Aquatic Herbicides
An overview of the herbicides permitted
for use in Region 8 aquatic applications
Aquatic Vegetation
Emergents -
Floaters - either rooted in soil –
lacking roots or leaves
roots not growing extend into air
in soil
Submergents - Immersed
rooted in soil - leaves Plants completely submerged
do not extend out of water - not rooted
Acre Foot
A measure of
WATER
1 surface acre in area
X 1 foot deep =
43,560 square feet X 1 foot =
43,560 cubic feet
Chelation
From “Chela” – a lobsterlike claw
When an ion is held to two other
non-metal ions in a ring
compound by coordinate bonds
Chelation
More simply – though less accurately
An ion held to - but not part
of - another chemical
compound
Copper Compounds
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Copper compound
formulations
Copper compounds summary
COMMON NAME
Copper compounds (all below are chelated compounds)
BRAND NAMES
Cutrine-Plus (0.909 lbs elemental copper/gal) – labeled
for use in AQUATIC SITES to control algae
Cutrine-Plus Granular (0.0366 lb elemental copper per lb.
formulated weight) - labeled for use in AQUATIC SITES to
control algae
K-Tea (0.8 lb metallic copper/gal) - labeled for use in
AQUATIC SITES to control algae
Copper compounds summary
MODE OF ACTION
Copper ion released after application is toxic to vegetation
Unfortunately, the copper ion concentration needed to kill
algae is only slightly lower than that which kills fish
Relatively slow release of the copper ion from these
formulations makes them slightly less risky than copper
sulfate that was used in the past
Copper compounds summary
SELECTIVITY
Selective; kills algae but not other aquatic
vegetation
Copper compounds summary
SOIL ACTIVITY AND MOBILITY
Not soil active
Copper is strongly adsorbed to clay and organic
matter
Copper compounds summary
PERSISTENCE AND BREAKDOWN
Remains in soil indefinitely; however, at
application rates used it is essentially
chemically inactive a short time after
application
Copper compounds summary
TOXICITY TO HUMANS AND WILDLIFE
Generally low in toxicity; rat oral LD50 is listed as 1,312
mg/kg for K=Tea and 1,930 mg/kg for Cutrine Plus
Due to the relatively slow release of copper ions by
these products, fish toxicity is fairly low; LC50 for bluegill
is 1.2 ppm for Cutrine Plus
Irritating to eyes and skin; Cutrine-Plus carries the
signal word DANGER due to the potential for it to
cause irreversible eye and skin damage
Copper compounds summary
APPLICATION TIMING
During the active growing season for algae copper
compounds should be applied early in the day on sunny
days when the water is relatively warm (at least 60o F)
Copper compounds summary
WEAKNESSES OR LIMITATIONS
Wear goggles or a face shield and rubber
gloves when handling Cutrine-Plus
Hard water interferes with the action of the
released copper ions and makes dose
calculation difficult
Copper triethanolamine complex (K-Tea) should
not be used where water pH is below 6
Copper compounds summary
WEAKNESSES OR LIMITATIONS
Some states require permits for application of
copper herbicide to water
Despite the eye and skin damage potential of
the concentrated formulations, there is no
waiting period after application for use as
drinking water or for swimming; both activities
may begin immediately after application
2,4-D
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2,4-D formulations
2,4-D summary
COMMON NAMES
2,4-D
BRAND NAMES
Aqua-Kleen (0.19 lb a.i./lb) – labeled for
AQUATIC use
2,4-D summary
NOTE
Many other 2,4-D products are available, with or without
other a.i.s in the formulation
Terrestrial application of 2,4-D may be made only with
prior approval of the Regional Forester, and often
products in this compendium are equally or more effective
without the toxicological concern raised by 2,4-D
