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Describing Herbicide Selectivity in Aquatics :

The Devil is in the Details

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Managing Plants vs. Expectations

There is a general view that a “right way”

exists to manage invasive aquatic plants

►The problem:

• it is typically done in a state other than your own

Why do aquatic herbicide use patterns

vary so significantly? • State to State (rules/laws)

• Region to Region (problem)

Lakes vs. Reservoirs

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Regional Perspectives on Control

NE and Upper Midwest

Native plant protection is the priority- natural lakes ► Can have 30+ submersed species in a lake

► Thousands of kettle lakes = native plants

Permitting process is often onerous

State Grants – MN and WI – $2+ million

Scale of herbicide use & rates are often dictated

Limited emergent management (WETLANDS!) ► Purple Loosestrife, Phragmites

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Regional Perspective

Southern US

Floating Plant – Kill it

Submersed Plant – Kill it

Emergent Plant – Kill it

Something will re-grow

For perspective – in FL multiple large-scale APM

efforts going on nearly every work day of year

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What is a Herbicide ?

Typically an Organic Compound (ex. ?)

Controlled/Selective Plant Poisoning

►Each herbicide has unique properties

Chemistry of the Herbicide Dictates

►How it behaves in the plant

►How it behaves in the environment

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Me Sequestered in the Vacuole

Mechanisms of Tolerance (Selectivity)

Herbicide X

Not Absorbed

Metabolized to Z

Does Not Bind

To Enzyme Y

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13 Herbicides Labeled for Aquatic Use (223 labeled for terrestrial use)

Copper (1900’s) 2,4-D (1950’s)

Endothall (1960) Diquat (1962)

Glyphosate (1977) Fluridone (1986)

*Dicamba, Dalapon Simazine, Fenac cancelled in 1987)

Triclopyr (2002) Imazapyr (2003)

Carfentrazone (2004) Penoxsulam (2007)

Imazamox (2008) Flumioxazin (2010)

Bispyribac (2011)

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Plant Processes & Herbicides

Photosynthesis – Diquat

Amino Acids and Proteins ► Glyphosate,Imazapyr, penoxsulam, imazamox, penoxsulam,

bispyribac - Slow acting

► Carfentrazon, flumioxazin – fast acting

Cell Membranes – Endothall and Copper

Pigment Synthesis - Fluridone

Growth Regulation – 2,4-D and Triclopyr

Fatty Acid Synthesis, growth inhibition

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Aquatic Herbicides - wide variety of sites,

plants, scale, and application methods

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We treat where people live,

work, & play !

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Vast Majority of Permits

Treatments are small in SCALE

Often Not Designed for Selectivity

►Nuisance Plant Removal

►Diquat + endothall + copper (submersed)

►Glyphosate (emergent)

Selectivity derived from - SMALL SCALE

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Public Waters – Mgmt./Research

Emphasis on Invasive Plants

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The Invasive Elite 8

1. Hydrilla – submersed (spreading nationwide)

2. Sago Pondweed (Native to East U.S.) – Irrigation (W)

3. Eurasian watermilfoil (NE, MW, MS, NW)

4. Water hyacinth- floating (SE, CA)

5. Giant Salvinia – floating (LA, TX, MS)

6. Egeria - submersed (W)

7. Phragmites – (& other grasses)

8. Curlyleaf pondweed - submersed (NE, MW)

Bubble Plants – cabomba, variable milfoil, Trapa,

► Water soldier (Canada)

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The 5th Wave of Hydrilla Invasion Coming to a Northern Tier State Near You ?

Glacial Lakes of the upper MW and NE • 1000’s of lakes with potential to support hydrilla

State policies are mixed • Precautionary principle – we don’t want to know how

bad hydrilla can get (Eradicate)

• We don’t know how bad hydrilla can get (wait & see)

5 to 10 years from now, what will we say? • We saw the early stages of a major new invasion

• Or what was all the fuss about ?

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5 to 10 years from Now

“We saw the early stages of a major new invasion”

“What was all the fuss about - Invasive plants

provide Ecosystem Services”

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50+ years of Diquat Use for Floating Plant Control

“Accept Short-term Non-target plant injury vs. Recovery”

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Both Sides Treated With Different Herbicides

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Submersed Plant Control

Targeting a moving three-dimensional

environment

“Maintaining adequate exposure is crucial”

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BUILDING STRONG® Engineer Research and Development CenterUS Army Corps

of Engineers

TARGET Control Area

Dilution and Dispersion vs. Exposure

Thermal Gradient

Targeting a Moving Three Dimensional Environment

What Influences Selectivity ?

- Scale of Trmt.

- Use Rate of Herbicide

- Timing of Trmt.

No Control Desired

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Submersed Plant Control

Each Herbicide Has a Plant Species Unique Concentration/Exposure Time (CET) Profile

►Concentrations can range from 5 to 5000 ppb

►CET can range from a few hrs to months

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Have we Made the

Selectivity Narrative Too

Simplistic

“Some Herbicides are Selective

and Others are Broad-spectrum”

Good vs. Bad Herbicides

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Glyphosate

Broad-spectrum herbicide that is the most

widely used product in the US

No herbicidal activity in the water – WHY ?

Can control underwater portions of most

emergent plants ► Ex. Flowering rush, Nymphoides, torpedograss

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Glyphosate Translocation ?

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Endothall – -Divergent Activity on Members of the Same Plant Family

-Similar Morphology does not mean similar herbicide activity

Hydrilla Egeria

Lagarosiphon

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Coontail Eurasian Milfoil Variable Milfoil

Parrotfeather Cabomba

Limnophila

Bladderwort

Plant Morphology is Not a Good Predictor of Susceptibility

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Herbicide Tolerance or Resistance

1) Hydrilla – Dioecious or Monoecious biotype

2) Fluridone Tolerant ?

