Publication 75, Guide to Weed Control 2012-2013
Chapter 19. Water Weeds (Aquatic Plants)

User Notice:

The information on this page can only be viewed properly in Internet Explorer 8 or higher. If you are using a lower version of Internet Explorer, a link to the PDF version can be found at the top right hand side of this page.

Water Weeds (Aquatic Plants)

Types of Aquatic Plants

Aquatic vegetation can vary widely; species include completely submerged plants such as Canada waterweed and algae; free floating plants such as water lilies; and emergent plants such as cattails and bulrushes. Many emergent plants will grow equally well on the moist shoreline or when their lower stems and roots are in water. Where these emergent species have taken possession of the shoreline, control measures must embrace that area as well as the water.

Stonewort and muskgrass are a gray-green to green plant-like algae, attached to the sediment, or free floating. In dense communities this plant-like algae has a very strong musk odour. It is brittle to the touch and will dry to a white powder upon removal from the water.

Tapegrass (wild celery) which is found in many recreational lakes, is resistant to all the currently recommended herbicides. It has long rubbery leaves and numerous short roots. Control is possible only by mechanical methods.

Aquatic Herbicide Controls

Under the Pesticides Act and Ontario Regulation 63/09 a person requires an Aquatic Vegetation exterminator licence to use a herbicide to control aquatic plants and a permit issued by the Ministry of the Environment (MOE) to perform a water extermination unless exempt under the Regulation.

Subsection 82 and 83 of the Regulation provide the authorization to perform water exterminations and prescribe the exemptions from requiring a water exterminator’s licence and/or permit for the performance of a water extermination.

Subsection 83(2) of the Regulation exempts a person from requiring an Aquatic Vegetation licence if he/she performs a water extermination in, on or over a portion of surface water that is located within the boundaries of premises owned or occupied by him/her (or his/her full time employer).

Subsection 83(3) of the Regulation exempts a person from requiring a permit to perform a water extermination if:

  • He/she performs a water extermination in, on or over a portion of surface water that is located within the boundaries of premises owned or occupied by him/her (or his/her full time employer), and,
  • the extermination is being done on a water body that is wholly contained on those premises and the water body does not discharge, directly or indirectly (other than by percolation) into any water or watercourse that is located wholly or partly outside the boundary of the premises.
A drainage ditch is defined in the Regulation as an artificial watercourse, added to the natural land drainage system, primarily to collect and convey water and that, for some period each year, does not contain moving water.

The use of pesticides in a drainage ditch to control plants that emerge from or float on the surface of the water as long as the drainage ditch does not contain moving water at the time of the extermination does not require a permit under the following conditions:

  • A licensed exterminator, or a farmer who has successfully completed the Grower Pesticides Safety Course (i.e., a qualified farmer) applying Class 3, 4, 5, 6 or 7 pesticides that are appropriately labelled for that use.
  • A person using Class 5, 6 or 7 pesticides that are appropriately labelled for that use.
  • A farmer using Class 4 pesticides that are appropriately labelled for that use.

Sale of Aquatic Herbicides

In Ontario, aquatic herbicides are classified as non-domestic pesticide products (Class 3 or 4). Licensed pesticide vendors may sell an aquatic herbicide only to those persons that possess the appropriate licence and/or permit or present a letter signed by the MOE Director under the Act confirming that the person presenting the letter is exempt from an exterminator licence and/or permit.

A person who holds an Aquatic Vegetation exterminator licence may purchase a Class 3 or 4 herbicide for aquatic plant control. However, as noted above, a permit is required unless the exterminator is performing a water extermination on premises he/she owns or occupies or on premises that are owned or occupied by his/her full-time employer and the extermination is being done in, on, or over surface water that is wholly contained on those premises and the water body does not discharge, directly or indirectly (other than by percolation) into any water or watercourse that is located wholly or partly outside the boundary of the premises.

In situations where a person is exempt from both the requirement for an Aquatic Vegetation exterminator licence and a permit (as described above) the person must obtain a letter signed by an MOE Director under the Act confirming that he/she is exempt from requiring an Aquatic Vegetation exterminator licence and present the letter to the vendor to purchase a Class 3 or 4 herbicide for aquatic plant control.
Qualified farmers can purchase Class 3 and 4 pesticides for use in their own agricultural operation. Therefore, the above noted licence and/or permit exemptions apply. Farmers who present a registration number under the Farm Registration and Farm Organization Funding Act, 1993, or a signed Farmer Self Declaration form can purchase a Class 4 pesticide for use in their own agricultural operation.


Non-chemical Control Methods

Management techniques for vegetation control in ponds include minimizing nutrient input, dredging excess sediment, logs and other organic debris, decreasing the surface to depth ratio and increasing the rate of pond turnover (flushing). Some aquatic plant and algae life should be accepted and tolerated as a vital component of a healthy ecosystem.