Labels for products to be applied to terrestrial sites are
not included in this discussion
2,4-D summary
MODE OF ACTION
Growth regulator; causes plant tissues to
outgrow their ability to feed themselves
Absorbed by both leaves and roots, and
translocated to actively growing areas
Aqua-Kleen is a granular formulation which
sinks to the bottom of treated water areas
It is absorbed primarily through the roots
2,4-D summary
SELECTIVITY
Selective; see label for susceptible aquatic
plants
In terrestrial applications, grasses are tolerant
while trees and broadleaf weeds tend to be
susceptible
2,4-D summary
SOIL ACTIVITY AND MOBILITY
Soil active
Amine formulations are readily mobile in soil if
percolating water is present
Ester formulations are less mobile
2,4-D summary
PERSISTENCE AND BREAKDOWN
Short half-life, generally 1-4 weeks; breakdown
is by microbial action
2,4-D summary
TOXICITY TO HUMANS AND WILDLIFE
Moderately toxic; rat oral LD50 is 639 mg/kg;
formulated Aqua-Kleen’s oral LD50 4,050
mg/kg for male rats
Ester formulations can be highly toxic to fish
Animal studies have indicated possible
carcinogenicity
2,4-D summary
PRIMARY FORESTRY USES
Aquatic use is primarily to control water milfoil or
water stargrass in ponds
Little current use in Region 8; past use has been
primarily in combination with other herbicides
May be useful for broadleaf weed control in wildlife
openings or rangelands
Any terrestrial use of 2,4-D requires Regional Forester
approval
2,4-D summary
APPLICATION TIMING
Should be applied during periods of active growth
Do not treat an entire pond or lake at one time;
treat strips or quadrats and wait at least two
weeks before follow-up treatments are made so
as to avoid oxygen depletion resulting from
decomposition of dead plant material and
subsequent fish kill
2,4-D summary
WEAKNESSES OR LIMITATIONS
In general, other products are available which pose less risk
and are more effective
Fish kill can result from treating too large an area of aquatic
vegetation at one time
Some states have additional restrictions on the use of 2,4-D
Terrestrial application may be made only with Regional
Forester approval
Diquat
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Diquat formulations
Diquat summary
COMMON NAME
Diquat
BRAND NAMES
Reward (2 lbs a.i./gal) – labeled for
AQUATIC use
Diquat summary
MODE OF ACTION
Contact herbicide; rapidly absorbed by vegetation, but
not readily translocated
Diquat summary
SELECTIVITY
Nonselective
Effective in controlling most submerged
aquatic plants
Diquat summary
SOIL ACTIVITY AND MOBILITY
Not soil active
Strongly adsorbed to clay particles
Rapidly deactivated by muddy water
Also, degraded by water with low pH
Diquat summary
PERSISTENCE AND BREAKDOWN
Breakdown is primarily by photolysis, although
persistence is generally limited by adsorption rather
than chemical breakdown
When bound to soil diquat is very persistent – but is
biologically unavailable
Microbial degrade is limited and almost completely
stops once diquat adsorbs to vegetation
Diquat summary
TOXICITY TO HUMANS AND WILDLIFE
Moderately toxic; rat oral LD50 is 230 mg/kg;
for Reward it is 810 mg/kg
Relatively low toxicity to fish
However, dermal toxicity to mammals is generally
higher than oral toxicity, and care must be taken to
avoid dermal exposure
Diquat summary
APPLICATION TIMING
Should be applied when target plants are
actively growing
Diquat summary
WEAKNESSES OR LIMITATIONS
Due to risk associated with dermal toxicity, this product is a
poor choice if lower-risk products are effective on the target
species
Rapid plant kill can result in oxygen depletion in ponds,
which can cause fish kill
Diquat is rapidly inactivated when applied in muddy water
Do not allow swimming in treated areas for 24 hours
following treatment
Endothall
