the biology and management of hydrilla
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BUILDING STRONG®
The Biology and Management of Hydrilla
Michael D. Netherland
US Army Engineer Research and Development Center
Gainesville, FL
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Does Hydrilla Pose a Greater
Threat to Missouri Waters
Than Other Invasive Plants ?
Hydrilla Eurasian Milfoil Curlyleaf Pondweed
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Overview Hydrilla
►Life history
►The “Perfect Weed”
► Invasion History
Factors Impacting Establishment & Spread ► Abiotic contraints
Control Methods
Feasibility of Eradication
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Hydrilla verticillata L.f. Royle
Hydrilla is a monocot - Hydrocharitaceae family
► Elodea, Egeria, and Vallisneria
► Early detection ?
Native to tropical SE Asia
► Found on 6 Continents as far North as Poland
Dioecious and Monoecious Biotypes
► Separate Introductions to the US
► Worldwide – Monoecious is tropical and Dioecious is
temperate
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Hydrilla - “The Almost Perfect Weed”
* Ability to cover thousands of contiguous acres
* propagates by fragments, turions, tubers, crowns
- tubers can remain quiescent for years (seed)
* Low light and CO2 compensation points
* Clonal plant - but high genetic diversity
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Why Plant Biology Matters ?
What is it about Hydrilla that
Allows it to Grow to Such
Abundance ?
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Does Hydrilla Grow an Inch per
Day ?
Data often presented in terms of biomass
►E.g. 400 grams dry wt. /square meter
Single 4” shoot grown for 35 days
1.2 M
BUILDING STRONG® Harvest Date
7/23/09 7/30/09 8/6/09 8/13/09 8/20/09 8/27/09
To
tal L
en
gth
of
New
Gro
wth
(in
)
0
500
1000
1500
2000
2500
3000
3500
2.9 11.5
58.8
182.3
191.7
Week 1 Week 2 Week 3 Week 4 Week 5
Laterals 2 ± 2 13 ± 6 43 ± 11 109 ± 29 127 ± 38
New Stems 2 ± 0 6 ± 1 34 ± 13 71 ± 16 110 ± 63
Runners 0 ± 0 1 ± 1 3 ± 2 9 ± 6 35 ± 20
-A single 9 inch shoot resulted
in over 3200 inches of growth in
5 weeks
Hydrilla change in
inches over 35 d
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Hydrilla
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Dioecious Hydrilla
Southern Distribution in the US
► Clonal female population
Tubers produced - day length < 12 hr
► Fall production (short window in North)
► May switch to axillary turions in North (rapid process)
Rapid Canopy formation
► Internodes measured in feet
Fluridone Resistant Populations are in FL
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Monoecious Hydrilla
Northern Distribution in the US
Tubers produced in summer
Dies Back in Winter (propagules)
Rapid lateral expansion
►Competitive interactions not documented
Multiple Eradication Programs Ongoing
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Greatest Threat to Missouri ?
Monoecious Biotype May be Well Suited to
Missouri
►Tolerates much higher disturbance
►Reservoir fluctuations
►Found in Reservoirs throughout the S.E.
►Becoming well established in TVA reservoirs
• Expansion westward
►We know much less about monoecious hydrilla
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Significant Milfoil or Hydrilla Presence
High Energy Reservoirs /
Turbid with water level fluctuations
Generally not conducive to SAV (Monoecious hydrilla ? )
Natural Lakes
Reservoirs
Ohio River – Hydrilla
Expanding where no SAV
Was previously noted
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Progression of Hydrilla
Spread Year Number
of States States
1960 – 1969 1 FL (1953)
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 – 2010 29 ID, IN, KY, MA, ME, NJ,
OK, WI, WV, NY, KS, OH
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Water Bodies in Wake County, NC with Hydrilla
Year Surveyed
Nu
mb
er
of
Wa
ter
Bo
die
s
0
10
20
30
40
50
60
70
1980 1982 1984 1986 1989
1 2
1012
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Small Landscape Pond in NC
Each Water Body Requires an INTRODUCTION !
Lake Gaston, NC
Plants move from large to small
water bodies and vice versa
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Hydrilla in Wisconsin Pond –
Response by DNR
Completely drained pond for
winter drawdown
Spring 08- refilled and
treated with fluridone
Positive i.d. in fall of 07
Why such a strong response ?
Where did the hydrilla come from ?
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Management Options Are
Limited
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Environmental Extremes
Grass Carp – SE Reservoirs Selective Biocontrol
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Hydrilla Management
Grass Carp –
►“All or None control” in large systems
►generally non-selective or at least non-
predictable
►Still no efficient means for removal of fish
►Limited use in northern lakes due to low
preference for milfoil
• Cold water can reduce feeding
efficiency/predictability
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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)
*Amitrole, Dicamba, Dalapon Simazine, Fenac,
Dichlobenil, Silvex (most cancelled in 1987)
Triclopyr (2002)
Imazapyr (2003) Carfentrazone (2004)
Penoxsulam (2007) Imazamox (2008)
Flumioxazin (2010) Bispyribac (2011)
Blue = Plant Enzyme Specific Inhibitors
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Thousands of Harvesters - Winter Biomass Control , FL
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California – Eradication Policy
Ongoing Eradication efforts for 30+years
► concern = agricultural irrigation
Aggressive and Immediate Action
Clear Lake (~ 40,000 acres)
►Eradication policy
►Treat 5 acres around individual plant finds
►Poor Economics on an acre basis / Good overall Policy ?
Nationwide Eradication projects > 6 years
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Hydrilla and Ecosystem Services
Provides Structure and Food ► Hydrilla- low density = native plant
Does Not Produce Toxins (e.g. golden algae)
Valued by the Fishing and Hunting Communities ► “ Fishing the Edge” “Ringneck duck buffet”
Growth Rate , Canopy formation, &
Ability to Occupy Vast Expanses ► Access, Flood Control, Fishery Mgmt.
► Native Plants, Water Quality
Increased water clarity
“Just leave us a little”
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Hydrilla Expansion
Initial Establishment – difficult step
2 to 10% may be the hardest step
Once well established plant can
easily go from 30 to >70% coverage
- widespread cover and low biomass !
Hydrilla creates habitat for more Hydrilla • Water clarification and wave reduction in open fetches
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Stignematalan algae – produces a novel toxin
Unintended Consequences
of Hydrilla Growth
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Kissimmee Chain of Lakes
– Headwaters- C&SF Flood Control Project
- Extensive hydrilla management
In a cruel twist of irony –
Florida DEP recently declared Lake
Toho impaired for Excessive
Macrophyte Growth (HYDRILLA)
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What Limits Hydrilla Growth ?
“It’s the light”, stupid
► Algal turbidity, suspended sediments
Poor Sediment quality or nutrition
Cyanobacteria blooms – toxins ?
Herbivores – general and specialists
► Grass carp, snails, etc.
Consistent Management ?
► Setting back the clock
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Unknowns for Hydrilla in MO
What is the greatest environmental constraint to hydrilla growth in MO waters ?
• Fluctuating Reservoirs
• Seasonal Extremes (temp, flow, etc.)
• Sediment Composition
• Water Clarity
Can hydrilla colonize & proliferate in MO Reservoirs ?
• We will likely find out
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