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BUILDING STRONG®
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
8
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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 ?
14
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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”
20
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
23
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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
31
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 ?
32
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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 ?
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