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Endothall formulations
Endothall summary
COMMON NAME
Endothall
BRAND NAMES
Aquathol (0.101 lb a.i./lb of formulation product) – labeled for aquatic
weed control in LAKES and PONDS
Aquathol K (3.0 lbs a.e./gal) - labeled for aquatic weed control in
LAKES, PONDS, and DRAINAGE DITCHES
Hydrothol 191 (2 lbs a.i./gal) - labeled for algae and aquatic weed
control in LAKES, PONDS, and DRAINAGE DITCHES
Hydrothol 191 (granular) (0.112 lb a.i./lb of formulation weight) -
labeled for algae and aquatic weed control in LAKES, PONDS, and
DRAINAGE DITCHES
Endothall summary
MODE OF ACTION
Interferes with RNA synthesis
Acts as a contact herbicide, with little
translocation
Endothall summary
SELECTIVITY
Nonselective
Generally used against submerged aquatic plants
Endothall summary
SOIL ACTIVITY AND MOBILITY
Some soil activity, although absorption is
primarily through leaf surfaces in aquatic
applications
Mobile in water
Endothall summary
PERSISTENCE AND BREAKDOWN
Broken down in both soil and water by
microbial action at rates which are dependent
on temperature and nutrient availability
Endothall summary
TOXICITY TO HUMANS AND WILDLIFE
Highly to moderately toxic, depending on formulation
Rat oral LD50 for technical endothall acid is 38 mg/kg; for
sodium salt, 182 mg/kg; for amine salt, 206 mg/kg
Formulated products have lower toxicities: rat oral LD50
for Hydrothal 191 granular is 1,540 mg/kg and for the
liquid it is 233 mg/kg
Dermal toxicity is higher than oral toxicity, so precautions
must be taken to avoid dermal exposure
Endothall summary
TOXICITY TO HUMANS AND WILDLIFE
Endothall is also an eye irritant, and inhalation of
vapors or dusts can cause irritation and injury
Generally nontoxic to fish at concentrations of
500 ppm or less
Hydrothol formulations are more toxic to fish
than Aquathol formulations
Endothall summary
APPLICATION TIMING
Apply when water temperature is 65
degrees or above, and plants are actively growing
Endothall summary
WEAKNESSES OR LIMITATIONS
Due to its toxicity, endothall should not be used
if other products are available which will
effectively control the target species
Granular formulations are preferred to liquids
due to reduced risk of dermal absorption
Fluridone
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Fluridone formulations
Fluridone summary
COMMON NAME
Fluridone
BRAND NAMES
Sonar A.S. (4 lbs a.i./gal) – labeled for aquatic vegetation
control in FRESH WATER LAKES, PONDS, RESERVOIRS,
and DRAINAGE DITCHES
Sonar SRP (0.05 lb a.i./lb of formulation weight) – labeled
for aquatic vegetation control in FRESH WATER LAKES,
PONDS, RESERVOIRS, and DRAINAGE DITCHES
Fluridone summary
MODE OF ACTION
Inhibits formation of carotenoid pigments
in leaves, allowing chlorophyll to be bleached
by sunlight and preventing plants from
synthesizing food
Fluridone summary
SELECTIVITY
Selective; generally used against submerged
aquatic plants
Most aquatic plant species are susceptible, but
a few (algae, many floaters, reeds, cattails, and
others) are not
Identification of target species is critical when
using this product
Fluridone summary
ACTIVITY AND MOBILITY
Strongly adsorbed to organic matter in soil and
in water; extremely limited soil-activity or soil-
mobility (leaches slowly in soil)
Mobile in moving water
Fluridone summary
PERSISTENCE AND BREAKDOWN
Broken down in water primarily by light, however
some breakdown by microorganisms and aquatic
plants
In soil primarily broken down by microbial activity
Persistence ranges from 21 days in water to 90
days in hydro-soils, depending upon light,
temperature and microbial populations
Fluridone summary
TOXICITY TO HUMANS AND WILDLIFE
Generally low order of toxicity; technical
fluridone has a rat oral LD50 >10,000 mg/kg
