HomeMy WebLinkAboutCity Manager's Herbicide Report 2019CF YOF
HOME OF PELICAN ISLAND
OFFICE OF THE CITY MANAGER
1225 MAIN STREET — SEBASTIAN, FL 32958
PHONE 772-388-8200 — FAX 772-581-0149
1)carlisle(a,citvofsebastian.or2 — www.citvofsebastian.or2
MEMORANDUM
To: City Council
Subject: Herbicide Treatments
On April 10 2019 City Council asked for a report on options to maintain the waterways and canals within
the City. City Council's direction was not to determine if Glyphosate was dangerous or if the City should
not use the products containing this chemical. The direction from Council was to evaluate the possibility of
additional and or alternative measures to aquatic vegetation control, to use Best Management Practices and
maintain the various flood -control systems that are in place in order to protect the residents in the event of
major storm events to the best extent possible and avoid potential flooding.
The City has permits from the Saint Johns River Water Management District for its waterways. The
conditions of those permits require the maintenance of the waterways to promote water discharges and the
prevention of exotic vegetation. The Storm Water Treatment Park is currently not in compliance with that
permit. The establishment of Brazilian Pepper and other non-native vegetation will need to be removed as a
condition of this permit. The permit requires annual inspections for invasive species and a plan to remove
them. The maintenance plan is required to be updated every five years. The main function of the park by
the agreement is for stormwater treatment and storage. All other uses are incidental to this use.
The overall drainage systems permit also requires the management of vegetation; the following is the
excerpt from the Florida Administrative code;
10.3.3.2 Applicants shall submit detailed plans describing proposed construction, establishment, and
management of mitigation areas. These plans shall include the following information, as appropriate
for the type of mitigation proposed.
(k) A management plan comprising all aspects of operation and maintenance, including
water management practices, vegetation establishment, exotic and nuisance species control, fire
management, and control of access;
(l) A proposed monitoring plan to demonstrate mitigation success;
(m) A description of the activities proposed to control exotic and nuisance species should
these become established in the mitigation area. The mitigation proposal must include reasonable
measures to assure that these species do not invade the mitigation area in such numbers as to affect the
likelihood of success of the project,
In 2013 the City reduced the use of herbicides by over 50 percent at the request of some residents. This has
allowed the overgrowth that is seen in our system today. Several residents at the time voiced concerns over
the removal of vegetation, including invasive species on the city's stormwater treatment ponds, canals and
water features. This has reduced the carrying capacity of these ponds and water conveyance systems. This
in turn has resulted in limited access to these areas for both regular maintenance and emergency repairs,
placing the system at risk of failure in the event of a major storm.
The challenges that the City is facing are 1) devising a comprehensive plan to alleviate the overgrowth that
has been allowed to expand unchecked, 2) maintaining the flood control measures to facilitate the water
control measures, and 3) maintaining community support for the required programs.
Alternative measures to aquatic and terrestrial vegetation control are listed throughout this report, which
were researched by the City Manager, with the underlying mindset of utilizing best management practices,
and protecting the City's residents. The alternative measures are numerous and differ greatly in their
methodology. Some aspects of these methods are appropriate for the City's needs, and some are not
applicable or feasible. Hence, after researching the various alternative measures, Staff recommends that a
combination of these be considered, for the management of both, aquatic and terrestrial vegetation within
the City. Staff further recommends that the City develop a capital improvement plan that will address the
sediment in the canals, the encroachment of vegetation and aquatic plantings to improve water quality,
aquatic habitat and shoreline stabilization.
Federal and State Law
There are regulations that the City must follow to apply any herbicide, chemical or pesticide. The product
by law MUST be labeled for the use it is being used for. In other words the City cannot make up chemicals
and solutions and apply them without being in violation of the law under Florida State Statutes 482 and
487.
Federal Law
The Environmental Protection Agency (EPA) regulates the use of pesticides in the United States under
the authority of two laws:
1. the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA)
2. the Federal Food Drug and Cosmetic Act (FFDCA)
No pesticide may be legally sold or used in the U.S. unless it bears an EPA registration number. If a
pesticide is registered, EPA imposes enforceable label requirements, which can include:
• maximum rates of application
• classification of the pesticide as a "restricted use" pesticide
• restrictions on use
It is a violation of Federal law for any person to use a pesticide in a manner inconsistent with its
label.
State Law
The Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) includes provisions for monitoring the
distribution and use of pesticides, and for imposing criminal penalties for violations. It is unlawful under
FIFRA to use a registered pesticide in a manner inconsistent with its label, to alter the label, or to distribute
any adulterated or misbranded product in commerce. FIFRA authorizes "cooperative enforcement
agreements" between the Environmental Protection Agency (EPA) and the states.
In 1978, the states (including Florida) were given primary enforcement responsibility for pesticide use
violations. In Florida, regulations of pesticide distribution, sale and use are accomplished through the
Florida Pesticide Law (Chapter 487 of the Florida Statutes). This law and associated rules of the Florida
Department of Agriculture and Consumer Services (FDACS) specifically address pesticide registration,
labeling requirements, applicator certification and penalties for violations.
Every year, the EPA issues national Consolidated Pesticide Agreement Guidance, which outlines the
national enforcement priorities and activities that every state must address under its enforcement
agreement. EPA also issues compliance monitoring strategies to help ensure consistency in enforcement
activities across the nation.
The following report from the University of Florida Institute of Food and Agricultural Science (IFAS) and
in cooperation with The Florida Fish and Wildlife Conservation Commission Invasive Plant Management,
provides an overview on information for herbicides (pesticides) labeled for use in Florida's treatment of
aquatic vegetation. Later in this report each one is reviewed for cost, use restrictions and pros and cons.
There are seventeen herbicide active ingredients (chemical compounds) approved for use in Florida waters
as of 2018. These active ingredients may be formulated and sold under various trade names, such as
Aquathol, Rodeo and Sonar. More than 100 different herbicide trade names are available among the 17
herbicide compounds for use in the FWC aquatic plant management program. They are applied directly to
the target plant or dispersed within the water for the purpose of treating invasive weeds. These formulations
are purchased and used by state, federal and local government agencies responsible for environmental
management and weed abatement. They are also used by environmental contractors, farmers and, in some
cases, homeowners. Permission in the form of a state permit may be legally required prior to herbicide
application depending on type of water body, ownership, aquatic species present, proximity and hydrologic
connection to other water bodies, amount of herbicides to be used, and other variables.
Annlving a time -release granular herbicide
According to the plant species being treated, the location, time of year, weather, water -oxygen levels, and a
host of other variables, aquatic herbicides may be applied directly to the plant, directly to the water, or to
the plant and water at the same time. On some occasions, environmental conditions may dictate that certain
herbicides are not permissible. It is up to the user to follow the herbicide use label that accompanies the
herbicide container and to follow it exactly. The herbicide's label is a legal document that provides
important information about the specific herbicide product that is used.
A registered pesticide is one that has been researched and approved by the EPA for uses that are specified
on the label and labeling. The EPA registration number must appear on all pesticide labels to confirm EPA
registration.
The label explains in detail:
• Which type of site may be legally treated with the herbicide (ex: lakes, flowing waters, canals,
reservoirs);
• How to use the herbicide;
• Which rates to use for specific plants and environmental situations;
• Precautionary statements relative to the herbicide's possible hazards;
• Specific first aid.
A separate document, the herbicide's Material Safety Data Sheet (MSDS), presents specific technical
information that is useful in the event of a spill or mistake. It includes hazardous ingredients, spill or leak
procedures, data on physical components, fire and explosion, reactivity, health hazards, and special
precautions.
Useful Terminoloav for Herbicide Use and Invasive Plant Manaaement
The following terminology is often used to describe herbicides, their proper use and expected outcomes.
This information can be obtained by reading the herbicide label, the MSDS, technical fact sheets, and
supplements provided by the herbicide manufacturer. The lethal plant dose is the amount of active
ingredient required to kill a plant, often measured in parts per million (ppm) or parts per billion (ppb).
• A contact herbicide causes injury to plant tissue where contact occurs; contact herbicides control
plants relatively quickly.
• A systemic or translocated herbicide is absorbed into the plant through the leaves, stems or roots
and translocated throughout the plant to kill it from the inside. Systemic herbicides control
plants less quickly than contact herbicides.
• Selectivity refers to the ability of a herbicide to kill certain types of plants without causing
significant injury to others. Herbicides can be selective (narrow -spectrum) or non -selective
(broad spectrum), based on the range of plants affected. Selectivity is also influenced by
factors including application rate, time, method of application, environmental conditions and
stage of plant growth.
• Liquid formulations contain active ingredients that are suspended in liquid. Liquid formulations
may be best for certain species of plants or certain management situations, such as areas where
water movement is slow, or where there are deep sediments.
• Dry formulations contain active ingredients that are mixed into dry, slow -dissolving pellets,
granules, or wettable powders. Pellets or granules make it easier to "time -release" herbicide
into the water or soil at the lethal dose rate. This is important especially in areas where water
movement might dilute liquid formulations.
• "Mechanism of action" is the actual biochemical site of herbicide; generally, an enzyme or co-
factor. In some cases, the actual site is unknown. See table below for mechanisms of action for
the 17 herbicide compounds registered for use in Florida waters. See the Weed Science
Society of America (WSSA) Summary of Herbicide Mechanisms of Action.
• "Mode of action" describes the symptoms that occur after herbicide application leading to plant
death.
• An algaecide is a substance used for the control of algae. There are several EPA -registered
algaecides approved for use in Florida waters.
• Half-life is the time it takes for the concentration of a compound such as a herbicide to be
reduced by half because of breakdown or deactivation of the molecule.
• Breakdown is the chemical transformation of a herbicide active ingredient into non -toxic
compounds. This can happen through hydrolysis (breakdown due to contact with water),
microbial breakdown (degradation from the action of microbes) and photolysis (breakdown
from the absorption of energy from sunlight).
General Information on Herbicides Reaistered for Use in Florida Waters
The following table lists the chemical name for the 17 classes of herbicides registered for use in Florida
waters by the EPA and Florida Department of Agriculture Consumer Services (FDACS). The table lists
each herbicide class, the types of plants (submersed, emergent, floating) most often controlled by that
herbicide in FWC management programs, the year the herbicide was registered by EPA and FDACS for
use in Florida waters, the herbicide mechanism of action (MOA), and the closely related Weed Science
Society of America (WSSA) resistance management grouping.
The mechanism of action (MOA) describes the biological processes that are disrupted by the herbicide.
These biochemical pathways control the growth and development of plants. When herbicides are applied,
these processes cannot be carried out and plant injury and death will occur. Classifying an herbicide's
MOA and WSSA Grouping provides crucial information on the possibility of a plant population developing
resistance to an herbicide MOA within a particular grouping after repeated use. For example: the over-
reliance (in acres and time) on one MOA for weed control in an agricultural system can increase the
probability of selecting for an herbicide -resistant population. With repeated applications, susceptible
individuals of a target weed species will die off while the numbers of resistant plants will continue to
expand. In time, the MOA will no longer control that species in that location. To prevent/mitigate herbicide
resistance, it is advised to rotate or combine herbicide MOAs to reduce the selective pressure applied by
any one product. There may be multiple products within an herbicide class (e.g. sixteen different
glyphosate products were applied in FWC-funded control programs in 2017) and there are several herbicide
classes with the same MOA (e.g. four ALS inhibitors) registered for use in Florida waters. Applying
different products or different herbicide classes within the same MOA does not constitute resistance
management. See Section 4 for a more detailed look into herbicide resistance.
