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Biology and Management

of Eurasian Watermilfoil

(Myriophyllum spicatum)

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Eurasian watermilfoil

Myriophyllum spicatum L.

Family Haloragaceae

Submersed plant forming surface mats, rooted to bottom, commonly grows in water from 0.3 to 5 m deep, occasionally deeper depending on water clarity

Native to Eurasia

Spread by boat trailers, human activity, wildlife

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Eurasian milfoil (Invasive Exotic)

- Rapid Canopy Formation – no native plants fill this niche

- Evergreen (PHS under ice) - bolts rapidly in the spring

- Bicarbonate use – efficient photosynthesis

- Not preferred by grass carp

- Spreads rapidly by fragments (boats, wildlife, harvesters)

- Native weevil has some impact, but is not predictable

- Where possible, drawdowns can be effective

- Herbicides are the most widely used option in glacial lakes

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Large Rootcrowns can

Survive Overwinter

Primed for rapid growth

in early spring

Dependence on recovery

From vegetative tissue

- can be a weak point in life cycle

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Prolific Seed Production –

Estimated – between 500,000

to 1 M seed heads/acre

- 12 to 24 seed heads per square foot

Up to 300 Million Seeds / Acre

Good viability

Seedlings – very fragile

Hybridity shows seeds are

important

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Coontail Eurasian Milfoil Variable Milfoil

Parrotfeather Cabomba

Limnophila

Bladderwort

Several Species with Similar Morphology

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Advanced Identification

Eurasian Hybrid Northern Typically – Genetic analysis < 14 Leaflets

4 Leaves per node

14 Leaflets (6-16) per node

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Significant Milfoil and Hydrilla Presence

A Large Area of the Eastern US – High Energy Reservoirs /

Turbid and high water level fluctuation

Reservoirs vs

Lakes

Cold Water North Temperate

J F M A M J J A S O N D

Bio

ma

ss (

g D

W m

-2)

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Warm Water North Temperate

J F M A M J J A S O N D

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W m

-2)

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Warm Water South Temperate

J F M A M J J A S O N D

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450

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EWM History via Literature

1950’s – Invasive traits in the Chesapeake Bay

►Patten 1956 – Notes on the Biology of M.

spicatum New Jersey Lake

1960’s - Large-scale control in Chesapaeke

Bay and TVA with 2,4-D

►TVA = 1.1 Million lbs of 2,4-D acid – 1962-69

►Large unexplained declines in Chesapeake(?)

Effectiveness of drawdowns

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EWM History

1970’s increased reports in inland lakes

►MI, WI, NY, NJ

►TVA and UW – several papers

►EWM in Canada

Numerous publications on “Milfoil Biology”

►Grace and Wetzel 1978, Aiken 1979

Additional focus on 2,4-D use

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EWM History

1980’s

►Sediments/Water Quality – invasive growth

►More 2,4-D

►Further concern in Canada and Pacific NW

1990’s

►Movement into Minnesota

►Invasions and Declines

►Milfoil Weevils

►Herbicide selectivity – fluridone/triclopyr

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EWM Literature 2000’s

►Low rate fluridone – whole-lake mgmt.

• MI, VT

►More research on Weevils

►Milfoil hybridity and implications for mgmt.

►More herbicide selectivity

• Early timing with auxin mimics

►Abiotic factors that influence growth (China)

►Milfoil/Management/Fisheries

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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 management strategies vary so

significantly? • State to State (rules/laws)

• Region to Region (problem)

Lakes vs. Reservoirs

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To Manage or Not to Manage ? While an Invasive Exotic, Eurasian milfoil (EM) does not

justify treating an entire aquatic system • Fisheries - EM provides beneficial habitat

• Ecologists - chemical disturbance > biological

EM is “now a naturalized citizen” (damage already done)

• EM is a symptom of the problem - nutrients

Proper Management Reduces EM and negative impacts • As an invasive exotic, EM is the problem

• Reduce EM and let native vegetation expand

Manage to Remove EM & Native Plants will Recover • Restore the system by removing the exotic plant

• Prevent spread to surrounding water bodies (Hydrilla – ME, WI)

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Managing Eurasian watermilfoil

Adirondack Park, NY (3000 water bodies) ► Hand-pulling via divers $385,000/year on Saranac

► Very limited use of herbicides

Maine DEP – ► No herbicides for milfoil control

► Hydrilla eradication w/herbicides for 6+ years

Idaho Dept. of Ag. ► 2008 – $2M Eradication program initiated - Herbicides

WA DOE ► Aggressive use of herbicides in select areas

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0 1,000 2,000 3,000 4,000500Meters

