Aquatic Plant ManagementLouis Helfrich, Ph.D.

Department of Fisheries & Wildlife SciencesVirginia 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.

• 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

FertilizationCan 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. Algae2. Turbid water3. Fertile, P4. Planktivourous, carp5. Small zooplankton6. Ducks & geese

1. Macrophytes2. Clear water3. Fertile, less P4. Predators5. Large zooplankton6. No waterfowl

Weed Control Methods

• Watershed management

• Physical• Biological• Chemical

Weed Control: Physical Removal

• Drain • Dredge• Dragging• Raking• Cutting• Skimming• Harvesting• Aeration

Herbivorous animals• Fish, geese, and swans• Nutrient pumps • Permits for exotic animals

Herbicides?

– Expensive– Short-term– Toxic– Registered– Liability – Dosage– Timing– Fish Kills– Water-use

restrictions

Chemical Control • 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

• Early spring • Actively growing • Cool water • Slow decay

Pickerel weed, Pontederia

Application Variables

• 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. Water weeds

2. Water quality

3. Muddy water

4. Leaking ponds

5. Nuisance animals

6. Poor fishing

7. Fish kills

http://aquat1.ifas.ufl.edu/welcome.html

http://www.ext.vt.edu/pubs/fisheries/420-251/420-251.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

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.

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

Endothal        

Aquathal K 14 3 14 1 <25

Aquathal G 7 3 14 0 <25

Table 2. Waiting period (days) before using water after application of aquatic herbicides (Helfrich et al. 1996).

Giant Salvia, Salvinia molesta, exotic

Watershed ManagementWhy weeds? excess fertility

• Livestock waste• Fertilizer runoff• Waterfowl

Water Plant Controlhttp://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

• Shallow water• Clear water• Bank slope• Exotic weeds

Physical controls

(1) Water diversion(2) Dilution(3) Dredging(4) Deepening(5) Water level

manipulation(6) Bottom sediment

covering(7) Light elimination(8) Harvesting

Barley Straw?

• 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 1-877-347-4788. They charge $55.00 for 11 pounds of barley straw.

• Minimum treatment for 1-acre pond costs $110/acre.

Herbicide Selection

• Copper compounds– algae

• Flouridone (sonar)– Submersed &

floating• Glyphosate (rodeo)

– emergent• 2-4D

– submersed• Diquat

– algae & submersed