Herbicide
Application Site
Year
Registered
Mechanism of Action
WSSA
Group
Copper
Submersed
1950s
Undefined
Undefined
2,4-D
Submersed, Emergent,
1959
Synthetic auxin
4
Floating
Endothall
Submersed
1960
Protein phosphatase inhibitor — PPl
Unknown
Diquat
Submersed, Emergent,
1962
Photosystem I inhibitor
22
Floating
Glyphosate
Emergent
1977
Enolpyruvyl shikimate-3-phosphate
9
synthase Inhibitor — EPSP
Fluridone
Submersed
1986
Phytoene desaturase enzyme
12
inhibitor — PDS
Peroxides
Submersed — algaecide
2002
Oxidize cell membrane
Triclopyr
Submersed, Emergent
2002
Synthetic auxin
4
Imazapyr
Emergent
2003
Acetolacetate synthase enzyme
2
inhibitor — ALS
Carfentrazone
Submersed, Emergent,
2004
Protoporphyrinogen oxidase enzyme
14
Floating _
_
inhibitor — PPO (Protox)
Penoxsulam
Submersed, Floating
2007
Acetolactate synthase enzyme
2
inhibitor — ALS
Imazamox
_
Submersed, Emergent,
2008
Acetolactate synthase enzyme
2
Floating
inhibitor — ALS
Flumioxazin
Submersed, Emergent,
2011
Protoporphyrinogen oxidase enzyme
14
Floating
inhibitor — PPO (Protox)
Bispyribac
Submersed, Floating
2012
Acetolactate synthase enzyme
2
inhibitor — ALS
p-Hydroxyphenyl pyruvate
Topramezone
Submersed
2013
dioxygenase enzyme inhibitor —
27
HPPD
Sethoxydim
_
Emergent — grass specific
2017
Acetyl CoA carboxylase enzyme
I
inhibitor — ACCase
Florpyrauxifen
Submersed, Floating,
2018
Synthetic auxin
4
Emergent
General information follows on each of the 17 classes of herbicides registered for use in Florida waters.
Specific use patterns and considerations for applying these compounds in aquatic plant management
programs are detailed in Section 4.
Bisinribac
Bispyribac has been labeled and used for weed control in rice for many years. It was registered by the
U.S. EPA and FDACS for aquatic plant control in 2012 and is sold under the trade name Tradewind.
Bispyribac's mechanism of action is an ALS enzyme inhibitor and is in the WSSA Resistance
Management Grouping #2. It is a systemic herbicide that is absorbed into and moves within the affected
plant. Bispyribac accumulates in the growth regions (meristems) of plants where it inhibits a plant -
specific enzyme called acetolactate synthase (ALS). When this enzyme is blocked, the production of
certain amino acids necessary for plant growth and development is stopped. The amino acid synthesis that
is blocked by bispyribac is specific to plants; this biochemical pathway does not occur in animals. The
plant stops growing and eventually dies over a long period of time — generally weeks to months. Like
most systemic aquatic herbicides, control is highly dependent on contact time or exposure of the plant to
the herbicide. The primary degradation pathway for bispyribac is microbial metabolism. The half-life in
water is about 30 days.
Bispyribac is most often applied in management programs to control hydrilla (Hydrilla verticillata). It is
applied alone via subsurface injection at 30-45 ppb and requires 60-90 days of exposure to achieve control.
With a half-life in water of about 30 days, monitoring and reapplication to sustain the original prescribed
dose and exposure period is required. Combining bispyribac at 30 ppb with 1.0 ppm potassium endothall
not only reduces the exposure time required to control hydrilla, but also provides a measure of resistance
management by applying two different mechanisms of action. Research with Bispyribac is still underway in
many areas, but the herbicide appears to offer selective control of submersed and a few floating aquatic
weed species.
Carfentrazone
Carfentrazone was registered for aquatic plant control in Florida waters in 2004. Its mechanism of action is
classified as a protoporphyrinogen oxidase (PPO) enzyme inhibitor and is listed along with flumioxazin in
the WSSA Resistance Management Grouping #14. Carfentrazone is a contact herbicide. It does not move
within the plant. It is absorbed through the leaves and inhibits the protoporphyrinogen oxidase enzyme that
is important in chlorophyll synthesis. Carfentrazone needs 1-2 hours of contact for good herbicidal activity.
It is fairly slow acting once inside the leaves, causing symptoms in 2-5 days and plant necrosis in about 3-4
weeks. It provides good selectivity in that it will not control comingled non -target plants like pickerelweed
or grasses that may be mixed with water lettuce. Carfentrazone breaks down both through microbial action
in soil and through hydrolysis with a half-life of 3-5 days in water. It has very low toxicity to fish and
waterfowl.
Carfentrazone has limited use in FWC management programs. It is primarily applied in combination with
imazamox directly to the leaves to control Uruguayan primrose complex (Ludwigia
grandiflora / hexapetala). While this combination may provide faster control, it is not confirmed if
carfentrazone adds long-term efficacy above imazamox alone. Carfentrazone is occasionally applied via
foliar applications to control water lettuce and sometimes water hyacinth.
Coaaer
Copper is a fast -acting, broad-spectrum, contact herbicide that kills a wide range of algae and aquatic
plants. Although copper is a micro -nutrient required by living plants and animals in small amounts, too
much copper kills plants by interfering with plant enzymes, enzyme co -factors, and plant metabolism in
general. The mechanism of action is undefined; however, copper -based products are believed to target
specific physiological processes, such as electron transport in photosystem I, cell division and nitrogen
fixation. Copper is not classified in the WSSA Resistance Management Grouping. Several environmental
factors influence bioavailability of copper in aquatic systems including: pH, alkalinity, hardness, ionic
strength, organic matter, and redox potential. Copper chelates are broken down by hydrolysis and rapidly
decline to ambient concentrations with a half-life reported from 2-8 days depending on conditions.
Copper has long been used in natural and industrial waters for algae control, often applied directly to
water as blue copper sulfate crystals. Today in Florida, chelated copper is most often used for aquatic
plant and algae management. Chelate is a chemistry term meaning combining a metal ion, in this case,
copper, with an organic molecule, triethanolamine or ethylenediamine. Chelated liquid copper products
reportedly remain in solution longer than copper salts (when applied to hard water). Copper that is in
solution (suspended in the water) for a longer time has greater effect on the aquatic plants and algae. All
copper formulations are considered highly toxic to mollusks and can be toxic to some species of fish at
relatively low doses, especially if the water has less than 50 ppm of carbonate hardness (soft water).
Levels of 1-5 ppm are toxic to fish, so copper is usually applied at concentrations of 1 ppm or less.
Toxicity generally decreases as water hardness increases. Chelated copper is also less toxic than copper
salts to non -target organisms.
Although different brands of copper are available for aquatic plant and algae control in Florida, the
chemistry and mechanism of action of each is similar. Because copper is an element, it will accumulate in
the sediments regardless of its bioavailability. The Florida Fish and Wildlife Conservation Commission
(FWC) only permits or funds the use of copper herbicides in waters when no alternative management
options are available. Most notably, FWC authorizes the use of copper herbicides to control aquatic plants
near potable water intakes where use of other herbicide compounds may be restricted. There are no
drinking water restrictions for copper herbicides when applied at label rates.
Diquat
Diquat is a fast -acting contact herbicide. It was first formulated in the mid-1950s and used in aquatic
plant control beginning in 1962. Its mechanism of action is a Photosystem 1 inhibitor and is classified in
the WSSA Resistance Management Grouping #22. Diquat is rapidly absorbed by plant leaves and
interferes with cell respiration, the process by which plants take in oxygen. Diquat interferes with
photosynthesis by forming highly reactive and toxic free radicals, such as peroxide and super oxide, in
plant cells. Plant tissues are killed too quickly to allow translocation to other parts of the plant. Diquat
kills the aerial portions of plants in 24-36 hours. Diquat is water soluble and diffuses rapidly through the
water, quickly absorbing into plant tissue. However, Diquat is also strongly cationic and has a positive
charge, so it quickly absorbs to and is tightly held by the negative charges of clay and peat. For this
reason, Diquat is ineffective in muddy waters because it binds to the suspended particles. Diquat becomes
inactivated in the water and breaks down slowly in sediments. Half-life in water is 1-7 days.
In FWC-funded programs, Diquat is mainly used to control invasive floating plants including water
hyacinth (Eichhomia crassipes), water lettuce (Pistia stratiotes), giant salvinia (Salvinia molesta) and
feathered mosquito fern (Azolla pinnata). Diquat is also applied alone or in combination with 2,4-D to
control Cuban club rush (Cyperus blepharoleptos). Diquat is relatively ineffective when used alone to
control hydrilla (Hydrilla verticillata). However, combining Diquat with chelated copper provides quick,
albeit temporary hydrilla control. A synergism has been reported between these two compounds, such
that hydrilla takes up more Diquat and copper when they are applied together than when equal
concentrations are applied separately. This is a good option for quick control to eradicate or contain small
pioneer populations, such as those around boat ramps. Diquat and copper are not often considered for
large-scale hydrilla control because repetitive treatments increase the amount of copper in the system.
Diquat is used in combination with potassium endothall or flumioxazin herbicides for small to moderate -
scale hydrilla control. In each case, the addition of Diquat provides more rapid and perhaps more
thorough hydrilla control, while introducing a second mode of action for herbicide -resistance
management. Resistance has been confirmed in Landoltia spp. (a duckweed species) in Florida after
repeated Diquat use.
Endothall
Endothall acid, first available as an aquatic herbicide in the 1960s, was originally used in agriculture as a
plant desiccant. Products that contain endothall are used primarily for control of submersed weeds as well
as filamentous algae. The active ingredient is relatively fast -acting and is formulated into two compounds
for aquatic use: a potassium salt (potassium endothall) and an alkylamine salt (amine endothall). Both
compounds are available in liquid and granular formulations. The mechanism of action for Endothall
herbicides is categorized as protein phosphatase inhibitor. Endothall is listed in the WSSA Resistance
Management Group "Unknown". Endothall resistance in hydrilla (Hydrilla verticillata) has been reported
in two Florida public waters after repeated use of the potassium salt formulation.
Endothall interferes with plant respiration and photosynthesis by disrupting plant cell membranes.
Endothall breaks down in water microbially and the half-life is approximately 5-10 days. Because
Endothall is fast -acting, it was long considered to function as a contact herbicide, but it is somewhat
mobile in plant tissues. Endothall is absorbed by submersed plants in lethal concentrations in 12-36 hours,
depending on the concentration applied. Endothall acid works by interfering with plant respiration,
affecting protein and lipid biosynthesis and disrupting plant cell membranes. It causes cellular breakdown
of plants within 2-5 days. Symptoms of plant damage, including defoliation and brown shriveled tissues,
will become apparent within a week of herbicide application. Plants will fall out of the water column
within 3-4 weeks after application.
Potassium endothall, normally used at rates of 2-3 ppm, is not toxic to adult fish, eggs or fry at rates of
100-800 ppm depending on fish species. Potassium endothall is used extensively in Florida's hydrilla
management program, since hydrilla's increasing tolerance to fluridone herbicide was confirmed in 2000.
FWC sponsored extensive research and operational monitoring with the University of Florida and U.S.
Army Corps of Engineers to develop new use patterns with Potassium endothall alone and in combination
with other herbicide active ingredients, including bispyribac, diquat, fluridone, penoxsulam and
topramezone. Objectives included improving cost-effectiveness and resistance management, increasing
selectivity, and reducing overall herbicide use. These objectives are more achievable when applying
Potassium endothall to large areas in cooler months (November — April), when hydrilla is actively
growing, but native submersed plants may be dormant. Cooler water slows microbial degradation of
Potassium endothall allowing lower rates (1.5 — 2.0 ppm) and providing a more thorough control of the
hydrilla standing crop. Killing the stems and root crowns slows hydrilla's ability to recover, forcing
regrowth to come from tubers, turions and fragments. Good results have been achieved for large-scale
hydrilla control using Potassium endothall in combination with bispyribac and penoxsulam, and for
smaller scale control when applied in combination with diquat.
In contrast to Potassium endothall, Amine endothall is 2-3 times more active on plants, but 200-400 times
more toxic to fish than the potassium salt. Laboratory studies have shown the monoamine salts are toxic
to fish at dosages above 0.3 ppm. The liquid formulation will readily kill fish present in a treatment site.