Reducing or eliminating the flow of nutrients into water bodies is an effective preventative measure to control excessive aquatic weeds. Herbicides only provide temporary control of nuisance aquatic vegetation. Alternate methods such as mechanical removal of submergent plants, dredging or substrate alteration of drainage ditches can provide longer-term control. Mechanical control measures may have an impact on fish habitat and therefore would require approval from the Ministry of Natural Resources.

TRADE NAME

(Concentration)

active ingredient

PRODUCT RATE
PER HECTARE

active rate per ha

PRODUCT RATE

PER ACRE

PRECAUTIONS

For more information, see Chapter 4, Herbicides Used in Ontario, page 27 and Chapter 5, Notes on Adjuvants, page 77.

Algae and Vascular Submergents

(e.g. Chara, Canada Waterweed, Coontail, Water Milfoil, Bladderwort, Pondweed)

POLYDEX BACTERIOSTATIC ALGAECIDE MC (5%)

or POLYDEX BACTERIOSTATIC ALGAECIDE (5%)

or POLYPRO (5%)

or POND WIZARD ALGAECIDE (5%)

or THINK PURITY ALGAECIDE SOLUTION (5%)

or THINK PURITY ALGAECIDE AND ODOUR CONTROL SOLUTION (5%)

or TRIANGLE BRAND COPPER SULPHATE CRYSTAL (25.2%)

 

Copper

1.6–16 mL/1,000 L

 

 

 

 

 

 

 

 

 

6.5–9 kg per metre of water depth

 
  • To control algae in ponds, lagoons, dugouts and potable water tanks.
  • Do NOT apply or allow discharge to lakes, flowing water or ponds with outflow.
  • This product is toxic to fish, aquatic invertebrates and plants.
  • Effective application rate depends on water condition and the extent of micro-organisms present.
    		•

    REWARD (240 g/L)

     

     

    diquat (aquatic)

    18.3 L/ha or

    25–29.2 L/ha

     

    4.4–7 kg/ha

    7.4 L/ac or

    10.1–11.8 L/ac
  • For control of coontail, Canada waterweed and pondweed in still or slow-moving water of farm dugouts, farm ponds, farm ditches, lakes and canals.
  • Treat dense populations of duckweed as submergent and apply as surface spray on foliage.
  • Chara (stonewort, muskgrass) are not controlled.
  • Do NOT use treated water for animal consumption or swimming for at least 24 hours.
  • Do NOT use for human consumption or irrigation for at least 5 days.
  • To avoid oxygen depletion, treat only 1/4 to 1/3 of the area at a time.
  • Rate depends on water depth:
  • – less than 1.5 m – use 18.3 L/ha (7.4 L/ac).
  • – more than 1.5 m – use 25–29.2 L/ha (10.1–11.8 L/ac).
  • Apply when plants are young and growing vigorously.
  • Application to dense growth of mature weeds will not give satisfactory control.

    • Emergents

    (e.g. Duckweed, Cattail)

    AMITROL 240 (231 g/L)

     

    amitrole

    37.5–45.75 L/ha

     

    9–11 kg/ha

    15–18.3 L/ac
  • Cattails in non-crop areas (roadsides, fencerows, ditch banks, drainage ditches).
  • After catkins are fully formed and up to frost.
  • Do NOT disturb sprayed plant.
  • Do NOT apply where water will be used for irrigation, drinking or other domestic uses.
  • Do NOT apply where water is not wholly confined to user’s property.
  • Apply at a spray volume of 1,000 L/ha (400 L/ac) water.
    		•

    Magnacide H (95%)

     

     

    acrolein (aquatic)

    22 L per m3/sec1 – 2,000 L per m3/sec1

     
  • For control of duckweed in irrigation canals.
  • Do NOT permit dairy animals to drink treated water.
  • Do NOT use where waters will flow into potential sources of drinking water.
  • Prevent the release of treated water from endangering fish in natural bodies of water and reservoirs.
    		•

    REWARD (240 g/L)

     

     

    diquat (aquatic)

    18.3 L/ha or

    25–29.2 L/ha

     

    4.4–7 kg/ha

    7.4 L/ac or

    10.1–11.8 L/ac
  • For control of duckweed.
  • Apply by directed surface spray on foliage.
  • Rate depends on water depth:
  • – less than 1.5 m – use 18.3 L/ha (7.4 L/ac).
  • – more than 1.5 m – use 25–29.2 L/ha (10.1–11.8 L/ac).
  • Use in 1,700–2,200 L/ha (680–880 L/ac) water.
  • See REWARD note in previous section.
    		•

    1 See instructions for calculating application rates in the Magnacide H Application and Safety Manual at www.bit.ly/magnacide.

    TABLE 19-1. Habitats and Herbicide Susceptibility of Common Aquatic Plants

     

    spring-fed pond

    dugout

    soft water lake*

    hard water lake**

    wet ditch***

    dry ditch****

    mechanical control

    copper compound (1)

    diquat (2)

    amitrole (3)

    Algae

    Pithophora

     

     

     

     

     

     

     

     

    S–I

     

    Spirogyra spp.