Slightly to moderately toxic to aquatic organisms
and fish; 96 hour LC50 values are 11.7 mg/L for
rainbow trout, 14.3 mg/L for bluegill, and 10 mg/L
for channel catfish
There are no restrictions on use of treated water
Fluridone summary
APPLICATION TIMING
May be applied before or during active
growth period for target vegetation as long as
the weeds are visible and water movement is
minimal
Fluridone summary
WEAKNESSES OR LIMITATIONS
· Does not control algae, rushes and several
other plant species as listed on the label
It also has little effect on most floaters and on
cattails
Fluridone summary
WEAKNESSES OR LIMITATIONS
Very expensive product, with cost of approximately $1,000/gal
Label rates require from 1 pint to 1 gallon of Sonar A.S. per
surface acre (depending on depth), to produce a concentration
of approximately 200 ppb; costs from $125 to $1,000 per acre
foot
While this concentration is necessary with moving water,
concentrations as low as 10-12 ppb have been proven effective
where treated water will stay in place for at least 60 days; this
reduces costs to the range of $7 to $50 per acre foot
Glyphosate
Glyphosate formulation
Details
Rotenone (a piscicide)
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Rotenone formulations
Rotenone summary
COMMON NAME
Rotenone (piscicide)
BRAND NAMES
Noxfish (0.15 lb a.i. + associated resins/lb formulated weight) –
RESTRICTED USE PESTICIDE labeled for the eradication of fish from
LAKES, PONDS, RESERVOIRS, and STREAMS
Nusyn-Noxfish ([0.05 lb a.i. + associated resins + 0.025 lb piperonyl
butoxide[/lb of formulated weight) - RESTRICTED USE PESTICIDE
labeled for the eradication of fish from LAKES, PONDS,
RESERVOIRS, and STREAMS
Rotenone summary
BRAND NAMES
Chem-Sect Brand Chem Fish Regular (0.10 lb a.i. + associated
resins/lb formulated weight) – RESTRICTED USE PESTICIDE labeled
for use to SURVEY FISH POPULATIONS IN FRESH OR SALT
WATER PROVIDED THERE IS NO INTENT TO CONTROL SUCH
POPULATIONS
Chem-Sect Brand Cube Powder Fish Toxicant (0.185 lb a.i. +
associated resins/lb formulated weight) – RESTRICTED USE
PESTICIDE labeled for the eradication of fish from LAKES, PONDS,
RESERVOIRS, and STREAMS (IMMEDIATELY ABOVE LAKES,
PONDS OR RESERVOIRS).
Rotenone summary
MODE OF ACTION
Interferes with oxygen uptake by gills and
suffocates fish
It is also a potent insecticide (not usable as such
under the labeling of these products)
Rotenone summary
SELECTIVITY
Non-selective; kills all types of fish plus insects
and many other aquatic organisms
Rotenone summary
SOIL ACTIVITY AND MOBILITY
Not soil active or mobile in soil
Highly mobile in moving water
Rotenone summary
PERSISTENCE AND BREAKDOWN
Moderately persistent
After use in lakes or ponds, a waiting period
of several weeks must be observed before
restocking is attempted, unless the rotenone
is neutralized
Rotenone summary
TOXICITY TO HUMANS AND WILDLIFE
May be highly toxic; dependant on species
Rat oral LD50 is 561 mg/kg for Nusyn Noxfish and 178 mg/kg
for Noxfish; but it has relatively high dermal toxicity, and a 4-
hour inhalation LC50 of 0.049 mg/l
It is highly toxic to fish
Labeling carries the “DANGER / POISON” signal words
Rotenone summary
APPLICATION TIMING
Timing is not critical; applications are
generally made during warm weather, mostly for
applicator comfort
Rotenone summary
WEAKNESSES OR LIMITATIONS
Water temperature, alkalinity, and turbidity may
affect the activity of the product
In flowing streams rotenone MUST be
neutralized with potassium permanganate as it
passes out of the treatment zone
Failure to properly neutralize rotenone in flowing
water will result in fish kills downstream
Rotenone summary
WEAKNESSES OR LIMITATIONS
Some formulations are flammable
Use of a respirator is required for applicators
Avoid skin contact or exposure to mists or vapor