EPA approved label rates for plant control ranging from 0.05 to 2.5 ppm. In recognition of the extreme
toxicity of the alkylamine salt, Amine endothall is rarely used for aquatic plant control in FWC aquatic
plant management programs. When used, it is applied, usually to small areas and at very low rates, with
Potassium endothall for hydrilla and crested floating heart (Nymphoides cristata) control to increase
efficacy and to introduce a second active ingredient for herbicide -resistance management.
Flonwrauxifen
Florpyrauxifen-benzyl was registered by the U.S. EPA and FDACS for aquatic use in 2018.
Florpyrauxifen-benzyl represents a new mode of action for hydrilla management and offers unique
properties for aquatic plant control as a member of the arylpicolinate herbicide chemical family. It has
been assigned reduced risk status from U.S. EPA. It is practically non -toxic to fish and birds and has no
drinking, fishing or swimming restrictions. Florpyrauxifen-benzyl is a systemic herbicide with an affinity
for aquatic vegetation. It is classified in the WSSA Resistance Grouping #4; an auxin mimic. It absorbs
through leaves and shoots via foliar treatments or underwater tissues during in -water applications.
Following rapid uptake, the herbicide translocates in the xylem and phloem and accumulates in
meristematic tissues where it bonds with a specific target receptor (AFB5-Aux/IAA co -receptor). It
mimics the effect of a persistent high dose of the natural plant hormone auxin, causing over -stimulation
of specific auxin -regulated genes, which results in the disruption of several growth processes in
susceptible plants. Tissues which are undergoing active cell division and growth are particularly sensitive.
Susceptible plants become brittle and shatter within a few days after exposure. Plants exhibit reduced
growth, and ultimately turn chlorotic and necrotic, reaching a level of control within 1-3 weeks after
treatment.
The primary breakdown pathway for Florpyrauxifen-benzyl in water is by photolysis. The half-life in
shallow water is < 12 hours and 1-2 days in deeper water. Breakdown is slightly enhanced via hydrolysis
in waters > pH8. Very high turbidity or algal content may also subtly reduce Florpyrauxifen-benzyl
uptake by targeting aquatic weeds following in -water application due to the herbicide's strong binding
properties and thus merit the use of higher rates within the label range. Florpyrauxifen-benzyl is an auxin
mimic herbicide and is subject to the DACS organo-auxin rule — 5E-2.033 F.A.C. While having low
volatility, it should not be applied aerially in winds less than 2 mph or greater than 10 mph (see spray
drift management on product label). Due to its short half-life and rapid plant uptake, florpyrauxifen-
benzyl is recommended to be expeditiously applied in tight swaths for spot treatment of target submersed
plants. Consequently, minor dissipation is expected from treatment plots during in -water applications. It
is recommended that the herbicide manufacturer (SePRO) be contacted for site -specific use
recommendations.
Florpyrauxifen-benzyl is registered to manage a broad range of invasive plants that are prevalent in
Florida waters. Floating and emergent plants include water hyacinth (Eichhornia crassipes), floating heart
(Nymphoides cristata), and water primrose (Ludwigia spp.), Eurasian watermilfoil (Myriophyllum
spicatum), hydrilla (Hydrilla verticillata), and hygrophila (Hygrophila polysperma) are on the list of
submersed species. While collaboratively assessed in mesocosm and pond studies by the U.S. Army
Corps of Engineers, the University of Florida, and other state/university partners, as of mid-2018, there is
little operational experience for management in large systems because of the recent registration. Early
field evaluation/demonstration will proceed with florpyrauxifen-benzyl applied alone and in combination
with other herbicides including diquat, fluridone, imazamox, penoxsulam, and potassium endothall.
Flumioxazin
Flumioxazin was registered for aquatic use in 2011. It is a contact herbicide with the same mechanism of
action as carfentrazone and the onset of rapid injury is similar to other contact herbicides. However,
Flumioxazin has a broader spectrum of activity compared to carfentrazone. Flumioxazin is a
protoporphyrinogen oxidase (PPO or protox) enzyme inhibitor, listed in the WSSA Resistance
Management Group #14. It moves within treated leaves but does not translocate to other areas of the
plant. Once inside the plant cell, Flumioxazin inhibits the PPO enzyme. Through a series of cascading
reactions, cell membranes are destroyed by lipid peroxidation reaction. The result is cell leakage,
inhibited photosynthesis, bleaching of the chloroplasts, and cell death. Plant necrosis and death is rapid,
taking a few days to a week or two. In general, at least four hours of contact time is required for good
control of susceptible plants. The primary breakdown pathway of Flumioxazin in water is by hydrolysis
and is highly dependent on water pH. Under high pH values (> 9), Flumioxazin half-life in water is 15-20
minutes. Under more neutral pH values (7-8), half-life in water is around 24 hours.
Flumioxazin is applied in FWC programs to control a wide variety of aquatic weeds and algal species.
Submersed plants include hydrilla (Hydrilla verticillata) and cabomba (Cabomba caroliniana). Floating
water lettuce (Pistia stratiotes), duckweeds (e.g. Lemna and Spirodella spp.,), giant salvinia (Salvinia
molesta), watermeal (Wolf is spp.) and surface mats of some algae are susceptible to Flumioxazin. Label
application rate recommendations range from 200-400 ppb for submersed plants and 6-12 oz. per acre
applied as a foliar spray for floating plants. Flumioxazin use patterns are still being developed, but rates
as low as 2-4 oz. per acre foliar spray or 50 ppb submersed application are reported to be effective for
water lettuce control. Field evaluations have shown that surface and submersed applications of
Flumioxazin also provide good control of spatterdock (Nuphar spp.), waterlily (Nymphaea spp.) and
American lotus (Nelumbo lutea). Flumioxazin can be tank -mixed with other contact or systemic
herbicides to enhance control of emergent weeds like large flower primrose willow (Ludwigia
grandiflora) when used in combination with glyphosate, imazamox or auxin mimic herbicides.
Fluridone
Fluridone is a systemic herbicide, discovered in the mid-1970s and used for weed control in cotton.
Fluridone was later shown to be effective for the control of submersed plants and was registered by the
U.S. EPA and FDACS for aquatic use in 1986. Fluridone is a phytoene desaturase (PDS) enzyme
inhibitor listed in the WSSA Resistance Management Group #12. Fluridone is absorbed through the
leaves and then translocated to shoot and root tissues. It inhibits the synthesis of light -shielding
carotenoid pigments and allows ultraviolet light to destroy essential chlorophyll pigments. Without
chlorophyll, the plant is unable to photosynthesize. Shoot tips bleach pink or white, and the plant slowly
starves and dies. The primary breakdown pathway for Fluridone is through photolysis, although microbes
also degrade the molecule. The half-life in Florida depends on light intensity, but is usually 20 days or
longer. Fluridone half-lives of 7-10 days have been reported in Florida. This has been attributed to
enhanced microbial degradation in waters that have received repeated large-scale Fluridone applications
for hydrilla (Hydrilla verticillata) control. Fluridone does not accumulate in fish or zooplankton and does
not affect algae. It has a low toxicity to fish at typical treatment rates in Florida waters between 8 and 15
ppb. Fluridone is approved for use in waters at rates up to 150 ppb.
Fluridone is a broad-spectrum herbicide that controls a variety of submersed and floating plants, such as
duckweed and Salvinia species. It is formulated as both a liquid, and as slow or fast -release pellets.
Application rates for plant control are in the 8-15 ppb range. The exposure period for submersed plant
control is measured in weeks or months and hours or days for floating plants. Fluridone must be kept at
prescribed concentrations for at least 45-80 days for optimum long-term control of hydrilla. Even longer
exposure is required for mature plants with high carbohydrate reserves. Once applied, Fluridone can
break down or dissipate from the application zone via wave action or water currents. Periodic monitoring
and reapplications are essential to ensure the proper Fluridone concentration is maintained in the hydrilla
control zone, long enough to kill the hydrilla standing crop.
Resistance to this herbicide was confirmed at several research institutions in 2000 after repeated large-
scale Fluridone applications for hydrilla control in Florida from the late 1980s through the 1990s. This
was the first occurrence of resistance for a bleaching -type herbicide and the first for a plant species based
solely on somatic mutations. Hydrilla produces only asexually in Florida leaving no avenue for gene
recombination. Fluridone attacks only one gene location in hydrilla and several genotypes have been
reported in Florida, each with different Fluridone susceptibilities. Repeated Fluridone use effectively
removed the susceptible hydrilla genotypes, leaving the more tolerant plants to expand.
Once the mainstay of hydrilla control in Florida public waters, Fluridone is now used on a limited scale in
FWC management programs. Strategies using Fluridone have evolved due to the unexpected resistance
development. Pre -application bioassays are essential to determine each hydrilla population's current level
of Fluridone tolerance. Applying too little Fluridone is wasteful in that it will not control the target plant.
Applying too much Fluridone is not only wasteful, but it may also injure non -target vegetation in the
system.
Glvahosate
Glyphosate is a broad-spectrum herbicide used to control annual and perennial broadleaf weeds and
grasses, trees, and certain floating plants. It does not control plants that are completely submersed or have
most of their leaves under water, as it lacks activity in water. Glyphosate is a systemic herbicide that is
applied to the foliage and moves throughout the plant to cause damage. Its mechanism of action is an
enolpyruvyl shikimate-3-phosphate synthase (EPSP) enzyme inhibitor and is listed in the WSSA
Resistance Management Group #9. Glyphosate works by inhibiting the synthesis of specialized plant
amino acids. Without the ability to manufacture these essential components, plant death occurs slowly
over a period of 2-3 weeks. Animals do not produce these enzymes, explaining the very low toxicity of
this herbicide to animals. Visible effects on most annual weeds occur within 4-7 days (more on most
perennial weeds), and 30 days or more on most woody plants and trees. Glyphosate breaks down in water
microbially with a variable half-life reported from 12-60 days. It binds readily with soil or suspended
organic particles, effectively inactivating the chemical activity. Also, hard water (containing calcium or
magnesium cations) used to make up a spray solution may bind some of the Glyphosate in the mix tank
prior to application.
Glyphosate is used alone or in combination with diquat, flumioxazin, imazapyr, or 2,4-D to control a
wide variety of plants in FWC management programs. Invasive grasses include torpedograss (Panicum
repens), paragrass (Urochloa mutica), Tropical America watergrass (Luziola subintegra), and West Indian
marsh grass (Hymenachne amplexicaulis). Other plants include Cuban club -rush (Cyperus
blepharoleptos), cattail (Typha spp.), primrose willow (Ludwigia spp.) and floating islands of mixed
herbaceous and woody species. Glyphosate is most effective when applied to actively growing plants that
have not recently been mowed, grazed or otherwise disturbed. However, an effective management
strategy for torpedograss control is to burn off the standing crop to the soil surface and wait for regrowth
to expend the plant's carbohydrate reserves; applying Glyphosate alone or in combination with imazapyr
where appropriate to the actively growing leaves and stems. Selective management of plants using
Glyphosate is achieved only by careful application because, in general, glyphosate damages most plants it
contacts. Heavy rainfall or irrigation within 2 hours of application may wash away the herbicide,
requiring a repeat treatment; rainfall or irrigation within 6 hours of application may also reduce
effectiveness. There are an increasing number of Glyphosate-resistant weeds reported in agricultural
settings. While none have been reported in Florida for aquatic use, it is important to rotate or combine
herbicides with different MOAs to the extent possible when applying Glyphosate.