3) Level of Fluridone Tolerance ?

4) Mistake in I.D. = big bucks

1) Eurasian, Northern, or Hybrid Milfoil

2) Fluridone Tolerant (confirmed in MI)

3) 2,4-D Tolerance suspected

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2,4-D – “Classic Selectivity”

Selective for Dicots

►Ex. Key Monocots such as

• Water hyacinth, bulrush, water stargrass

Won’t control several key dicots

►Crested floating heart, cabomba,

Whole-lake treatments- long exposures • Elodea, naiad, vallisneria, thin pondweed

Inherent sensitivity vs. Exposure pattern

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Triclopyr CET Studies: EWM

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Fluridone Concentration

0 25 50 75 100 125 150

Susceptible

Pla

nt S

pecie

s

0

5

10

15

20

25

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Fluridone - Broad spectrum and Selective - Rate Based

EWM, Northern watermilfoil, elodea, Coontail

Chara, Nitella

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Treatment Timing

The same logic used for early treatment of

EWM with fluridone

►Leads to greater sensitivity of Elodea,

Coontail and Northern Milfoil

Elodea and Coontail are much more

tolerant later in the treatment season

►Slower growth rates ?

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Target Plant Biology and Selective Mgmt.

Curlyleaf pondweed – ► Rapid early growth (under ice), senescence in late June/July

► Turions - quiescent and viable for 3+ years

Highly susceptible to endothall ► Most Potamogetons are “highly susceptible to Endothall”

► Treat when CLP is active and Native Plants are “Dormant”

Temporal Selectivity is possible

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Example - Carman’s Bay on Lake Minnetonka - Treated in 2010 and 2011

-96 ac. treated in 2010 – Triclopyr 1.0 mg/L

- 83 ac. treated in 2011 – Triclopyr 1.25 mg/L

2010 results – Milfoil frequency in Sep = 67%

2011 results – Milfoil frequency in Sep = 2%

WHY THE DIFFERENCE ?

1.

2.

3.

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Carmans (outside plot)

Sample Date (June 2011)

8 9 10 11 12 13 14 15

Triclo

pyr,

pp

b

0

50

100

150

200

250

300Site 7

Site 8

Site 9

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Percent frequency results: St. Albans Bay, MN

6/09

6/11

8/09 8/11

Exotic SAV (%)

Eurasian watermilfoil 72 64 70 0

Curly-leaf pondweed 16 6 1 0

Native SAV (%)

Bidens beckii 14 6 8 3.5

Ceratophyllum demersum 41 42 34 50

Elodea Canadensis 14 19 8 18

Najas flexilis 3 4 4 12

Potamogeton amplifolius 16 16 6 21

Potamogeton praelongus 1 0.6 7 5

Potamogeton richardsonii 25 18 11 24

Potamogeton robbinsii 43 44 36 39

Potamogeton zosteriformis 14 22 10 1.7

Ranunculus longirostris 0 6.7 4 0.4

Stukenia pectinata 0 0.6 0 10

Vallisneria Americana 13 0 26 35

Zosterella dubia 0 12 23 1.7

Utricularia spp. 0 0.6 1 2

Myriophyllum sibiricum 2 0 1 1

Chara spp. 11 6 3 11

Littoral samples (depth < 15 ft) 190 190

Samples with SAV 156 173

Native SAV species per point 2.3 2.6

Number of native SAV Species 15 15

St. Albans Bay, MN

Treatment Assessment

1. Exotics at 0% freq.

2. Reduction of 3

native SAV

No change

- SAV per point

- number of SAV

species

- Biovolume and Cover

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St. Albans Bay Top 5

Species

CEDE PORO POAM PORI Chara

dry

we

igh

t (g

)

0

2

4

6

8

10

mean dry weight

St. Albans Bay Low 5

Species

POZO Nitella ELCA ZODU Naiad

dry

we

igh

t (g

)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

mean dry weight

11

11

4 43

71

3 1 1

St. Albans top 7

species

MYSP PORO CEDE POZO ZODU POAM PORI

dry

we

igh

t

0

2

4

6

8

10

mean dry weight

St. Albans low 6

species

RALO ELCA BIBE POPR CHARA POCR

dry

we

igh

t

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

mean dry weight

6

41

1 1 2

17

9

83

5 1 2

6/11 8/11

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Transect June Biovolume2 August Biovolume

20 – 170 29 44

8 – 17 27 46

52 – 198 15 32

233 – 259 27 35

150 – 262 27 28

168 -237 24 45

167 – 236 21 51

22 - 123 22 33

Hydroacoustic Assessment

on Transects in 4 treated

Bays on Minnetonka

No reduction in Plant Volume

between June and August

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1.2 m

Ongoing Research – Focus on EWM and Natives-

Timing, Long-term exposures, Robust plants, etc

Seed Research

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Differing Views on

Selectivity 1) Distribution/abundance of key native

species is most important ► Loss of species vs. injury/recovery

2) Native plants are not impacted during the course of Milfoil control

3) Reduction of some natives-balanced by long-term milfoil control & native recovery

4) Others ?

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Plants Can Sustain Significant Injury but

recover quite rapidly

Efficacy and Selectivity Assessments Can Be

Influenced by When we Make Assessments

Parting Shot

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Why is APM Complex ? Herbicide use patterns have a social dimension

Management philosophies evolve by state and

region (sometimes by county)

Individual biases are a natural part of developing

a statewide management philosophy

► Attitudes towards invasive plants and herbicides

While we want science to drive the process –

► we often don’t view outcomes in the same manner

► Different lakes = different response to the same use

pattern

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Why Is Aquatic Plant Management So Complex ?