    VC

    VC

    C-I

     

    VC

    I

     

    S

    R

     

    Ulothrix spp.

    C

    VC

     

     

    VC

     

     

    S

    R

     

    Mougeotia spp.

    C

    VC

     

     

    VC

     

     

    S

    R

     

    Cladophora spp.

    VC

    VC

    C

    VC

    VC

    VC

     

    S

    R

     

    Chara spp. (Muskgrass)

    VC

    I

    C–I

    VC–I

    VC

    R

     

    S

    R

     

    Nitella spp. (Stonewort)

    I

    R

    VC

    R

    R

    R

     

    S

    R

     

    Submergent Macrophytes

    Sago pondweed (P. pectinatus)

    I

    C–I

     

    VC

     

     

     

    R

    S

     

    Curly-leaf pondweed (P.crispus)

    C

    VC

     

    VC

     

     

     

    R

    S

     

    Bassweed (P.amplifolius)

    R

    C

     

    C

     

     

     

    R

    I

     

    Richardson pondweed (P. richardsonii)

     

     

     

    VC–C

     

     

     

    R

    S–I

     

    Flat-stemmed pondweed (P. zosteriformis)

     

     

     

    C

     

     

     

    R

    S

     

    Other narrow-leaf pondweed (Potamogeton spp.)

    I

    C

    C

    VC–C

     

     

     

    R

    S

     

    Eurasian water milfoil (Myriophyllum spicatum)

     

     

    VC

     

     

     

     

    R

    VS

     

    Native milfoil (M. exalbescens and others)

    C

     

    C

    VC

     

     

     

    R

    VS

     

    Bladderwort (Utricularia vulgaris)

     

    C

     

    C

     

     

     

    R

    S–I

     

    Coontail (Ceratophyllum demersum)

     

    C

     

    VC

     

     

     

    R

    I

     

    Water stargrass (Heterantheria dubia)

     

     

     

    C

     

     

     

    R

    S–I

     

    Tape grass (Vallisneria americana)

    R

    I

    C

    VC

    R

    R

    M**

    R

    R

    R

    Water naiad (Najas flexilis)

     

    I

     

    VC

     

     

     

    R

    S

     

    Canada waterweed (Elodea canadensis)

     

    C

     

    VC

     

     

     

    R

    I

     

    Emergents

    Cattails (T. latifolia, T. angustifolia)

    VC

    VC

     

    VC

    VC

    I–C

    M

    R

    R

    S–I

    Bulrush (Scirpus spp.)

     

     

    C

    VC

    C

    C

    M

    R

     

    S–I

    Sedge (Carex spp+A42)

     

     

    C

    C

    C

    VC

    M

    R

     

    S–I

    Bur reed (Sparganium spp.)

    C

     

    C

    C

    C

    VC

    M

    R

     

    I

    Water plantain (Alisma spp.)

     

     

    I

    C

    C

    VC

     

    R

     

    S

    Pipewort (Eriocaulon spp.)

    R

    R

    C

    R

    R

    R

    M*

    R

     

     

    Arrowhead (Sagittaria spp.)

     

    C

     

    VC

    I–C

     

     

    R

     

     

    Pickerelweed (Pontederia spp.)

     

     

    VC

     

    I

    R

     

    R

     

     

    Water smartweed (Polygonium amphibium)

    I

    I

     

     

     

     

     

    R

     

     

    Water shield (Brasenia spp.)

     

     

    C

     

     

     

     

    R

     

     

    White water lily (Nymphaea spp.)

     

     

    C

    C

     

     

    M*

    R

     

     

    Yellow water lily (Nuphar spp.)

     

    C–I

    C

    C

     

     

    M*

    R

     

     

    Duckweed (Lemna spp.)

    R

    C

    I–R

    VC

     

     

     

    R

    S

     

    Duckmeal (Wolffia spp.)

    R

    C–I

    I–R

    VC

     

     

     

    R

    S

     

    VC – very common; C – common; I – infrequent; R – rare

    S – susceptible; I – intermediate; R – resistant.

    M – Manual or mechanical methods equally as effective as herbicides.

    M* – Manual or mechanical methods are generally more effective than herbicides.

    M** – Manual or mechanical methods are the only control measure currently available.

    # Bur reed is also very common as a submerged plant in ecotypes C and D.

    ^ Weeds denoted with an "R" may be damaged but will likely recover.

    * – A typical Muskoka lake is an example of a soft water lake.

    ** – A typical Kawartha lake is an example of a hard water lake.

    *** – A wet ditch contains water at time of treatment.

    **** – A dry ditch contains no water at time of treatment.

    (1) Copper compound (Polydex).

    (2) Diquat (Reglone A).

    (3) Amitrole (Amitrole 240).