Hvdrogen Peroxide
Sodium carbonate peroxyhydrate is a granular or liquid substance registered by the U.S. EPA and DACS
for use in Florida waters in 2002. Peroxides are oxidizing agents and are unclassified under the WSSA
Resistance Management Grouping. Sodium carbonate peroxyhydrate is transformed into hydrogen
peroxide and sodium carbonate in the presence of water. Hydrogen peroxide is the active component and
works by oxidizing critical cellular components of the target organism and kills it. For example: in lipid
peroxidation, oxygen radicals react with unsaturated fatty acids in cell membrane phospholipids,
sequentially damaging them and killing the cell in a chain reaction. Oxygen radicals also react with other
fatty acids, nucleic acids, and proteins in a similar manner. Sodium carbonate peroxyhydrate rapidly
dissociates via hydrolysis into hydrogen peroxide and sodium carbonate. Hydrogen peroxide is further
degraded to water and oxygen while sodium carbonate is neutralized to sodium bicarbonate. The half-life
for this process is approximately eight hours. When applied according to label directions, no harm is
expected to birds or freshwater fish and invertebrates.
Products containing sodium carbonate peroxyhydrate are used in aquatic systems for control of
planktonic algae, especially blue-green algae (also known as cyanobacteria). They are also used for
controlling problematic algae in domestic water supply sources. The granular formulation has been
evaluated to control dense mats of the filamentous cyano bacteria, Lyngbya (now Microseira wollei) that
is becoming increasingly common in Florida's freshwater spring runs. Repeated applications of hydrogen
peroxide algaecides with amine endothall or copper have provided Microseira control in hydropower
reservoirs in neighboring states.
Imazamox
Imazamox was registered for aquatic use in 2008. Imazamox is a systemic herbicide that is applied to
plant foliage to control floating or emergent plants, or to the water for submersed plant control. The
WSSA identifies Imazamox mechanism of action as an acetolactate synthase (ALS) enzyme inhibitor in
Resistance Management Group #2. It works by stopping the production of three amino acids (isoleucine,
leucine, and valine) which, in turn inhibit the production of ALS enzymes and other proteins that are built
from these amino acids. Although the exact mechanism is not understood, when ALS is inhibited, plants
die. Animals do not produce these particular enzymes, so Imazamox has low toxicity to animals.
Imazamox is classified as practically non -toxic to fish and birds. Enzyme inhibiting herbicides act very
slowly. Imazamox is broken down in the water by photolysis and microbial degradation. Its half-life in
water is 7-14 days.
Imazamox is available in liquid and granular formulations. It must be applied to actively growing plants;
preferably early in the season to young plants with lower carbohydrate reserves. It absorbs rapidly into
plant tissues and growth of susceptible plants is generally inhibited within a few hours after application.
In this regard, it acts somewhat like a contact -type herbicide, requiring a short exposure period. However,
plant death is relatively slow. Meristematic areas become chlorotic after 1-2 weeks followed by general
chlorosis and death in 2-6 weeks. In Florida, the primary aquatic plant management uses of Imazamox
include foliar applications to control cattail (Typha spp.), wild taro (Colocasia escuelenta), Uruguayan
primrose willow complex (Ludwigia grandiflora / hexapetala), and water hyacinth (Eichhornia crassipes).
Imazamox may be applied alone or in combination with other herbicides like glyphostate or
carfentrazone. Applying Imazamox alone provides a measure of selectivity for comingled non -target
plants. Combining with glyphosate or carfentrazone results in more rapid and thorough control, but is
usually limited to monocultural stands of target plants or in areas where selectivity is not a concern.
Imazamox may provide up to a year of control of water hyacinth via root uptake from in -water
applications.
Imazainr
Imazapyr was discovered in the 1970s and first sold in 1984. It was registered by the U.S. EPA and
DACS for use in Florida waters in 2003. Imazapyr's mechanism of action is an acetolactate synthase
(ALS) enzyme inhibitor and it is listed in the WSSA Resistance Management Group #2. Imazapyr is a
systemic herbicide that is quickly absorbed by leaves and shoots. It moves to areas of new growth where
it shuts down plant growth almost immediately. In this regard, imazapyr acts like contact herbicide. It
prevents the production of the ALS enzyme, without which, the plant cannot continue growing and
eventually starves and dies. Susceptible plants become reddish at the growth tips within 1-2 weeks.
Control may take 2-6 weeks. Imazapyr breaks down by light and has a half-life in Florida waters of about
2-3 days. Imazapyr is practically non -toxic (the EPA's lowest toxicity category) to fish, invertebrates,
birds and mammals.
Imazapyr should be applied to plants that are actively growing. If applied to mature plants, a higher
concentration of herbicide and a longer contact time will be required. Imazapyr is applied alone or with
glyphosate in FWC management programs to control cattail (Typha spp.), tussocks (floating masses of
herbaceous and woody species), torpedograss (Panicum repens), Cuban club -rush (Cyperus
blepharoleptos), and woody species growing in water, such as melaleuca (Melaleuca quinquenervia).
Imazapyr is not recommended for control of any submersed aquatic species. Cautions on the label
regarding damage to non -target vegetation and lengthy irrigation restrictions must be carefully followed,
limiting Imazapyr use to rural settings where irrigation is not a consideration.
Penoxsulam
Penoxsulam was registered for aquatic use by the U.S. EPA and DACS in 2009. It is a systemic herbicide
that is applied to plant foliage to control floating or emergent plants, or to the water column for
submersed plant control. Penoxsulam's mechanism of action is an acetolactate synthase (ALS) enzyme
inhibitor. It is listed in the WSSA Resistance Management Group #2. Penoxsulam is a systemic herbicide
that is absorbed by foliar tissues and moves to areas of new growth. It inhibits the ALS enzyme that
regulates the production of essential amino acids in plants. When ALS is inhibited, plants die. Animals do
not produce these enzymes, so Penoxsulam has low toxicity to animals. Enzyme inhibiting herbicides act
very slowly. Control is highly dependent on contact time. For some species and circumstances, split or
multiple applications are necessary to keep the herbicide concentration at a prescribed level for 90-120
days for optimum performance. Penoxsulam is broken down primarily via photolysis and to a lesser
extent by microbes. Its half-life in Florida waters is about 2-4 weeks.
While Penoxsulam controls a variety of aquatic plants, its primary use in FWC management programs is
to control hydrilla (Hydrilla verticillata) and water hyacinth (Eichhornia crassipes). When Penoxsulam is
applied alone, it may require more than 90 days of exposure to control hydrilla. This usually necessitates
one or more subsequent applications after the initial treatment to sustain an appropriate dose for control.
Research and operational monitoring have demonstrated that applying Penoxsulam in combination with
potassium endothall provides several advantages over Penoxsulam alone. Resistance to ALS herbicides
has been reported in terrestrial plants and a second active ingredient assists in resistance management for
both herbicides. Combining with potassium endothall reduces the time necessary for Penoxsulam to be
exposed to hydrilla to about 7-14 days, reducing the effects of degradation and dissipation and the need
for additional applications to sustain appropriate Penoxsulam concentrations in the water column.
Applying these herbicides in combination requires less of each herbicide to control hydrilla and seems to
increase selectivity to conserve non -target native plants. Likewise, applying Penoxsulam in combination
with flumioxazin or carfentrazone has provided an effective water hyacinth management tool with
increased resistance management benefit over Penoxsulam alone.
Sethoxvdim
Sethoxydim is a foliar-applied selective herbicide used to kill and suppress annual and perennial grasses
with little to no impact on broadleaf plants. It is applied as a post -emergent herbicide and requires the
addition of an oil adjuvant or nonionic surfactant for maximum effectiveness.
Sethoxydim was discovered in the late 1970s, and first registered on soybean and cotton in the early
1980s. It was the first of a large group of postemergence herbicides in the chemical family
cyclohexanedione `DIMS', that selectively controls grasses in broadleaf crops. Sethoxydim is an amber -
colored, oily, odorless liquid. It is a General Use Pesticide (GUP) in EPA toxicity Class III; slightly toxic.
Products containing Sethoxydim bear the Signal Word WARNING on the label.
Sethoxydim is in the Class 1 Group of herbicides (lipid biosynthesis inhibitors). It is absorbed rapidly
through leaf surfaces, transported in the xylem and phloem, and accumulates in meristematic tissues.
Sethoxydim inhibits acetyl CoA carboxylase enzyme that prevents fatty acid production, leading to
failure of cell membrane integrity, especially in regions of active growth. Lipids are an important
component in cell division and plant growth. If plant cells cannot divide, the plant will die. This results in
a cessation of shoot and rhizome growth, leading to necrosis and death of shoot meristems and rhizome
buds, and ultimately plant death.
Sethoxydim is water soluble, does not bind readily with soils, and therefore has the potential to be
mobile. Rapid degradation, however, generally limits extensive movement of Sethoxydim in the
environment. It is degraded rapidly by microbes and through photolysis, and possibly by hydrolysis. The
half-life of Sethoxydim in the field ranges from 5 to 25 days. In water, Sethoxydim can be degraded by
sunlight within an hour. Sethoxydim is not highly volatile.
Symptoms include cessation of growth within 2-3 days after application; growing tissue in the nodes and
buds become necrotic, young leaves are first affected and turn yellow (within 1-4 wks) and then brown,
depending on growing conditions. Leaf sheaths become brown and mushy at or just above their point of
attachment to the node; older leaves show yellowing, light purpling and browning; susceptible plants are
typically dead within 2-4 weeks and those not completely dead may show excessive tillering.
Topramezone
Topramezone was registered for aquatic use in Florida waters by the U.S. EPA in late 2013 and Florida
DACS in early 2014. It is a systemic herbicide that is applied to the water column for submersed or
floating plant control, or directly to foliage of floating and emergent vegetation. Topramezone is the first
aquatic -registered herbicide belonging to the chemical class called pyrazolones. In sensitive plant species,
Topramezone inhibits the enzyme 4-Hydroxy-Phenyl-Pyruvat-dioxygenase (4-HPPD) leading to a
disruption of the synthesis and function of chloroplasts. Consequently, chlorophyll is destroyed by
oxidation resulting in bleaching symptoms of the growing shoot tissue (white or pink coloration) and
subsequent death of the above ground portion of the pant. Topramezone is listed in the WSSA Resistance
Management Group #27. Isolated resistance to 4-1HPPD compounds has been confirmed in terrestrial
species, but there is no evidence of resistance in aquatic plants. Topramezone breaks down via photolysis
with a half-life in water ranging from 4-6 weeks. Microbial degradation is a minor breakdown pathway
for Topramezone that may also adhere somewhat to suspended clay particles.
Topramezone is under evaluation to determine optimum exposure periods and concentrations for hydrilla
(Hydrilla verticillata) control. Generally, Topramezone is applied at 25-40 ppb and maintained at or near
the initial concentration for a minimum of 60 days. This requires monitoring and possible reapplications
to sustain a prescribed dose until the plants die. Applications are made to actively growing plants early in
the growing season before mature plants can build carbohydrate reserves, mat at the water surface, and
during times of slow growth and reduce the effectiveness of subsequent herbicide response. Applying
early in the growth stage reduces the amount of herbicide and the exposure period necessary to control
hydrilla. Topramezone is absorbed into the plant tissue and symptoms generally first appear in 7-10 days.
Water hyacinth (Eichhomia crassipes) has been controlled via root uptake of Topramezone in waters
treated for hydrilla control. Operational use is under evaluation for foliar and in -water applications to
control water hyacinth and water lettuce (Pistia stratiotes).
Triclopvr
Triclopyr has been widely used to control herbaceous and woody plants in non -cropland sites, forestry
and pastures. It was registered for aquatic use by the U.S EPA and DACS in 2002. Triclopyr is a systemic
auxin mimic herbicide and is listed in the WSSA Resistance Management Group #4. Triclopyr is
absorbed by foliage and translocates throughout plant tissues. It moves to areas of new growth and causes
a disruption in hormone levels, interfering with normal expansion and division of plant cells. It acts like a
growth stimulant in some plant tissues and a growth retardant in others. Symptoms include cupped leaves
and twisted stems. Vascular tissue becomes crushed, stopping movement of essential nutrients and
sugars. Plants essentially grow themselves to death. Photolysis is the primary breakdown pathway in
water. Triclopyr has a short half-life depending on season and water depth (e.g. 2.5 days in shallow water
during the summer to 14 days in deeper water in winter. Triclopyr does not bind strongly or absorb to soil
particles.
