Use of Herbicides for Control ofSubmersed Vegetation

Michael D. Netherland, Ph.D

US Army ERDC, Gainesville, FL

The Scale and Type of Herbicide Use Can Vary Significantly

Aerial – Large Lake Irrigation Mgmt.

Airboat – trailing hose

FL Spring – Injection Trmt

Treatment Principles Remain the Same

• Proper Plant I.D.• Know the Strengths and Weaknesses of the

Herbicides• Concentration and Exposure Relationships• How might Environmental Conditions

Impact the Treatment ?

Plant Identification

• Numerous submersed plants – Beneficial and Invasive

• Some sites require mgmt. regardless of species– Use of water body

• Proper Identification = Proper Mgmt.

Elodea ?

HydrillaMonoecious or Dioecious?

?

Egeria densa E. najas

High Phenotypic Plasticity

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

Why Manage Milfoil or Hydrilla ?• 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 – Moving North Eurasian Watermilfoil –- Northern Lakes- Hybridization

Curlyleaf Pondweed –Northern Lakes

Is there a right amount of an invasive plant ?(Do we want 30% coverage for fisheries?)

If so, then how do you maintain that level ?

Does Hydrilla Actually Grow an Inch a Day ?

• Data often presented in terms of biomass– E.g. 400 grams dry wt. /square meter– E.g. 1936 Kg dry wt. / square meter

• We designed a study to measure elongation– How many inches does hydrilla grow per day ?– Study conducted at US Army ERDC LAERF

Single 4 inch stem planted and given a 1 week growth period.Plants were harvested at weekly intervals & measured for total length

Study 2 – Planted Established hydrilla (~ 1 ft tall) in 10 ft tanksHow long until plants reach the surface ?

1.2 M

3.5 M

Harvest Date

7/23/09 7/30/09 8/6/09 8/13/09 8/20/09 8/27/09

Tota

l Len

gth

of N

ew G

row

th (i

n)

0

500

1000

1500

2000

2500

3000

3500

2.9 11.5

58.8

182.3

191.735 ± 209 ± 63 ± 21 ± 10 ± 0Runners

130 ± 6371 ± 1634 ± 136 ± 12 ± 0New Stems

137 ± 38109 ± 2943 ± 1113 ± 62 ± 2Laterals

Week 5Week 4Week 3Week 2Week 1

- A single 9 inch shoot resulted inover 3200 inches of growth in 5 weeks

-Established 1 foot tall plants took8 days to reach the surface in 10 ftwater depth

- Elongation = 1+ foot /day

Hydrilla change ininches over 35 d

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

11 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, Triclopyr, Carfentrazone,

Imazamox, and Penoxsulam – Both emergent and submersed uses

Herbicides for Submersed PlantsUse Rates (ppm) Notes_________

Copper 0.25 to 1 Algae, no use restrictions(1900’s) Irrigate Immediately

2,4-D 1.0 to 4.0 Selective Milfoil Control(1950, 76)

Diquat 0.15 to 0.37 Short exposure requirement (1958) turbidity impacts efficacy

Endothall 1.0 to 3.0 Key contact for Hydrilla(1960) Fishing restriction removed 06

Fluridone 0.01 to 0.09 Large-scale mgmt; hydrilla,(1986) control can take 1 to 3 months

Herbicides for Submersed PlantsUse Rates (ppm) Notes_________

Triclopyr 0.5 to 2.5 Selective Milfoil Control(2002)

Carfentrazone 0.1 to 0.4 Variable Milfoil, Cabomba(2004)

Penoxsulam .01 to .09 Large-scale hydrilla mgmt. (2007)

Imazamox .05 to 0.2 Growth Regulation of Hydrilla(2008)

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 Rate of Dilution/Dispersion Effects Efficacy Following ApplicationEfficacy Following Application

Good Lines (Calm)

Windy Day- rapidmixing)

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 difference top/bot)

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

Slow Acting Enzyme-Specific Inhibitors

• Fluridone (1986) PDS inhibitor, Penoxsulam (2007) and Imazamox (2008) 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

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

-Acrolein fish kill in OR -Some Mechanical Control - Chains

-Irrigation Districts – small empires resistant to change

-Endothall (1958) recently received registration for new use pattern

NPDES permits in West

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)Hydrolysis – 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• Can sometimes select for a worse problem• Target Plants will ultimately recover• Public perception of chemical use

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 – COE Reservoir

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

– Irrigation, retention, recreation, multipurpose• 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

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