Environmental Fate of Aquatic HerbicidesHerbicides

UF IFAS Aquatic Weed Control ShortUF-IFAS Aquatic Weed Control Short Course

Michael Netherland Ph DMichael Netherland, Ph.DUS Army Engineer Research & Development Center

US Army Corps of EngineersBUILDING STRONG®

What Happens After You Spray ?What Happens After You Spray ?

Emergent vs Submersed Applications Emergent vs. Submersed Applications• Emergent plants intercept a large % of the product• Submersed trmt. – uptake is a minor factor (1 to 4 %)Submersed trmt. uptake is a minor factor (1 to 4 %)

Different volumes for emergent & submersed control • 2,4-D = ~ 2 qts/acre emergent, q g• 2,4-D = ~20 qts/acre submersed

Herbicides ultimately reach the water columny• How long do they persist and how do they degrade ?

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Submersed biomass does not correlate with a significant removal (uptake) of herbicidea significant removal (uptake) of herbicide

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Emergent TreatmentsBulk of product is initially absorbed by emergent plant tissue

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Amount that enters the water depends on the density of the plant standon the density of the plant stand

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Is Herbicide Released from Treated Vegetation ?

-Can be metabolized by tolerant plants-Non-herbicidal compounds

Can be sequestered in vacuoles-Can be sequestered in vacuoles-Can be bound to organic constituents-Can be slowly released from decaying plant matterCan be slowly released from decaying plant matter

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Herbicide DispersionHerbicide Dispersion

Aquatic herbicides disperse in waterAquatic herbicides disperse in water ► movement from the treatment site

• Flow winds scale of treatment - drive dispersion• Flow, winds, scale of treatment - drive dispersion

Concentrations can be rapidly dilutedDil ti i t th d d ti Dilution is not the same as degradation►Dilution can result in concentrations being too

l f h bi id l ti itlow for herbicidal activity

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Rate of Dispersion – Major influence on Efficacyon Efficacy

e.g. Fluridone vs. Diquat

P d t Di i

g q

TARGET Control Area

Product Dispersion

Thermal Gradient

BUILDING STRONG®Engineer Research and Development CenterUS Army Corpsof Engineers

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Lakes Woodruff and Dexter – Natl. Wildlife Refuge – 12/07

- Woodruff ~ 750 / 2200 acres treated at 2.0 ppmDexter ~518/ 1800 acres treated at 3 0 ppm- Dexter ~518/ 1800 acres treated at 3.0 ppm

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12 Herbicides Registered for Aquatic Use

Copper (1900’s) 2 4-D (1950’s)Copper (1900 s) 2,4 D (1950 s) Endothall (1960) Diquat (1962)

Gl h t (1977) Fl id (1986) Glyphosate (1977) Fluridone (1986) Triclopyr (2002) Imazapyr (2003) Carfentrazone (2004) Penoxsulam (2007) Imazamox (2008) Flumioxazin (2011)Imazamox (2008) Flumioxazin (2011)

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Primary Mode of DegradationPrimary Mode of Degradation

Photolysis (5/12)Photolysis (5/12) Inactivation followed by microbial (2/12)

Mi bi l D d ti (2/12) Microbial Degradation (2/12) Hydrolysis (2/12) Copper (1/12) – elemental

►Biologically inactive but never broken down►Biologically inactive but never broken down

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Photolysis (5 of 12 Products)Photolysis (5 of 12 Products)

Energy from sun breaks chemical bondsgy• Ultraviolet (uv) light• Different wavelengths of uv for different molecules

Fluridone and Penoxsulam –• half-lives 20 to 50 days

Triclopyr, Imazapyr, and Imazamox • half-lives average 5 to 14 daysg y

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PhotolysisPhotolysis Photolysis occurs in the top few inches of lakePhotolysis occurs in the top few inches of lake

water How does water depth impact the rate of p p

degradation ? Can photolysis occur below a thermocline ?p y Can photolysis occur below a dense plant mat ? Molecules split by photolysis into smaller partso ecu es sp t by p oto ys s to s a e pa ts

► Photolysis, microbial, hydrolysis,

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Photolytic Degradation of Fluridone

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Photolysis and EfficacyPhotolysis and Efficacy

Fluridone and PenoxsulamFluridone and Penoxsulam ►Product longevity = improved efficacy