Triclopyr has been used extensively in Florida's upland, invasive plant management program for basal
and foliar applications to control Brazilian pepper (Schinus terebinthifolia). It is effective for controlling
emergent aquatic plants, some floating plants, such as water hyacinth (Eichhornia crassipes), and some
submersed aquatic weeds, such as Eurasian watermilfoil (Myriophyllum spicatum). However, it is only
occasionally applied in aquatic situations in Florida due to extensive irrigation restrictions of 120 days for
treated waters. Triclopyr is applied with glyphosate, 2,4-D, or imazapyr to control tussocks (mixed
floating masses of woody and herbaceous plants). It is also occasionally used to control primrose willow
(Ludwigia octovalvis or peruviana) via foliar or in -water applications with 2,4-D.
2,4-D
2,4-D, or 2,4-Dichlorophenoxyacetic acid, is the oldest organic herbicide registered in the U.S. It is
primarily used for weed control in food crops (grains, corn, sorghum, rice, sugarcane), turf, non -crop
areas and in certain aquatic environments. 2,4-D was first applied in Florida waters to control water
hyacinth (Eichhornia crassipes) in 1959. It is an auxin mimic herbicide listed in the WSSA Resistance
Management Group #4. 2,4-D is a systemic herbicide. It is absorbed by roots and leaves and then
translocates and accumulates mainly in the growing points of shoots and roots. 2,4-D interferes with the
plant's ability to maintain proper hormone balance. Plants undergo uncontrolled growth in some tissues
and halted growth in other tissues. The result is injury to the growing regions of the plant and then a
gradual death, usually within 3-5 weeks. Microbial degradation is the primary breakdown pathway for
2,4-D that has a half-life ranging from one to several weeks. The half-life is shorter in warmer months
and in waters to which 2,4-D has been previously applied, presumably where microbial activity is greater.
The two main formulations currently in use for aquatic sites in Florida are the liquid dimethylamine salt,
and the granular butoxyethyl ester. The granular formulations of 2,4-D sink to the bottom and slowly
release herbicide into the water. Granular 2,4-D is applied for the control of water milfoil
(Myriophyllum spp.), and for some floating -leaved species. In FWC management programs, the liquid
formulations of 2,4-D are mixed with water and sprayed onto the leaves of water hyacinth and other
broadleaf aquatic weeds including Cuban club -rush (Cyperus blepharoleptus) and primrose willow
(Ludwigia spp.) 2,4-D is applied alone or mixed with other herbicides like diquat, flumioxazin, or
glyphosate to improve efficacy or resistance management.
2,4-D is sometimes confused with "Agent Orange," a name given to the military's plant defoliant
mixture, which was created and used during the Vietnam War. During the manufacture of Agent Orange,
it became contaminated with a cancer -causing dioxin, tetrachlorodibenzo-p-dioxin, known as TCDD.
While 2,4-D is one of the components of Agent Orange, it is not Agent Orange. It does not contain
TCDD, nor has it been shown to cause cancer. After numerous lifetime feeding studies in rats and mice,
the U.S. EPA has classified 2,4-D as Class D compound — Not Classifiable as to Human Carcinogenicity.
There have been discussions on using what some call natural products. As noted earlier in this report, the
City cannot use any product that is not labeled for that particular use. The City cannot mix certain
ingredients and apply them as a homeowner can, without being in violation of Federal and State law.
The following products are listed for vegetation treatment:
Green Gobbler
The Green Gobbler is 30% Acetic Acid formula and is labeled for vegetation, cleaning and other
household duties. It is a burn down treatment in that it does not affect the roots and must be applied often.
It has the potential to cause severe burns, blindness and is highly corrosive. The manufacturer does not
recommend using this product for aquatic plants. It carries a WARNING label.
Avenqer
Avenger is an extract from clove oil, eugenol, citrus or D-Limonene. It controls weeds by destroying the
leaf cuticle or causing cell leakage that rapidly leads to death. Unfortunately, because these herbicides kill
only green parts of the plant they contact, they don't provide long-term control of weeds with extensive
root systems or underground storage structures, such as rhizomes, tubers, or bulbs. Thus, many treated
plants are able to recover. These products carry the CAUTION label, as they have the ability to cause
skin and eye irritation and may be toxic to aquatic organisms.
Mirimichi Green
Ammonium nonanoate is closely related to other salts of fatty acids known as soap salts. The active
ingredient is a C9 saturated -chain fatty acid soap salt. It represents 40.0% by weight of the end use
product. Ammonium nonanoate is a non -systemic, broad-spectrum contact herbicide that has no soil
activity. The Soap Salts RED (EPA-738-F-92-013, September, 1992), states that ammonium nonanoate is
slightly toxic to both warm water and cold water fish species, but is considered highly toxic to aquatic
invertebrates. The use of ammonium nonanoate following label directions should not result in serious
impact to aquatic invertebrates because it is not applied directly to water and undergoes very rapid
microbial degradation in soil.
Biological Control Approaches
In considering biological controls that may be available, the City Manager reached out to the Institute of
Food and Agricultural Sciences (IFAS) to determine what is available and if those that are available can
help in the removal of the vegetation. The following is the list of information that IFAS provided for
biological controls and the effectiveness of them. Keep in mind the State has released the biological
insects that were approved and permitted into the ecosystem. So the City does benefit from them, as they
become established throughout the State.
There are several approaches for using biological controls. An approach is chosen after considering the
target plant, its habitat, and the management objectives:
• Classical Biological Control: A biological control agent is imported into the U.S. after extensive
study. The organism, usually an arthropod or pathogen, is released into its new habitat to attack
the target weed. Classical biological control relies on subsequent generations of the biological
control agent to suppress the invading species over a long period of time. The classical
approach is the most common method of biological control.
• Non -classical Biological Control: This approach involves mass rearing and periodic release of
resident biological control agents (native or introduced) to increase their effectiveness. The
large number of agents is intended to immediately suppress the target plant. Although this type
of biological control is generally used with mass-produced plant pathogens, repeated releases
of some insects have occasionally been used to provide season -long control of a target weed in
areas where it is too cold for the insect to survive the winter.
• Adventive (or Fortuitous) Biological Control: Regulation of a pest population by a natural
enemy that has arrived from elsewhere without deliberate introduction. Several examples are
presented below.
The development of an effective biological control agent requires a significant amount of time and
money, involves international cooperation, and may produce unpredictable results. For instance, the
biological control agent may fail to reproduce and/or provide the desired control on the target weed.
However, the long-term benefits of an effective biological control agent can far exceed the development
costs. The results from a successful biological control agent last longer than most management techniques
and reduce the need for, or amount of, chemical, mechanical, and physical controls. It is believed that
successful biological controls save much time and money in aquatic and wetland plant management.
During the past 50 years, eighteen biological controls have been evaluated overseas, studied in
quarantine, and released in Florida and throughout the southeastern U.S. to control five invasive aquatic
plant species.
The following are examples of Biological Controls:
Alligator weed flea beetles (Agasicles hygrophila) were imported from Argentina and first released in
Florida in 1964; an example of classical biological control. A member of the Chrysomelidae family, the
insect consumes the leaves and parts of the stems of the aquatic form of alligator weed. This insect has
been the most effective of the three biological control insects imported to control alligator weed. The U.S.
Army Corps of Engineers cancelled all herbicide spraying against alligator weed three years after its
introduction. Still, the beetle is less effective in southern Florida because of its sensitivity to climatic
extremes.
Alligator weed thrips (Amynothrips andersoni) is native to Argentina and was first released in 1967. It is
the least known of the alligator weed biological control insects. Leaf damage by the thrips affects the plant
by stunting its growth. This insect is the only one of the three that successfully controls the terrestrial form
of alligator weed.
Alligator weed stem borer (Arcola (= Vogtia) malloi) is a small, brown moth from Argentina that was
released in 1971. The larvae mine inside the stem and cause the plant to wilt and die. This insect is capable
of migrating great distances and is the most cold -tolerant of the alligator weed insects. Control is most
effective when used in conjunction with the alligator weed flea beetle.
The following list includes insects that have the potential to control Brazilian Pepper, but none of them
have been issued a permit for release to date.
• Brazilian Peppertree Thrips, Pseudophilothrips ichini
• Brazilian Peppertree Sawfly, Heteroperreyia hubrichi
• Brazilian Peppertree Leaflet Roller, Episimus unguiculus
• Brazilian Peppertree Stem Boring Weevil, Apocnemidophorus pipitzi
• Brazilian Peppertree Leaf Galling Psyllids, Calophya spp.
The only insect currently causing some damage to Brazilian peppertree in Florida is the adventive torymid
wasp, the Brazilian peppertree seed wasp (Megastigmus transvaalensis), which attacks the drupes or
seeds. In recent years, this insect has been expanding its range throughout the Brazilian peppertree infested
area. Megastigmus transvaalensis was probably introduced accidentally into the USA from Reunion or
Mauritius via France in Brazilian peppertree seeds sold as spices in some food shops. In 2001, a detailed,
two-year study on the distribution and effect of M. transvaalensis on Brazilian peppertree in Florida
observed that up to 3 1 % of the drupes were damaged by the wasp during the major winter fruiting period,
and up to 76% during the minor spring fruiting phase.
Hvdrilla (Hvdrilla verticillata)
Worldwide surveys began in 1981 to search for an effective biological control agent for the submersed
plant hydrilla. Some of the earliest research studied snails and pathogens, which produced unsatisfactory
results. Currently, four insects and one fish have been released to control hydrilla, but only two of these
insects are established, and only one is commonly associated with hydrilla in the southeastern U.S. None of
the insects have been able to adequately control or stress rapidly increasing hydrilla populations, but the
fish has proven to be very effective. During the past 40 years, the FWC Invasive Plant Management Section
(formerly DEP Bureau of Invasive Plant Management) has spent nearly $7.5 million — more than half of its
research budget — to evaluate potential biological control candidates and release promising candidates that
have passed quarantine regulations. This research has included collaborations with the University of
Florida, US Army Corps of Engineers, and the USDA.
The hydrilla tuber weevil (Bagous aff nis) was discovered in India and Pakistan and released in the U.S. in
1987. The adult lays eggs on rotting wood and organic matter. After hatching, the larvae burrow into the
ground until they find hydrilla tubers. The tuber is destroyed as the insects feed on it. Hydrilla tuber
weevils are specific to hydrilla and therefore do not pose a threat to other aquatic plants. The weevils failed
to establish because they are only effective during drawdowns and Florida lakes are rarely dry.
The Asian hydrilla leaf -mining fly (Hydrellia pakistanae) was found in India and first released in the U.S.
in 1987. The larvae of the Asian hydrilla leaf mining fly, together with the species described below, burrow
inside the plant's leaves. Each insect destroys up to 12 leaves throughout its developmental period.
However, hydrilla has not been effectively controlled by these insects. Research efforts are underway to
mass -rear them to use in an augmentative biological control strategy.
Australian hvdrilla leaf -mining flv
The Australian hydrilla leaf -mining fly (Hydrellia balciunasi) was found in Australia and first released in
the U.S. in 1988. Although it has failed to establish on hydrilla in Florida, a small population of this insect
has persisted in East Texas following its release.
The hydrilla stem borer (Bagous hydrillae) was imported from Australia and released in 1991. The larvae
burrow into the submerged stems of hydrilla, causing them to fragment. This insect also failed to establish
as the stem fragments require a dewatered sandy shoreline for larvae to develop within stem fragments — a
rare situation in Florida waters.
The hydrilla miner (Cricotopus lebetis) is a midge that has been associated with hydrilla declines in
several Florida locations since 1992. Developing larvae mine the growing shoot tips of hydrilla, which
severely injures or kills them. The feeding damage alters the plant's architecture by preventing new hydrilla
stems from reaching the water surface. The life cycle of the hydrilla miner is completed in 1-2 weeks. It is
not clear whether the midge is an adventive species or native insect that adapted to hydrilla.
