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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