Aquatic Plant Management
Louis Helfrich, Ph.D.
Department of Fisheries & Wildlife Sciences
Virginia Tech
Plants: Problem or Benefit?
Photosynthesis by aquatic plants, both algae and rooted water
plants, represents the major source - contributing from 70 to 90%
of the dissolved oxygen. Aquatic plants can trap excessive
nutrients and detoxify chemicals. Aquatic wildflowers such as the
water lily are sold and planted to provide floral beauty in water
gardens.
Plants serve as nursery habitat and the foundation of the aquatic
food chain. They provide food, dissolved oxygen, and spawning
and nesting habitat for fish and waterfowl.
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Wildlife
Food
Nursery
Shelter
Critical
habitat
Too many plants! A weed is simply a very
successful competitor for space, light, and nutrients.
• Restricted
recreation
• Fish kills
• Fish flavor
problems
• Pond water odor
problems
• Drinking water
taste problem
• Stunted fish
growth
Why weeds? Nutrients, Light
Why weeds?
• Shallow water
• Clear water
• Excess fertility
(nutrients)
• Invasion of exotic
weeds
American Lotus, Nelumbo lutrea
Fertilization
Can you fertilize weeds away? No
Aquatic Weed Prevention
• Prevent fertilizer
runoff
• Prevent soil erosion
• Do not feed grass
clippings
• Do not feed fish and
ducks
• Fence livestock
• Steep banks
Aquatic plants can be divided into:
(1) algae
(2) rooted water plants.
Algae or Turbidity?
 Rooted aquatic plants are distinguished from the
algae by the presence of true leaves, stems,
roots, and flowers.
Common Floating Plants
Watershield
Spatterdock, Nuphar advena
Submerged Plants:Exotics
Emerged and Shoreline Plants
Cattail
Arrowhead
Plant Dominance
1.
2.
3.
4.
5.
6.
Algae
Turbid water
Fertile, P
Planktivourous, carp
Small zooplankton
Ducks & geese
1.
2.
3.
4.
5.
6.
Macrophytes
Clear water
Fertile, less P
Predators
Large zooplankton
No waterfowl
Weed Control Methods
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Watershed
management
Physical
Biological
Chemical
Weed Control: Physical Removal
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Drain
Dredge
Dragging
Raking
Cutting
Skimming
Harvesting
Aeration
Herbivorous animals
• Fish, geese, and swans
• Nutrient pumps
• Permits for exotic animals
Herbicides?
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Expensive
Short-term
Toxic
Registered
Liability
Dosage
Timing
Fish Kills
Water-use
restrictions
Chemical Control
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Algae
– Copper Sulfate,
– Copper Complex (Cutrine)
Submerged Weeds
– Diquat (Reward),
– Fluridone (Sonar / Avast),
– 2, 4-D, (Aqua-Kleen)
– Endothal (Aquathol K)
Floating (Duckweed and Watermeal)
– Diquat,
– Fluridone
Emergent and floating Plants
– Endothal, Fluridone, 2,4-D
– Glyphosate (Rodeo)
Application Timing
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Early spring
Actively growing
Cool water
Slow decay
Pickerel weed, Pontederia
Application Variables
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Area treated
Water depth
Water temperature
pH
Hardness
Flow Exchange
rates
• Weed density
• Weather conditions
• Suspended particles
Arrow Arum, Peltandra virginica
Chemical Control
• 1/3 of pond
at a time
• Follow label
• Observe
waiting
periods
Aquatic Problems
1.
2.
3.
4.
5.
Water weeds
Water quality
Muddy water
Leaking ponds
Nuisance
animals
6. Poor fishing
7. Fish kills
http://aquat1.ifas.ufl.edu/welcome.html
Control Methods For Aquatic Plants in Ponds and Lakes
Authors: L. A. Helfrich, R.J. Neves, G. Libey, and T. Newcomb, Extension Specialists, Fisheries and
Wildlife Sciences, Virginia Tech
Publication Number 420-251, posted March 2000
http://www.ext.vt.edu/pubs/fisheries/420-251/420-251.html
The density of aquatic plants (both algae and rooted macrophytes) is largely a
function of (1) nutrient concentrations (phosphorous and nitrogen) and, (2) light. In
general, nutrient-rich, shallow lakes experience greater nuisance water weed
problems than nutrient-poor, deep lakes.
Table 2. Waiting period (days) before using water after application of aquatic herbicides
(Helfrich et al. 1996).
Herbicide
Irrigation
Fishing
Livestock
Swimming
Drinking
Fluridone (Sonar)
30
0
0
0
0
Glyphosate (Rodeo)
0
0
0
0
2
Chelated Copper
0
0
0
0
0
Diquat (Reward)
5
0
1
1
3
Aquathal K
14
3
14
1
<25
Aquathal G
7
3
14
0
<25
Endothal
Giant Salvia, Salvinia molesta, exotic
Watershed Management
Why weeds? excess fertility
• Livestock waste
• Fertilizer runoff
• Waterfowl
Water Plant Control
http://www.ext.vt.edu/pubs/fisheries/420-251/420-251.html
• Watershed
management
• Physical
• Biological
• Chemical
– Water dyes
– Barley straw

Aquatic plants can be divided into (1) algae and, (2) rooted water plants. Algae are
primitive, simple plants which lack true roots, leaves, or flowers and reproduce by
spores, cell division, and fragmentation. They range in form from unicellular (single
cells), through colonial and filamentous types, to advanced forms which resemble the
higher aquatic plants. Some are microscopic, but impart green color to the water,
others are visible as surface films or bottom dwelling forms which are often confused
with higher aquatic plants.
High Diversity of Aquatic Plant Species
Pondweeds, Potamogeton spp.
Algae or Vascular Plant?
Chara Algae
Why water weeds?
Excess fertility!
• Livestock waste
• Crop fertilizer
• Ducks & geese
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Shallow water
Clear water
Bank slope
Exotic weeds
Physical controls
(1)
(2)
(3)
(4)
(5)
Water diversion
Dilution
Dredging
Deepening
Water level
manipulation
(6) Bottom sediment
covering
(7) Light elimination
(8) Harvesting
Barley Straw?
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The rate is 2-50 grams/square
meter
1 acre pond = 4046 m2 of water
Therefore, treatment of 1 acre
pond at the lowest recommended
dose, 2 grams would require 8092
grams or 17.8 pounds of straw.
Source: Aquatic Ecosystems 1877-347-4788. They charge
$55.00 for 11 pounds of barley
straw.
Minimum treatment for 1-acre
pond costs $110/acre.
Herbicide Selection
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Copper compounds
– algae
Flouridone (sonar)
– Submersed &
floating
Glyphosate (rodeo)
– emergent
2-4D
– submersed
Diquat
– algae & submersed