Adventive hvdrilla moth
The adventive hydrilla moth (Parapoynx diminutalis) from Asia probably entered the U.S. via the
aquarium trade. It was discovered feeding on hydrilla in Florida in 1976. The lifecycle of Parapoynx is
completed in 4-5 weeks. The moth was never approved for release, but large populations of hydrilla are
occasionally completely defoliated by the larvae. It was later found that the moth is not a hydrilla specialist.
Chinese grass carp
Chinese grass carp (Ctenopharyngodon idella), a fish from China, is one of the most effective biological
control agents for hydrilla and a number of other aquatic plants. The voracious herbivore prefers hydrilla
and 2-25 fish can completely control one acre of the plant. Unfortunately, the fish does not eat only hydrilla
and also will consume most submersed and emersed aquatic plants once hydrilla is depleted. Florida's
interconnected surface waterways make it nearly impossible to restrict the range of grass carp. Because of
the potential environmental damage caused by a breeding population of grass carp, a sterile "triploid" grass
carp can be produced by treating fertilized eggs with cold, heat or pressure. It is legal in Florida to use grass
carp for biological control with a permit from the Florida Fish and Wildlife Conservation Commission
(FWC). An efficient means of recapturing grass carp has not yet been developed and this limits the
feasibility of employing the fish as a biological control agent. Triploid grass carp are stocked at very low
rates (1-2 fish/acre) to control hydrilla in about 80 small Florida public waters (less than 500 acres in size
and relatively self-contained).
Chinese grass carp were originally imported and stocked into Florida lakes in 1972 as part of an
experimental effort to control hydrilla. When stocked in high enough numbers, the fish proved to be
extremely effective. However, when attempts were made to remove the fish, managers and biologists
discovered the carp's uncanny ability to outsmart virtually every type of fishing technique. Nets, hooks-
and -lines, electro-shocking, and poison baits were minimally successful, especially after the first attempts.
It soon became apparent that once released, grass carp were nearly impossible to remove. As of 2010 there
are still no easy ways to remove grass carp from a stocked lake.
Plants Preferred by the Grass Carp
Hydrilla
Hydrilla verticillato
Coontail
Ceratophyllum demersum
Muskgrass
Chara spp
Naiad
Najas spp.
Slender Spikerush
Eleocharis baldwini
Jointed Spikerush
Eleocharis interstincto
Permit Required
Plants Not Preferred by the Grass Carp
Water Hyacinth
Eichhornia crassipes
Water Lettuce
Pistia stratiotes
Water Lilies
Nymphaea odorata, N. mexicana
Torpedo Grass
Panicum repens
Hygrophila
Hygrophila polysperma
Cattail
Typha spp.
In Florida, only triploid grass carp are allowed and a permit is always required, even when stocking
privately -owned waters. Permits may be obtained by contacting the Florida Fish and Wildlife Conservation
Commission (FWC).
Grass Carp Considerations
Chinese grass carp are not selective about the plants they eat. Once their preferred plants are consumed,
they can eat every plant in a waterbody, including submersed, immersed, and floating plants. They've even
been observed wriggling out of the water to eat grasses along the shoreline.
At low stocking rates (two to five fish per acre), it can take from six to twelve months before plants
noticeably decrease in abundance. And because grass carp generally consume plants starting with the roots
instead of the leaves and flowers, their effectiveness is sometimes underestimated. When this happens,
people have been known to stock more fish into the lake. In some instances, this has resulted in "over-
stocking" and the unintended consumption of all plants, leaving the lake devoid of vegetation.
If grass carp are stocked in high enough numbers, there is the potential for a lake to change from a Clear-
water, plant -dominated system to a murky, algae -dominated system. This happens when macrophytes
(larger plants) are consumed by grass carp, and algae (phytoplankton) expand to become the dominant
plants within the system. Within weeks or months, the water clarity can be significantly reduced as algae
increase in number and are suspended in the water. This gives the water an opaque, green color and can
appear as a scum on the surface of the water. Aquatic plants also serve as stabilizers for bottom sediments.
Once they are removed, there is increased potential for sediments to become disturbed and re -suspended in
the water, further decreasing clarity. This dynamic is sometimes overlooked and, as a result, there have
been disappointed lakefront homeowners over the years.
Grass carp can live for 10 years or more. The older they are, the larger they become and the more food they
will consume. If high numbers of fish are stocked, this can translate into the loss of a tremendous amount of
plant biomass within a lake.
The City tried Grass Carp and the project was not successful. The biggest challenge is the way the system
outfalls into the Sebastian River. There is not a feasible way to restrict the Grass Carp and keep them
contained within the system, so permitting would not be approved for them. Finally, the plants that are
needed to be addressed the most, are ones that the Carp do not consume.
Water hvacinth (Eichhornia crassibes)
Three biological control insects have been imported, studied, and released to control invasive water
hyacinth, a floating macrophyte that was introduced to the U.S. during in the late 1800s. Together, these
insects reduce the size and vigor of water hyacinth, and reduce flower and seed production. Individually,
however, they are not able to control water hyacinth.
The mottled water hyacinth weevil (Neochetina eichhorniae) was first released in 1972. The adults feed
on the leaves and petioles of water hyacinth, where they produce characteristic feeding scars. The larvae
tunnel in the petioles and crown of the plant. The mottled water hyacinth weevil has been the most effective
biological control insect for water hyacinth. It is able to stress plants, reduce flowers and seeds, and reduce
plant vigor.
The chevroned water hyacinth weevil (Neochetina bruchi) is very similar to N. eichhorniae. It was first
released in 1974. Both weevils reduce plant vigor and seed production and are damaging to young water
hyacinth stands. Studies have shown a substantial decrease in plant growth when the insect is used in
conjunction with herbicides. The weevils are unable to effectively control plants growing in water bodies
with high nutrient loads (e.g., at wastewater treatment facilities); the plants simply outgrow the effects of
herbivory.
The water hyacinth moth (Niphograpta (=Sameodes) albiguttalis) was first released in 1977. The larvae
feed by tunneling into the petioles of the younger, bulbous form of water hyacinth. The moth has been less
successful as a biological control agent because it disperses rapidly, has patchy distribution, and may be
completely excluded by the weevils on the older, non -bulbous plants.
The water hyacinth planthopper (Megamalus scutellaris) was released in Florida in 2010. Both the
nymphs and adults feed on the sap of water hyacinth, and the females deposit eggs into the leaf tissue. The
insect's population increases rapidly, which enables it to quickly impact water hyacinth. Nymphs are active
and readily hop off the plant if disturbed. Because of its mobility, this insect may integrate better with
existing maintenance control programs utilizing herbicides.
Water hyacinth mite (Orthogalumna terebrantis) is an arachnid native to the U.S. In high numbers, these
mites can desiccate water hyacinth foliage and cause leaves to turn brown. Severe damage may occur in
small areas, but rarely does this mite attain high enough populations to provide area -wide control of water
hyacinth.
Water lettuce (Pistia stratiotes)
Two South American insects have been released in Florida to combat water lettuce. Only one of these
insects is established, but it has not adequately controlled or stressed the plant populations in most
situations.
The water lettuce leaf weevil (Neohydronomus affinis) was imported from South America after showing
promising results as a biological control agent in Australia and South Africa. It was imported to the U.S. in
1986 and 1988. Two years after its release, the weevil population increased and effectively suppressed
water lettuce at several sites. It is now established and distributed widely throughout the state, but rarely
suppresses water lettuce growth. Adults and larvae feed on the leaves, crown and newly emerging shoots,
and the characteristic holes in leaves indicates high weevil densities. Feeding by multiple larvae destroys
the spongy leaf bases, which causes plants to lose buoyancy. The life cycle of the weevil is completed in 3
to 4 weeks. The weevil has not contributed to long-term suppression of the plant in the U.S., but has
provided successful biological control of water lettuce in other countries. It is thought that the weevil is
heavily preyed upon by imported fire ants in Florida. If true, this provides an interesting example of an
exotic insect controlling a valuable potential biological control agent.
The water lettuce leaf moth (Spodoptera pectinicornis) is native to Southeast Asia and was imported from
Thailand. The caterpillar was first released in Florida in 1990, but failed to establish. Fire ant predation also
may have prevented establishment of the moth. In its native range, augmentive releases of the moth have
been successfully used to control water lettuce in rice paddies.
Common and qiant salvinia (Salvinia spp.)
A tiny, black weevil, Cyrtobagous salviniae, is the only insect that has been released as a biological control
agent of giant salvinia (Salvinia molesta). Adventive weevils of one biotype that were discovered in
Florida in 1960 are used to control common salvinia (Salvinia minima), whereas weevils of another
biotype released in 2001 from a Brazilian population are used as biological control agents for giant salvinia.
Adult salvinia weevils (Cyrtobagous salviniae) feed on leaf buds and leaves. Larvae tunnel inside the
plant, killing leaves and rhizomes. The entire life cycle of the Cyrtobagous weevil takes approximately 46
days. Attacked plants turn brown and eventually lose buoyancy. Cyrtobagous weevils from Australia are
currently of great interest to researchers and have been introduced as a biological control agent for giant
salvinia in the U.S. The effectiveness of these weevils for controlling salvinia in the U.S. was recently
confirmed in Texas and Louisiana.
Other biological controls studied in the past include some snails that feed on several species of aquatic
plants, but have not proven effective as biological control agents.
Research, implementation, and results of biological controls are slow. Therefore, it is important to explore
other control methods, such as chemical, mechanical and physical, while establishing new biological
control agents. Protocols for integrating biological control agents with other control practices must also be
developed.
Livestock
The goal of prescribed grazing for invasive plant management is to manipulate patterns of defoliation and
disturbance to place a target plant at a competitive disadvantage relative to other plants in the community
(Walker et al. 1994). Achieving this goal requires extensive knowledge and solid understanding of how
invasive and desirable plant populations within a particular ecosystem will respond to a particular
herbivore's grazing behavior.
Not all ecosystems are compatible with grazing. Plant communities in two different ecosystems may
respond very differently to the same grazing prescription. Likewise, grazing patterns and their influence on
plant communities vary with different types of herbivores.
Grazing Management Tactics
In weed -infested areas, grazing must be carefully managed to reduce rather than increase invasive plant
establishment and spread. Ecologically -based grazing prescriptions pay careful attention to positively
directing plant community change, not just removing the weedy species (Sheley et al. 1996). Grazing
prescriptions may put target plants at a competitive disadvantage using two general approaches (Frost and
Launchbaugh 2003):
Use grazing management that harms the target plant species by grazing at a time and frequency
when the target plant is most vulnerable.
2. Modify the grazing behavior of animals to cause them to concentrate their grazing efforts on the
target plant instead of the desirable vegetation.
Prescribed grazing tactics manipulate three basic variables —herbivore selection, seasonal timing, and
intensity to cause a predictable plant community response.
Herbivore Selection
Selecting an appropriate herbivore is an important step in designing a grazing prescription. Cattle, sheep,
goats, and other livestock animals have different dietary preferences, foraging behaviors, and management
requirements. Just as herbicides and biological control agents are specific to groups or species of plants,
livestock animals are selective in which plants they eat, and how they eat them. Furthermore, livestock
animals require access to water, protection from predators, and have variable needs in terms of containment
and herd management.
i
Common Livestock Animals
Diet
Behavior
Care
Other
grazers
Goats
prefer browse
(woody plants),
then forbs
most tolerant of
secondary plant
compounds
narrow, strong
mouths designed
for stripping
individual leaves
and chewing
branches
can reach taller
branches by
standing on hind
legs or climbing
do not graze
uniformly
require herding, or
can be tethered to
concentrate
grazing activity
temporary,
portable fencing is
sufficient for
containment
Sheep
prefer forbs, then
grasses
tolerant of
secondary plant
compounds
narrow muzzle
allows for
selective grazing
Cattle
prefer grasses
least tolerant of
secondary plant
compounds
foraging is less
selective than
sheep and goats
do not graze graze more
uniformly uniformly than
sheep or goats
require herding
temporary,
portable fencing
is sufficient for
containment
larger animals
potentially have
greater physical
impact than
sheep or goats
require periodic
movement, but
do not require
herding
require stable
fencing
less susceptible
to predation than
susceptible to sheep or goats
predation
horses can be used to control invasive grasses, but tend to be
more selective than cattle (Tu et al. 2001).
susceptible to
predation
geese have been used to control invasive grasses (Wurtz 1995),
but are more subject to predation than other animals.
in some cases, native ungulates may be managed to help restore
historic grazing regimes.
