1. Biology and Management
of Eurasian Watermilfoil
(Myriophyllum spicatum)
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2. 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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3. 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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4. 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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5. 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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6. Several Species with Similar Morphology
Coontail Eurasian Milfoil Variable Milfoil
Limnophila
Cabomba
Parrotfeather
Bladderwort
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7. Advanced Identification
Eurasian Hybrid Northern
Typically – Genetic analysis < 14 Leaflets
4 Leaves per node
14 Leaflets (6-16) per node
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8. Significant Milfoil and Hydrilla Presence
500
Biomass (g DW m-2)
Cold Water North Temperate
Reservoirs vs
400
300
200
100
0
J F M A M J J A S O N D
Lakes
500
Warm Water North Temperate
Biomass (g DW m-2)
400
300
200
100
0
J F M A M J J A S O N D
450
Biomass (g DW m-2)
400
350
300
250
200
150 Warm Water South Temperate
100
J F M A M J J A S O N D
A Large Area of the Eastern US – High Energy Reservoirs /
Turbid and high water level fluctuation
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9. 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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10. 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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11. 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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12. 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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13. 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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14. 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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15. Managing Eurasian watermilfoil
 Adirondack Park, NY (3000 water bodies) Back Bay
)
"
► Hand-pulling via divers $385,000/year on Saranac )
"
Square Bay
Little Square Bay )
"
► Very limited use of herbicides Adirondack Park
Bottle Bay )
"
Fish Creek Bay )
"
)
"
)
"
)
"
Buck Island
Saginaw Bay
Pork Bay
Eagle Island
 Maine DEP –
Gilpin Bay )
"
¹
)
"
)
" N. Gull Bay
Dear Island )
" )
" S. Gull Bay
Meters
0 500 1,000 2,000 3,000 4,000
► No herbicides for milfoil control 4200 acres
► 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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16. 3 Midwestern States – Different
Approaches to EWM Control
State Fluridone Liquid 15% State Fishery
(whole-lake) 2,4-D Littoral Matching /APM
Trmt . Rule Grants Friction
MI Y N N N Y
(6+6 ppb)
DNRE
MN DNR N N Y Y Y
(state (exceptions)
grants)
WI DNR N Y N Y Y
Which is the “Right Way” ?
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17. Classical Biological Control
Alligatorweed and flea beetle Eurasian milfoil and weevil
(Euhrychiopsis lecontei)
-Most relevant question – will the organism
provide “a timely & desired level of control”
- Some organisms are very consistent
- others are inconsistent
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18. 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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19. At the end of the day, we treat
where people live,work, & play !
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20. 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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21. Parrotfeather is as far north as British Columbia, Canada BUILDING STRONG®

22. • Parrotfeather is heterophyllous
• Plants can grow emergent leaves and/or submersed
leaves
• May have implications for selection of control techniques
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23. 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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24. Parrotfeather forms an
extensive network of
adventitious roots
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25. Parrotfeather Impacts
• Parrotfeather can impede
streams, ditches, and small
water-bodies
• Impeding of runoff results in
flooding of adjacent lands
• Increases flood duration and Waterfowl Pond in Alabama
intensity
• Provides a refuge from
predation for mosquito larvae
• Poses a threat to drinking water
supplies in South Africa
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Irrigation Canal in Idaho. Tom Woolf ®

26. Infestation near Lake, Mississippi ~ 0.20 acres (743 m2)
January 2006 April 2006
Impedes access to livestock
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27. Biology and Ecology
• Parrotfeather will invade highly 10
y = 19.345 - 18.311x + 5.022x2
disturbed sites with high 8
r2 = 0.82
nutrient availability
Mean Total Myriophyllum aquaticum Biomass (g DW pot-1)
6
• Invasion will occur from 4
eutrophic>mesotrophic>oligo- 2
trophic waters 0
1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6
Nitrogen
2.8 3.0
10
• Parrotfeather can survive well y = 15.072 + 85.315x - 145.075x2
r2 = 0.78
8
on water column nutrients
6
• Shallow habitats are more 4
susceptible to invasion than 2
deeper sites (10 ft) 0
Phosphorus
0.10 0.15 0.20 0.25 0.30 0.35
% Tissue Nutrients
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28. Biology and Ecology
 Stolons - 40-95% total biomass
2006 2007
Emergent Shoot
Starch (% DW)
8
 Starch allocation is greatest 6
4
(16.3%) in stolons 2
0
Submersed Shoot
Starch (% DW)
15
 Roots stored less than 3.8% 10
starch 5
0
Starch (% DW)
20
 Low points in both biomass and
Stolon
15
10
starch allocation occurred from 5
0
October to March
Starch (% DW)
8
6
Root
4
2
0
May
May
Nov
Nov
Oct
Apr
Oct
Dec
Jan
Feb
Apr
Jun
Aug
Sep
Jun
Aug
Mar
Dec
Jan
Feb
Sep
Dec
Jan
Jul
Mar
Jul
Time
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29. 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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30. 700
Peak Biomass 2006
600
• Parrotfeather is 500
Target Management Target Management
Mean Myriophyllum aquaticum
400
Total Biomass (g DW m-2)
probably still in Missouri 300
200
100
0
• Climate will support this 60
50
2007
species 40
30
20
• Problematic infestations
10
0
will be limited to small 100
Peak Starch Content 2006
80
ponds and slow moving
Mean Total Starch Content (g m-2)
Target Management Target Management
60
streams where nutrients 40
20
are in abundance 0
2007
4
3
2
1
0
y y h il y ne ly t r er er er
u ar ar rc Ap
r
Ma Ju Ju us be ob emb emb
an ru Ma ug tem ct
J eb A p O v c
F
Se No De
Month
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