GUIDE TO WEED CONTROL 2016–2017 Publication 75
19. WATER WEEDS (AQUATIC PLANTS)
Ministry of Agriculture,
Food and Rural Affairs
19. WATER WEEDS (AQUATIC PLANTS)
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
available 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 and Climate Change
(MOECC) to perform a water extermination unless
exempt under the Regulation.
Subsection 82 and 83 of the Regulation provide
the authorization to perform water exterminations
Guide to Weed Control 2016–2017
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
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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 (e.g., 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 nondomestic 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 MOECC
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.
19. WATER WEEDS (AQUATIC PLANTS)
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 MOECC 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
Guide to Weed Control 2016–2017
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.
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
and Forestry.
Reducing or eliminating the flow of nutrients into
water bodies is an effective preventative measure
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19. WATER WEEDS (AQUATIC PLANTS)
TABLE 19–1. Herbicide Treatment Rates for Water Weeds (Aquatic Plants)
ACTIVE INGREDIENT
(rate)
TRADE NAME
(concentration)
PRODUCT RATE
PRECAUTIONS
For more information, see Chapter 4, Herbicides Used in
Ontario, page 27 and Chapter 5, Notes on Adjuvants,
page 81.
ALGAE AND VASCULAR SUBMERGENTS (e.g., Chara, Canada Waterweed, Coontail, Water Milfoil,
Bladderwort, Pondweed)
copper
(6.5–9 kg/m of water
depth)
diquat (aquatic)
(4.4–7 kg/ha)
POLYDEX BACTERIOSTATIC ALGAECIDE MC (5%)
1.6–16 mL/1,000 L • 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.
POLYDEX BACTERIOSTATIC ALGAECIDE (5%)
THINK PURITY ALGAECIDE SOLUTION (5%)
REWARD (240 g/L)
EMERGENTS
Rate depends on water depth:
• less than 1.5 m –
use 18.3 L/ha (7.4 L/acre).
• more than 1.5 m –
use 25–29.2 L/ha
(10.1–11.8 L/acre).
• 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 one-quarter to one-third of
the area at a time.
• Apply when plants are young and growing vigorously.
• Application to dense growth of mature weeds will not give
satisfactory control.
(e.g., Duckweed, Cattail)
acrolein (aquatic)
MAGNACIDE H (95%)
diquat (aquatic)
(4.4–7 kg/ha)
REWARD (240 g/L)
Guide to Weed Control 2016–2017
22 L/m3/sec–2,000 L/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.
Rate depends on water depth:
• less than 1.5 m –
use 18.3 L/ha (7.4 L/acre).
• more than 1.5 m –
use 25–29.2 L/ha
(10.1–11.8 L/acre).
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•
•
•
•
For control of duckweed.
Apply by directed surface spray on foliage.
Use in 1,700–2,200 L/ha (680–880 L/acre) water.
See REWARD note in previous section.
19. WATER WEEDS (AQUATIC PLANTS)
TABLE 19–2. Habitats and Herbicide Susceptibility of Common Aquatic Plants
LEGEND: VC = very common
C = common
I = infrequent
R = rare
S = susceptible
likely recover)
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.
– = Insufficient information available to make a rating
Plant
spring-fed
pond
dugout
I = intermediate
soft water
lake
(e.g., typical
hard water
lake
(e.g., typical
Muskoka
lake)
Kawartha
lake)
–
R = resistant (Weeds may be damaged but will
wet ditch
(contains
dry ditch
(contains
water at
time of
treatment)
no water
at time of
treatment)
–
–
VC
I
copper
compound
diquat
(Polydex)
(Reglone A)
–
–
S–I
–
S
R
mechanical
control
Algae
Pithophora
Spirogyra spp.
–
–
–
VC
VC
C–I
Ulothrix spp.
C
VC
–
–
VC
–
–
S
R
Mougeotia spp.
C
VC
–
–
VC
–
–
S
R
Cladophora spp.
VC
VC
C
VC
VC
VC
–
S
R
Muskgrass (Chara spp.)
VC
I
C–I
VC–I
VC
R
–
S
R
Stonewort (Nitella spp.)
I
R
VC
R
R
R
–
S
R
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
Eurasian water milfoil (Myriophyllum spicatum)
–
–
VC
Submergent Macrophytes
–
–
–
R
S
–
–
–
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
Water naiad (Najas flexilis)
–
I
–
VC
–
–
–
R
S
Canada waterweed (Elodea canadensis)
–
C
–
VC
–
–
–
R
I
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19. WATER WEEDS (AQUATIC PLANTS)
TABLE 19–2. Habitats and Herbicide Susceptibility of Common Aquatic Plants (cont’d)
LEGEND: VC = very common
C = common
I = infrequent
R = rare
S = susceptible
likely recover)
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.
– = Insufficient information available to make a rating
Plant
I = intermediate
soft water
lake
(e.g., typical
hard water
lake
(e.g., typical
R = resistant (Weeds may be damaged but will
wet ditch
(contains
dry ditch
(contains
Kawartha
lake)
water at
time of
treatment)
no water
at time of
treatment)
mechanical
control
I–C
spring-fed
pond
dugout
Muskoka
lake)
VC
VC
–
VC
VC
copper
compound
diquat
(Polydex)
(Reglone A)
M
R
R
Emergents
Cattails (T. latifolia, T. angustifolia)
Bulrush (Scirpus spp.)
–
–
C
VC
C
C
M
R
–
Sedge (Carex spp+A42)
–
–
C
C
C
VC
M
R
–
Bur reed (Sparganium spp.)
C
–
C
C
C
VC
M
R
–
Water plantain (Alisma spp.)
–
–
I
C
C
VC
–
R
–
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
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19. WATER WEEDS (AQUATIC PLANTS)
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