(Frost and Launchbaugh 2003, Tu et al. 2001, Coffey 2001)
Although cattle generally prefer to graze grasses and avoid weedy forbs, incentives and behavior
modification techniques can be used to encourage livestock to eat weeds that they would not normally eat.
Grazing behavior can vary widely among breed, age, sex, body condition, hunger, and previous experience
of individual animals (Frost and Launchbaugh 2003). Infestation density, growth stage, and availability of
other foods also influence an animal's grazing behavior (Olson 1999b). Research is ongoing to identify
predictable grazing patterns, modify foraging behaviors, and even breed inherent dietary preferences.
Multispecies grazing takes advantage of the inherent grazing preferences among different classes of
livestock (Walker 1994). Multispecies grazing is the use of two or more herbivores to graze a common
resource. The grazing species can be wild or domestic animals. They can graze an area simultaneously or at
different times (Coffey 2001).
Grazing livestock species with
different dietary preferences (i.e.,
cattle and sheep) applies equal
pressure to the grasses and forbs
in a community, thereby reducing
the competitive advantage of one
plant group over another.
Sheep and goats can improve
rangeland and reduce the risk of
cattle being poisoned by grazing
toxic plants.
Cattle may deter predation and
provide protection for sheep
because they are larger and more
aggressive.
Timinq
Livestock species may exhibit
aggressive behavior or interfere
with another livestock species.
Sheep, goats, and cattle require
different mineral supplements.
Sheep, goats, and cattle have
different fencing and herd
management requirements.
By introducing grazing animals into an area at the proper time, land managers can interrupt invasive plant
reproductive cycles and take advantage of differential vulnerability and palatability of target versus
nontarget plants.
Animals should be brought into an infested area at a time when they will be most likely to damage the
target invasive plant species without significantly impacting desirable Vegetation.
Grazing timed to remove developing flowers or seedheads can reduce seed production for that year
(Williams and Prather 2006, Olson et al. 1997, Thomsen et al. 1996). However, grazing weeds during seed
set may not be advisable because of risk of livestock spreading seeds.
Intensitv
Grazing intensity is typically described as "low," "moderate," or "high" and can be manipulated to control
the level of defoliation and impact produced by livestock. Grazing intensity levels are a factor of how many
(stocking rate), how long (duration), and how often (frequency) livestock animals are allowed to graze in
an area.
Light stocking rates can be used to take advantage of an animal's inherent dietary preferences in sparse
infestations of relatively palatable plants. Heavy stocking rates can be used to force more even use of
forage in dense infestations or less palatable plants (Frost and Launchbaugh 2003).
Grazing intensity should be closely monitored and the animals promptly removed when the proper amount
of defoliation or impact has been achieved. As a rule, livestock should not be allowed to graze more than
60% of the desirable plant foliage and consumption of target plants should significantly exceed
consumption of desirable plants (Olson 1999a).
The interval between grazing periods allows recovery of grazed plants. One-time defoliation, even at a
plant's most susceptible stage has a minimal impact on most weedy forbs. Therefore, repeated grazing
within one season for several years is often required to control some plants.
Monitorinq
A critical step in developing an effective and ecologically -sound grazing prescription is establishing criteria
by which the prescription's implementation and effectiveness will be measured. By collecting quantitative
data over time, one is better equipped to detect trends toward or away from the desired effects of grazing
treatments. Furthermore, monitoring during grazing treatments will help to determine whether grazing
treatments are applied at the appropriate season, duration, frequency, and intensity.
In general, monitoring activities should determine whether treatments are being applied as prescribed,
meeting invasive plant management objectives, and having desired effects on the plant community.
Invasive Plant Management Options
Prescribed grazing can be used to implement a number of invasive plant management options.
Prevention
With proper management, livestock can be
used to develop and maintain desirable
vegetation conditions and help prevent
invasive plants from establishing. Grazing at
the early stages of plant invasion can help
reduce colonization and slow the rate of
invasion.
Containment
Grazing applied at the appropriate growth
stage can prevent flower and seed
production, thereby containing plant
populations that spread by seed. Once a plant
community is dominated by an invasive plant,
realistic grazing goals may be to use the
invasive plant as forage while taking care to
prevent expansion of infestations.
Suppression
Moderate densities of invasive plants may be
suppressed through prescribed grazing. Selective
grazing applied over the long term can gradually
reduce the invasive plant's competitive ability within
the plant community.
Eradication
Eradicating invasive plants is rarely, if ever, a realistic
strategy when using livestock grazing alone.
• Treatments can be removed
at any time without leaving
residues or long-term effects.
• Treatments can be applied to
steep, rocky, and remote terrain.
• Grazing animals convert the
target species into a saleable
product such as meat or wool.
• Grazing can provide long-term
management while reducing the
use of herbicides.
Intecirated Methods
Grazing requires continual
monitoring and management to
achieve desired results and avoid
negative nontarget effects.
• Livestock animals may not be
compatible with some sites and may
conflict with land use.
• Appropriate animals may not be
available to target some invasive
plant species.
Prescribed grazing may be applied alone or combined with other invasive plant management methods.
When applied alone, the effects of prescribed grazing can be very slow to appear and often require repeated
treatments over a number of years to effectively suppress most target plant species. Integrating prescribed
grazing with other invasive plant management methods can mutually enhance each method and can
produce more rapid, long-term effects than the same methods used alone.
Prescribed Grazina and Phvsical Methods
Grazing can be used to clear vegetation and facilitate access to a site, or remove excess canopy vegetation
to aid in locating low -growing target species for treatment with physical methods.
Prescribed Grazina and Chemical Methods
Grazing may be applied either before or after herbicide treatments to enhance the effectiveness of either
treatment. On spotted knapweed- (Centaurea maculosa)-infested rangelands in western Montana, spring -
applied herbicide treatments enhanced sheep grazing by shifting knapweed populations from mature, less -
palatable plants to juvenile plants preferred by sheep (Sheley et al 2004). In North Dakota, moderate sheep
grazing followed by a fall -applied herbicide treatment resulted in more rapid and long-term leafy
spurge (Euphorbia esula) control than either method used alone (Lym et al 1997). Grazing leafy spurge
during spring and summer can reduce canopy and stimulate shoots to grow in the fall. A fall application of
an appropriate herbicide then acts on the rapidly developing regrowth.
Prescribed Grazina and Prescribed Burninq
Grazing can be used to manipulate fire intensity by deferring (to increase fuel load) or increasing
defoliation (to decrease fuel load) (DiTomaso and Johnson 2006). Fire can be used to stimulate regrowth
and increase palatability of some invasive plants. However, desirable plant populations may also be more
vulnerable to the negative effects of grazing following a burn event.
Prescribed Grazina and Restoratio n/Reveaetation
Livestock animals can be used to restore degraded lands by breaking up the soil surface and incorporating
seeds of desirable plants.
Prescribed Grazinq in Action
Domestic livestock grazing is a predominant land use in the western United States. Use of livestock for
invasive plant management is fairly well documented in this region (Olson and Lacey 1994, Walker et al.
1994, Olson et al. 1997a, Olson et al. 1997b, Olson and Wallander 1998, Thomsen et al. 1996). Examples
from the eastern United States are becoming more common as goats, sheep, and cattle gain popularity as an
"environmentally friendly" control method (Luginbuhl et al. 1996, Luginbuhl 2000, Escobar et al. 1998,
Hart 2000, Tesauro 2001).
Researchers and managers are finding creative ways to use goats, sheep, and cattle to control invasive
plants in a variety of environments. Although non -domesticated herbivores (i.e., grass
carp [Ctenopharyngodon idella]) have been introduced to control aquatic plants, current knowledge and
practice of prescribed grazing is generally limited to terrestrial habitats.
Logistical and monetary challenges come with adopting this method in Florida. Currently, there is not a
company in the state that is accepting new clients. The cost for goat rental is about $2,000.00 per acre (if
they were available). For the Storm Water Park (166 AC), it would be about $332,000.00 for each visit (4
may be required annually).
Harvesters
Harvesters are self-contained, modified barges with underwater cutting blades and conveyor belts that
remove material from the water column or surface and transport it to another location for disposal.
Considerations
Water uses and functions
o No water use restrictions
o May be the only option where herbicides are not effective or immediate removal is required
o Fast-moving water where herbicide concentrations cannot be maintained
o In areas where herbicides cannot be applied (drinking water intakes, brackish water)
o For plants that are not susceptible to herbicide control (lyngbya)
o Remove masses of plants or organics from bridge pilings and flood control structures
o Remove floating (especially drifting) masses of organic material (peat, muck)
Fish and wildlife
o Coordinate activities around nesting and foraging activities, especially birds and alligators
o Non -selective — removes all plant and animal species that cannot escape harvester path
o May select for invasive plants
o Removes slow -growing native plants mixed with invasive plants, like hydrilla
o Hydrilla recovers faster from harvesting than native plants and shades them out
o FL study: up to 32% removal of young -of -year sport fish per harvest in hydrilla
o Studies in other states show similar results of harvesting fish and invertebrates
Control feasibility
Harvest rate is generally slow
Removes 2-8 acres of aquatic plants per day — removal rate is influenced by:
Plant type
■ Submersed plants are more difficult to harvest than floating or emergent
■ Cutting blade and belt are well below water surface
■ Submersed plants are more difficult to see
■ Tall, emergent plants like cattail are difficult to collect on conveyor
■ Woody species like willow are difficult to cut
Weight — aquatic plants are mostly water
■ Hydrilla weighs approximately 20 tons per acre; water hyacinth ranges from
200-800 tons per acre
■ Organic content — floating islands can be composed of peat up to four feet thick
■ Invasive water hyacinth and hydrilla expand faster than harvesters can remove
them
■ Not effective in shallow water or in flooded timber reservoirs
■ Cannot reach plants where control may be important (shorelines, among trees or
snags)
■ Fragments of invasive plants like water hyacinth are left for immediate
recolonization
■ Can spread invasive plants like hydrilla or milfoil by creating numerous viable
fragments
■ Turbidity issues possible in shallow water or when hauling muck or peat across
lakes and rivers
Other considerations
o Expenses are generally high
o Acquisition cost of machinery
o High maintenance
o Operating costs
■ Invasive plants like hydrilla may require 2-3 cuts per year
■ Costs can double for each mile material is hauled within a water body
■ In -lake hauling costs can be reduced using higher speed transport barges
■ In -lake disposal sites close to harvest area reduce project cost
■ Sacrifice small area of lake bottom to stack material from large harvest area
■ Large in -lake disposal sites may provide wildlife habitat
■ May be public opposition (unsightly; odor from decaying plants)
■ Costs escalate if harvested material must be hauled to external disposal site
■ Loading and trucking expenses
■ Sealed dump trucks may be required for over -the -road hauling
■ Disposal fees may be required (rent private land, landfill)
■ Disposal site preparation and restoration costs may include:
leveling, water containment, spreading, drying, chipping or burning woody
material, temporary road preparation and dismantling, reseeding, pave
streets or driveways damaged from heavy equipment
o Few uses for harvested material
■ Aquatic plants are mostly water (90%+)
■ Harvesting and processing costs exceed market value of any product
■ Organic material from floating islands can augment poor soil or be used
as fill
o Cost-effective for small-scale projects, especially native plant removal
Examples of Feasible Control:
o Harvest lyngbya from Crystal River where fast -flowing springs and tidal action preclude herbicide
use
o Remove floating islands of herbaceous and woody vegetation and buoyant organic sediments up to
four feet thick on Lake Lafayette and Orange Lake
o Immediate removal of floating masses of plants from bridge pilings on the St Johns River
o Maintain established trail system through multiple native plant species on Lake Tsala Apopka,
where several different herbicides would be required to control different plant types.
