hydrilla – Moving NorthEurasian Watermilfoil –
- Northern Lakes- Hybridization
Curlyleaf Pondweed –Northern Lakes
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Endangered species AVM and waterfowl mortality
Native Plant Impacts, Monitoring Flood Control /Structures
Multi-agency jurisdiction - Access/Navigation/Recreation
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Why Manage Milfoil or Hydrilla ?Why Manage Milfoil or Hydrilla ? Provides Structure and Food
► Hydrilla same role as native plants► Hydrilla- same role as native plants► Clears up the water
Do Not Produce Toxins (e.g. golden algae)( g g g )
Valued by the Fishing and Hunting Communities► “ Fishing the Edge” “Ringneck duck buffet”
Growth Rate and Ability to Occupy Vast Contiguous Areas are the ProblemContiguous Areas are the Problem► Access, Flood Control, Fishery Mgmt.► Water Quality
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y► “Just leave us a little”
Is there a right amount of an invasive plant ?s t e e a g t a ou t o a as e p a t(Do we want 30% coverage for fisheries?)
If so, then how do you maintain that level ?
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Vallisneria or Eel Grass
Illinois Pondweed
Management of Submersed Aquatic Vegetation
Vallisneria or Eel Grass
Southern Naiad
Strap Leaf Sagittaria
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Maximizing SelectivityMaximizing Selectivity
Timing can have a major impact onTiming can have a major impact on selectivity►Different species have maximum growth at►Different species have maximum growth at
different times Species composition is very important in Species composition is very important in
herbicide selection- lack of impacts to non-targets may be equally or morelack of impacts to non targets may be equally or more
important than impacts on the target.
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Slow Acting Enzyme-Specific Inhibitors
Fl id (1986) PDS i hibit P l Fluridone (1986) PDS inhibitor, Penoxsulam (2007) ALS inhibitor
L li d fi h t i it►Low mammalian and fish toxicity • No restrictions on drinking, swimming, fishing
►Use rates in the range of 5 to 20 ppb►Use rates in the range of 5 to 20 ppb►Long-term exposures required►Whole-lake or large scale use►Whole lake or large scale use ►Large body of research on whole-lake fluridone
for control of EWM
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for control of EWM
Auxin-Mimic HerbicidesAuxin Mimic Herbicides 2,4-D (1959, 1976) and Triclopyr (2002)-
disrupt growth & metabolismdisrupt growth & metabolism►Epinasty (bending of leaves and stems)
T l t d i hl►Translocated in phloem ►Many monocots are highly tolerant►Used for both submersed and emerged plants
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Contact Herbicides(Diquat, Endothall, Flumioxazin)- What does that mean in Aquatics?- What does that mean in Aquatics?
• Do not Kill on Contact (e.g. bleach)M t i “C t t” ith th l t• Must come in “Contact” with the plant tissue for an appropriate / critical period of timetime
• Application techniques are very important • Not readily translocated in the plant tissue• Not readily translocated in the plant tissue
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Environmental FatePhotolysis – fluridone & penoxsulam (7-30 d),
triclopyr and imazamox (4-10 d)Microbial – 2,4-D (4-10 d), endothall (2-10 d)Hydrolysis – carfentrazone, flumioxazin (hrs to 1 y y , (
day – pH)Deactivation –
diquat – negatively charged particles (sediments – minutes to days – WQ)Glyphosate – binds to cation ions (Ca,Mg) –minutes
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Once Initiated - Herbicide Approach RequiresApproach Requires
Vigilance- Rare for one treatment to “solve” a problem
- Early detection /rapid Response Programs- Eradication programs – multiple years- Invasive Plant Mgmt – multiple years- Invasive Plant Mgmt. multiple years- Rare for one treatment to “ruin” a lake
W h bi id t ibl- Wrong herbicide or use rate – possibly- Right herbicide and use rate - No
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Advantages of Herbicide UseAdvantages of Herbicide Use Can treat small as well as large areas
►Target site is reasonably defined Proper choice & rate = selectivity Newer Products – strong toxicology profiles Compatible with other toolsCompatible with other tools Best tool for initially removing large
amounts of invasive vegetationamounts of invasive vegetation
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Disadvantages of Herbicide sad a tages o e b c deUse
Commitment to long-term management CostCost Can sometimes select for a worse problem
T t Pl t ill lti t l Target Plants will ultimately recover Public perception of chemical use
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Questions to Ask What is the Major Use of the Water ?
►Irrigation, retention, recreation, multipurpose Where Does the Treated Water Go ?
►What is downstream & how fast does it get there Are Fish an Important Resource ?p
►Pay attention to water temp., DO, plant mass Is site susceptible to rapid turnover ?Is site susceptible to rapid turnover ?
►Flow, significant rain event
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