Use of Herbicides for Control ofSubmersed Vegetation

Jeremy G. SladeUnited Phosphorus, Inc.

Gainesville, FL

Flood Control and Water Delivery

Protect Wildlife Habitat

Water Use: Hunting? Fishing? Skiing?

Invasive Species Disrupt Ecosystems

The Scale and Type of Management Can Vary Significantly

Aerial – Large Lake Irrigation Mgmt.

Airboat – Small area FL Spring – Injection Trmt

The Principles Remain the Same

• Proper Plant Identification• Know the Strengths and Weaknesses of the

Herbicides• Concentration and Exposure Relationships• How might Environmental Conditions

Impact the Treatment

Plant Identification

• Numerous submersed plants – Native and Invasive

• Some sites require management regardless of species– Use of water body

• Proper Identification = Proper Mgmt.

Elodea ?

HydrillaMonoecious or Dioecious?

Egeria densa E. najas

Variable Milfoil

Herbicide Response ?

Cabomba

Eurasian Hybrid Northern

Vallisneria or Eel GrassIllinois Pondweed

Southern Naiad

Management of Submersed Aquatic Vegetation

Strap Leaf Sagittaria

Algae as Invasive Plants ?AVM – linked to birddeaths

Microcystis bloom in FL

Massive FishKills in TX

Golden Algae

Prymnesiumparvum

Management AlternativesVery Limited ! Research

Sago Pondweed – Western Irrigation-Widespread use of Acrolein and Xylene (toxicants)

-Acrolein fish kill in OR

-Some Mechanical Control – “Chaining”

-Irrigation Districts – small “empires” resistant to change-Endothall recently receives registration; pre-emergent evaluations

NPDES permits in West,and now US

Why Manage Hydrilla or Milfoil?• Provides Structure and Food

– Hydrilla - same role as native plants– “Clears up the water”

• Do Not Produce Toxins (e.g. golden algae)

• Valued by the Fishing and Hunting Communities– “ Fishing the Edge” “Ringneck duck buffet”

• Growth Rate and Ability to Occupy Vast Contiguous Areas are the Problem– Access, Flood Control, Fishery Mgmt.– Water Quality– “Just leave us a little”

Hydrilla has several key competitive advantagesRapid Canopy formation (no native canopy formers)Low light and CO2 compensation pointsAbility to withstand low oxygen (C4-like photosynthesis)Ability to withstand high temps (canopy > 40 C)

Progression of Hydrilla SpreadYear Number

of States States

1960 – 1969 1 FL (1959)

1970 –1979 6 AL, CA, DE, GA, LA

1980 – 1989 13 CT, MD, MS, NC, SC, TX, VA

1990 – 1999 17 AR, PA, TN, WA

2000 – 2011 29 ID, IN, KY, MA, ME, NJ, NY, OK, WI, WV, KS, OH

AZ – hydrilla extirpated 1985

Hydrilla – Moving North Eurasian Watermilfoil –- Northern Lakes- Hybridization

Curlyleaf Pondweed –Northern Lakes

Is there a right amount of an invasive plant ?

If so, then how do you maintain that level ?

Once Initiated - Herbicide Approach Requires Vigilance

- Rare for one treatment to “solve” a problem- Early detection/Rapid Response Programs

- Eradication programs – multiple years- Invasive Plant Mgmt. – multiple years- Rare for one treatment to “ruin” a lake

- Wrong herbicide or use rate – possibly- Right herbicide and use rate - No

13 Herbicides Registered for Aquatic Use

• All products have terrestrial uses (fluridone)– Glyphosate and 2,4-D- major use on food crops

• Glyphosate and Imazapyr- Emergent• Copper, Endothall, Fluridone- Submersed• Diquat, 2,4-D, Clipper, Triclopyr,

Carfentrazone, Imazamox, and Penoxsulam, Bispyribac-sodium– Both emergent and submersed uses

Herbicides for Submersed PlantsProduct Use Rates NotesCopper 0.25 to 1 Algae, no use restrictions

(1900’s) Irrigate Immediately2,4-D 1.0 to 4.0 Selective Milfoil Control

(1950, 76)Diquat 0.15 to 0.37 Short exposure requirement

(1958) Turbidity impacts efficacyEndothall 1.0 to 3.0 Key contact for Hydrilla

(1960) Fishing restriction removed 06Fluridone 0.01 to 0.09 Large-scale mgmt; hydrilla,

(1986) control can take 1 to 3 monthsTriclopyr 0.5 to 2.5 Selective Milfoil Control

(2002)

Herbicides for Submersed PlantsProduct Use Rates NotesCarfentrazone 0.1 to 0.4 Variable Milfoil, Cabomba

(2004)Penoxsulam .01 to .03 Combo w/endothall for Hydrilla

(2007)Imazamox .05 to 0.2 Growth Regulation of Hydrilla

(2008)Flumioxazin 0.1 to 0.4 Cabomba, Variable Milfoil

(2010)Bispyribac-sodium .02 to .045 Combo w/endothall for Hydrilla

(2011)Topramezone 2013??

