BUILDING STRONG®

The Biology and Management of Hydrilla

Michael D. Netherland

US Army Engineer Research and Development Center

Gainesville, FL

BUILDING STRONG®

Does Hydrilla Pose a Greater

Threat to Missouri Waters

Than Other Invasive Plants ?

Hydrilla Eurasian Milfoil Curlyleaf Pondweed

BUILDING STRONG®

Overview Hydrilla

►Life history

►The “Perfect Weed”

► Invasion History

Factors Impacting Establishment & Spread ► Abiotic contraints

Control Methods

Feasibility of Eradication

BUILDING STRONG®

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

BUILDING STRONG®

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

BUILDING STRONG®

Why Plant Biology Matters ?

What is it about Hydrilla that

Allows it to Grow to Such

Abundance ?

6

BUILDING STRONG®

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

BUILDING STRONG®

Hydrilla

BUILDING STRONG®

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

BUILDING STRONG®

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

BUILDING STRONG®

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

12

BUILDING STRONG®

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

BUILDING STRONG®

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

BUILDING STRONG®

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

58

BUILDING STRONG®

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

BUILDING STRONG®

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 ?

BUILDING STRONG®

Management Options Are

Limited

18

Environmental Extremes

Grass Carp – SE Reservoirs Selective Biocontrol

BUILDING STRONG®

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

BUILDING STRONG®

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

BUILDING STRONG® 21

Thousands of Harvesters - Winter Biomass Control , FL

BUILDING STRONG®

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

BUILDING STRONG®

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”

BUILDING STRONG®

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

BUILDING STRONG® 25

Stignematalan algae – produces a novel toxin

Unintended Consequences

of Hydrilla Growth

BUILDING STRONG®

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)

BUILDING STRONG®

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

27

BUILDING STRONG®

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

BUILDING STRONG® 29