Imazapyr, Imazamox, Triclopyr – emergent►Herbicide in plant tissue not subject to

photolysis

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Inactivation (3/12)Inactivation (3/12) Diquat, Glyphosate and Copper-

inactivated in water►Half-lives can be hours to days (water quality)►Impacts efficacy on submersed plants

Molecules exist as ions in water►Diquat ++ Glyphosate – Copper++

Ionic bonds = inactivation Ionic bonds = inactivation ►No further herbicidal activity (water or soil)

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Clay and Organic Matter = High surface area and full of negative charges

Diquat = ++ charges

Once diquat is bound to sediment – microbial degradation proceeds very slowly- half-life > 1000 days

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Copper (micronutrient)Copper (micronutrient)

Copper is inactivated but does not degradeCopper is inactivated but does not degrade►Rapidly removed from water column

Forms numerous complexes and ultimately Forms numerous complexes and ultimately resides in sediment

Bi l i ll ti ?►Biologically active ? Florida – heavy use for private sector

(algae), limited use in public waters

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Microbial Degradation (2/12)Microbial Degradation (2/12) Endothall and 2,4-D microbial degradation , g

is the primary pathway ►Source of carbon (energy/food) for microbes►Some microbes specialize on herbicides

All aquatic herbicides are subject to microbial degradation (one key exception)►What factors dictate the rate of degradation ?

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Factors that Influence Microbial Degradation

TemperatureTemperature►We use cold temperature to extend exposure

Prior application Prior application►Efficient microbe populations can be selected

Water (aerobic) vs. Sediment (anaerobic)►Oxygen can enhance or inhibit breakdown

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Effect of Temperature on Microbial Degradation of Endothall

2000

16 C21 C27 C

1500ppb

1000

End

otha

ll,

500

E

0 24 48 72 96 120 144 168

0

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Hours Posttreatment

Enhanced DegradationEnhanced Degradation Enhanced microbial degradation is well-Enhanced microbial degradation is well

described in terrestrial settings Soil half-life of 2,4-D can decrease withSoil half life of 2,4 D can decrease with

increasing use pattern As long as enhanced degradation does notAs long as enhanced degradation does not

impact efficacy, it is viewed as positive

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Lake Tomahawk, WI – 2008• 250 acres of 2 4-D at 0 5 ppm• 250 acres of 2,4-D at 0.5 ppm• 1st Time Lake had been treated

½ Life in Water = > 50 days500

600

3 days of exposure will kill milfoil at this rate2,

4 D

, ppb

200

300

400

Severe reductions or loss of 21 species including “tolerant”Sample Date

May 14May 28 Jun 10 Jul 8 Jul 260

100

species including tolerant monocots

Sample Date

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Enhanced Fluridone DegradationEnhanced Fluridone Degradation

In several FL lakes with significant use In several FL lakes with significant use history, we observed: 1) Rapid degradation of fluridone 1) Rapid degradation of fluridone

►Degradation in the dark►Half-lives of fluridone < 3 days►Half-lives of fluridone < 3 days►Narrowed to enhanced microbial activity

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Hydrolysis (2/12)Hydrolysis (2/12)

Both Flumioxazin and Carfentrazone areBoth Flumioxazin and Carfentrazone are degraded by hydrolysis Process can result in rapid degradation Process can result in rapid degradation pH-dependent (flumioxazin)

►pH 5 - 4 days►pH 7 - 24 hours►pH 9 – 22 minutes

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Miscellaneous QuestionsMiscellaneous Questions

Are aquatic herbicides subject toAre aquatic herbicides subject to volatilization? What is adsorption and desorption ? What is adsorption and desorption ?

►Think fluridone and organic matter f f How does degradation of herbicides from

granular formulations compare to liquids ? Is this guy ever going to stop talking ?

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SUMMARY– Herbicides subject to degradationj gPrimary & Secondary Modes of Degradation

2,4-D (2, 1) Diquat (3 2) Diquat (3, 2) Endothall (2) Flumioxazin (4 2)

1) Photolysis2) Microbial Degradation3) Inactivation Flumioxazin (4,2)

Fluridone (1,2)Glyphosate (3 2)

3) Inactivation4) Hydrolysis

Glyphosate (3, 2) Imazamox (1, 2)

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