¹Dear IslandS. Gull Bay

N. Gull Bay

Eagle Island

Gilpin Bay

Pork Bay

Saginaw BayFish Creek Bay

Buck Island

Bottle Bay

Little Square Bay

Square Bay

Back Bay

")

")

")

")

")

")

")")

")

")")

")

")")

Adirondack Park

4200 acres

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3 Midwestern States – Different

Approaches to EWM Control

State Fluridone (whole-lake)

Liquid

2,4-D

15%

Littoral

Trmt . Rule

State

Matching

Grants

Fishery

/APM

Friction

MI

DNRE

Y (6+6 ppb)

N N N Y

MN DNR N N (state

grants)

Y (exceptions)

Y Y

WI DNR N Y N Y Y

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Which is the “Right Way” ?

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Classical Biological Control

-Most relevant question – will the organism

provide “a timely & desired level of control” - Some organisms are very consistent

- others are inconsistent

(Euhrychiopsis lecontei)

Alligatorweed and flea beetle Eurasian milfoil and weevil

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Mechanical Control - Little has changed in 30+ yrs

- Increased Milfoil Spread

Drawdowns -Effective on many species (winter)

-Effective for Milfoil control

-Reservoirs vs. Lakes

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At the end of the day, we treat

where people live,work, & play !

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Parrotfeather (Myriophyllum

aquaticum) • Non-native aquatic plant from

South America

• Brought to U.S. in the late 1800’s likely as an ornamental plant

• Has been, and continues to be, spread by the aquarium and water garden industries

• Plant providers in San Francisco used to plant parrotfeather in the drainage canals behind their stores to have readily available plants

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• Parrotfeather is heterophyllous

• Plants can grow emergent leaves and/or submersed

leaves

• May have implications for selection of control techniques

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Plant Description • Emergent leaves are greyish green, stiff and waxy, and

occur in whorls around the stem

• Submersed leaves are red to orange, in whorls larger than Eurasian watermilfoil

• Dioecious species, however only pistillate plants are found outside of its native range

• Staminate plants are rare even in native populations

• Seed production is not known to occur

• Reproduction is exclusively vegetative via fragmentation and stolons

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Parrotfeather forms an

extensive network of

adventitious roots

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Parrotfeather Impacts • Parrotfeather can impede

streams, ditches, and small water-bodies

• Impeding of runoff results in flooding of adjacent lands

• Increases flood duration and intensity

• Provides a refuge from predation for mosquito larvae

• Poses a threat to drinking water supplies in South Africa

Waterfowl Pond in Alabama

Irrigation Canal in Idaho. Tom Woolf

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Infestation near Lake, Mississippi ~ 0.20 acres (743 m2)

April 2006 January 2006

Impedes access to livestock

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Biology and Ecology • Parrotfeather will invade highly

disturbed sites with high nutrient availability

• Invasion will occur from eutrophic>mesotrophic>oligo-trophic waters

• Parrotfeather can survive well on water column nutrients

• Shallow habitats are more susceptible to invasion than deeper sites (10 ft)

Nitrogen

1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0

Me

an

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tal M

yri

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llu

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qu

ati

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m B

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g D

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ot-1

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0

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10

y = 19.345 - 18.311x + 5.022x2

r2 = 0.82

% Tissue Nutrients

0.10 0.15 0.20 0.25 0.30 0.35

0

2

4

6

8

10

Phosphorus

y = 15.072 + 85.315x - 145.075x2

r2 = 0.78

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Biology and Ecology Stolons - 40-95% total biomass

Starch allocation is greatest

(16.3%) in stolons

Roots stored less than 3.8%

starch

Low points in both biomass and

starch allocation occurred from

October to March

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2006 2007

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Management Recommendations

Management - exploit times of low energy reserves (fall and

winter), or remove emergent shoots to gain access to the

stolons and other submersed tissues.

► Herbicide applications are effective

► Water level manipulations are effective

Management activities that target only the emergent shoots

will not be effective at controlling this species

Management - dictated by use patterns of the infested water

body

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January

February

March

AprilMay

JuneJuly

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Septem

ber

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November

December

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1002006

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Peak Biomass

Peak Starch Content

Target Management

Target Management

Target Management

Target Management

• Parrotfeather is

probably still in Missouri

• Climate will support this

species

• Problematic infestations

will be limited to small

ponds and slow moving

streams where nutrients

are in abundance