Conditions can changePlant Density & Growth Rate Conditions on the DOT

Many Factors Impact Submersed Applications

Water quality / temp / epiphytes Water exchange (CET) Trmt. Block & edge/ acre

Use of Herbicides for Submersed Plants

• You Treat the Water to Achieve a Desired Aqueous Concentration– You are Targeting the Plants !

• Each Herbicide Has a Plant Species Unique Concentration/ Exposure Profile– Concentrations can range from 5 to 5000 ppb– Exposure requirements can range from a

few hours to months

Rate of Dilution/Dispersion Effects Efficacy Following Application

Calm Day(Good Lines)

Windy Day(Rapid Mixing)

Plant Density Can be Very Different – But Does Not ChangeRecommended Use Rate

Plant Density – Can effect distribution, thermal gradientsGranular vs. Liquid; Trailing Hoses; Time of Day

(15 F Temp diff. top/bottom)

Engineer Research and Development CenterUS Army Corpsof Engineers

TARGET Control AreaTARGET Control Area

Dilution and Dispersion vs. ExposureDilution and Dispersion vs. Exposure

Thermal Gradient

Product Dispersion

Race Between Vertical MixingAnd Lateral Dispersion

Misconceptions with Aquatic Herbicides

• Aquatic plants “take up” most of the herbicide• Plant uptake = 1 to 5 % of herbicide

• Herbicides mix rapidly top to bottom• 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 “Dumped” Into the Water

Rates are calculated on a volume basis – pumps calibrated to deliver a dose based on boat speed (GPS)

3 ppm in 10 acres with 6 foot avg. depth = 115 gallons Aquathol into 19.6 million gallons of water

Can Use GPS to insure that applicator is applying evenly vs “dumping”

Slow Acting Enzyme-Specific Inhibitors

• Fluridone (1986) PDS inhibitor, Penoxsulam (2007) ALS inhibitor –– Low mammalian and fish toxicity

• No restrictions on drinking, swimming, fishing– Use rates in the range of 5 to 20 ppb– Long-term exposures required– Whole-lake or large scale use – Large body of research on whole-lake fluridone

for control of EWM

Auxin-Mimic Herbicides• 2,4-D (1959, 1976) and Triclopyr (2002)-disrupt

growth & metabolism of sensitive species– Epinasty (bending of leaves and stems)– Translocated in phloem (moves through the plant)– Many monocots are highly tolerant– Used for both submersed and emerged plants

Contact Herbicides (Diquat and Endothall)

- What does that mean in Aquatics?• Do not Kill on Contact (e.g. bleach)• Must come in “Contact” with the plant tissue

for an appropriate / critical period of time• Application techniques are important for these

compounds (submersed)• Not readily translocated in the plant tissue

Environmental FatePhotolysis – fluridone (7-30 d), triclopyr (2-7 d)

penoxsulam (7-30 d), imazapyr (4-10 d)Microbial – 2,4-D (4-10 d), endothall (2-7 d),

bispyribac-sodium (30-45 d)Hydrolysis – flumioxazin and carfentrazone (hrs to 1

day – pH)Deactivation – diquat – negatively charged particles

(sediments – minutes to days – WQ)Glyphosate – binds to cation ions (Ca,Mg) – minutesCopper – forms complexes that are not

biologically active

Maximizing Selectivity• Timing can have a major impact on

selectivity– Different species have maximum growth at

different times– E.g. Curlyleaf pondweed

• Species composition is very important in herbicide selection- lack of impacts to non-targets may be equally or more important than

impacts on the target

Advantages of Herbicide Use

• Can treat small as well as large areas– Target site is reasonably defined

• Proper choice & rate = selectivity• Newer Products – excellent toxicology profiles• Compatible with other management options• Best tool for initially removing large amounts

of invasive vegetation

Disadvantages of Herbicide Use

• Commitment to long-term management• Cost ($ to $$$)• Can sometimes select for a worse problem

– Hydrilla Hygrophilia or Limnophila• Target plants will ultimately recover• Public perception of chemical use

– Typically based on how it “use to be”

The Situation Matters: Not all infestations are viewed as having equal impact

Stakeholders often determine the level of management

At some large reservoirs managers accept that an invasive is going to remain dominant

Targeted Management – Priority Zones

Lake Seminole and Lake Eufaula – COE Reservoirs

Questions to Ask• What is the Major Use of the Water ?

– Irrigation, retention, recreation, multi-purpose• Where Does the Treated Water Go ?

– What is downstream and how fast does it get there• Are Fish an Important Resource ?

– Pay attention to water temperature, DO, plant mass• Is the site susceptible to rapid turnover ?

– Flow, significant rain event

Be Careful Out There!!