Shore -based track hoes or draglines
Shore -based track hoes or draglines are machinery that lifts aquatic plants and associated organic material
directly from the water and piles it along shorelines or into dump trucks for off -site disposal.
Considerations
Water uses and functions
o No water use restrictions
o Usually for emergency removal of debris at bridges or flood control structures
o More reactive vs. preventive or proactive management
Fish and wildlife
o Few wildlife restrictions if conducting emergency removal from shore or structures
o Coordinate activities around nesting and foraging activities, especially birds and alligators
Control feasibility
o Harvest plant material accumulating in flood -control canals and structures or against bridges
o May need to remove material to disposal site
o If hoe or crane is on bridge, may need to alter or shut down traffic
o Harvest rate is generally slow
o Best suited for emergent and woody species and thick floating masses of organic material
o Harvest wind-blown floating tussocks, floating islands or debris from lake shorelines
o Need access to shoreline for removal equipment
o Harvesters or tugs may need push vegetation or organic material to track hoe or dragline
o May raise turbidity issues in shallow water
o Fragments or debris may drift downstream
Other considerations
o Expenses are generally high
o Acquisition cost and maintenance of machinery
o Operating costs — depends on plant type and amount of suspended organic composition
o Herbaceous vs. woody plants vs. trees
o No suspended organic material to peat up to four feet thick
o May need disposal site to:
■ Remove material from private property
■ Prevent material from washing back into water body
Examples of Feasible Control:
o Floating islands and tussocks that drifted out of Lake Hancock and clogged the Peace River flood
control structure were shredded to facilitate removal with a track hoe.
o Hurricane Wilma blew floating plants and ripped up cattail onto the rim canal on Lake
Okeechobee where they were removed via land -based track hoes.
Barge -Mounted Track Hoes or Draglines
Barge -Mounted Track Hoes or Draglines are similar to harvesters, except that material is lifted out of the
water by grappling devices or buckets rather than conveyor belt. Applications and considerations are
similar.
Considerations
o Generally more cost-effective at removing floating islands than herbaceous plants
o Pickup woody species or trees that could jam conveyor harvesters
o Not cost-effective for submersed plant removal
Examples of Feasible Control:
o Barge -mounted dragline and hoes removed about 35 acres of dense floating island material (peat
up to 4 feet thick, trees up to 10 inches in diameter and 50 feet tall) from boat ramps and
residential shorelines and docks on Lake Pierce generated by Hurricane Charlie in 2004.
Other Considerations
The City contacted several companies to provide estimates for 1) the removal of the overgrown vegetation
and 2) the maintenance using non -chemical methods. The companies have current contracts with other
agencies in Florida.
Texas Aquatics is a company that attended the FWC meeting in Okeechobee. They currently have a
contract in place with FWC for mechanical harvesting. The City Manager contacted them at that meeting
and they never responded. The City Manager contacted them once again and they came out and looked at
several areas. They could not provide service in the small ponds due to water levels. Additionally, they
advised that their process is not much different than mowing the vegetation under water and stated they will
be back in a few weeks, after they are done. Staff took them to the Elcam canal and they advised they
would provide pricing. However, after numerous attempts they never responded back.
The City's current contractor, Applied Aquatics provided an estimate for manual maintenance for the
Elcam canal, at an estimated annual cost of $400,000.00. This again, is only an estimate. Because the
quantities and frequency of treatments remain unknown at this time, exact man hours to provide this service
cannot be determined.
Arbor Tree and Landscape has a contract with The South Florida Water Management District and gave a
potential budget estimate to remove the overgrowth on the Elcam canal of $500,000.00. A quote for annual
maintenance was not provided, as the quantities and amount of service are not known.
Lake and Wetland Management provided a budget quote of $1, 250,000.00 to clear the Elcam canal, a
proposal for physical labor of $629,200 (based on $3,146.00 per day X 200 days), a proposal for canal
removal of $793,600.00 (based on $3,146.00 per day X 200 days), and a proposal for a small mechanical
weed remover for small ponds and ditches of $621,000.00 (based on $3,146.00 per day X 200 days). These
proposals do not include the disposal of the materials.
Hand -Pulling
Physical weed removal is part of an integrated pond -management plan, but physical removal has
limitations. It is best suited to very small ponds when there's not much time available to clean up a weed -
bound pond.
Hand -pulling requires digging out plants and their roots, or lifting or netting floating plants from the water
surface. Plant material is then deposited away from the shoreline. Hand -pulling is practical for controlling
small amounts of aquatic plants in easily accessible, shallow water. Otherwise the process may require the
assistance of trained SCUBA divers. The effectiveness of hand -pulling depends on sediment type, water
visibility and thoroughness of removal. A high degree of control, lasting more than one season, is possible
depending upon the species of plant and if complete removal can be achieved. In many cases, hand pulling
small amounts of plants from residential shorelines does not require a permit.
Physical aquatic weed removal can be short-lived, as most aquatic plants and algae are capable of
reproducing through fragmentation. The biggest concern with physical removal is that the pieces of
vegetation left behind provide a "jump start" for new growth. This is why state and federal fish and wildlife
agencies stress careful cleaning of boats, trailers, and live wells when boating in lakes that contain exotic or
invasive plant species.
Physical aquatic weed removal only removes the parts of the plant above the pond bottom and leaves the
roots intact. The results of physical removal are immediate, but usually very short-lived. This should be
kept in mind when budgeting for long-term solutions to aquatic weed growth.
Physical removal can be an effective tool in small ponds if time is a factor. Many times, a pond owner has a
special event planned where waiting 7-10 days for chemical control is not acceptable. In these small ponds,
algae or floating plants can be skimmed off of the surface for immediate results. However, this can be very
labor-intensive and disposal of the removed material is also a concern.
Diver -Assisted Dredging
A variation of hand -pulling is diver -assisted dredging: Divers working in deep water, hand -pull plants and
feed them into a flexible, four -inch hose. The hose is connected to a vacuum pump on a barge, boat or
dock, which draws up both water and plant material. Plants are screened and deposited on an upland site,
away from the water body. Diver -assisted dredging has been used only in the fast-moving waters of the
Wakulla River to remove hydrilla from small, high -use areas where mechanical harvesting or herbicide
applications were not practical.
Barriers
Fences, Booms, and Cables
Fences, booms, and cables have been employed for decades in Florida public waters to keep floating plant
masses out of particular areas. Historically, fences were erected along sections of the St. Johns River to
prevent water hyacinths from blocking the navigation channel, and booms were stretched across canals to
keep water hyacinths from spilling into (or out of) adjacent lakes.
More recently, pilings and cables have been installed at the outfalls of lakes or in front of flood control
structures to keep floating rafts of plants (also called tussocks or floating islands) from clogging these water
conveyances. State or federal permits may be required prior to installing any device in public or navigable
waters.
Benthic
Benthic barriers consist of materials such as sand and gravel, burlap, plastic, fiberglass screens, nylon, and
other synthetic substances that cover rooted plants and prevent them from growing. Benthic barriers
typically kill the covered plants in one to two months and prevent new plants from growing. Benthic
barriers are labor intensive to install and maintain and are therefore generally restricted to small locations,
such as ornamental ponds, swimming areas, and around boat docks. Benthic barriers are not selective; they
control all plants and other living organisms that are covered. Plants will eventually regrow if sediments
accumulate on top of the material.
Silt Curtains
Other types of barriers such as silt curtains can assist in aquatic plant control efforts. Silt curtains are
suspended vertically from the water surface to the sediment. They are used to augment herbicide treatments
by prolonging herbicide contact with plants behind the curtains in isolated coves or along shores of large
open systems where wave action can quickly dissipate herbicides. They also are used to deflect water
currents away from herbicide -treated areas in slow flowing rivers, streams, or spring runs to minimize
dilution. As with benthic barriers, silt barriers are expensive to install and maintain, so their application is
limited to small areas where other options are less practical. State or local permits may be required to install
benthic barriers.
Cutting / Shearing
Cutting or shearing requires the use of a variety of tools. Machetes simply chop plants. Tethered rakes or
blades are thrown into the water and retrieved by hand. Heavy metal weights, chains and even bed springs
can be towed through weed beds to cut or pull plants from the bottom. Hand -cutting can minimize
environmental disruption if done with care, but rapid regrowth is possible if the roots are not removed.
Cutting is time-consuming, labor-intensive, and the effects generally last less than one growing season.
Tossing a tethered blade into the water to shear plants and then raking debris from the water can be cost-
effective for clearing small shoreline areas. Dragging heavy weights along the bottom is not practical for
lakes and rivers, but may be an option for controlling aquatic plants in ditches and canals.
However, it's likely this will stimulate more root growth. Most submerged aquatic weeds, like spatterdock
or water lilies, have deep roots. A blade won't pull up those roots. These roots strengthen helping the
aquatic weed to grow back strong like "pruning". In the case of parotts-feather, it means fragments with
roots are spread throughout the pond, resulting in more weeds than those that were there in the beginning.
Water Level Manipulation
Prior to urbanization and flood control efforts, Florida's shallow lakes underwent periodic drying and
flooding. Nowadays, water levels in most of Florida's "natural" lakes are regulated for flood control, crop
irrigation or drinking water by structures such as dams, weirs, and gates, or conveyances such as outfall
ditches and canals to other waters. These water level manipulations provide for year-round recreational and
other water uses, but also allow dense plant growth and muck accumulation if the waters never dry up or
flood. Managers seek to mimic nature through a variety of water level manipulation techniques.
Drawdown
Drawdown, also called drydown or dewatering, refers to the lowering of water levels. It has been used for
centuries to expose to air (oxidize) and dry excess sediment or muck, alter fish populations, and control
aquatic weeds. This technique requires a dam or other structure to lower water levels. The process may be
restricted by public needs for water, water rights, or the lack of a predictable source of water for refilling.
In Florida, drawdowns are most effective for controlling floating, emergent, and submersed plant species in
the winter to take advantage of drier weather, freezes, and prescribed fire to further suppress target plants.
Fluctuating Water Levels
Because it is nearly impossible to completely drain most Florida lakes, resource managers also seek to alter
water levels to augment aquatic plant control efforts. Lowering water levels by several inches to several
feet increases water holding capacity so that unanticipated rainfall does not flush herbicide -treated waters
from the system. It also reduces the lake volume, thereby reducing the amount of herbicides needed. This
translates to lower management costs. For example: A six-foot reduction in water level on 19,000-acre
Lake Toho (Osceola County) greatly reduced herbicide amounts used for hydrilla control and saved
approximately six million dollars in one year.
Flooding
After an herbicide application to control submersed invasive species like hydrilla, managers sometimes
work to increase water levels by several feet to reduce light penetration through the water. This further
stresses target plants and extends the duration of control. Flooding, an extreme example of water level
fluctuation, can be used in lakes to strand invasive floating plants like water lettuce. Flooding can be used
especially when favorable wind conditions push target plants to secluded shorelines. Water levels are then
quickly reduced to leave stranded plants in dry upland areas where they do not survive. This strategy is
used approximately every three years on Rodman Reservoir (Putnam/Marion Counties).
Other water level manipulations include reflooding dried marshes in Lake Okeechobee to suppress the
regrowth of torpedograss controlled with herbicides or prescribed fire; and increasing water levels to
approximately four feet for extended periods to reduce dense stands of cattail.
Prescribed Fire
Fire is a natural process that commonly occurs when Florida's shallow lakes and marshes dry out. For
centuries, periodic burning sparked by lightning or extremely dry weather has controlled dense plant
growth in Florida lakes and marshes. Managers use prescribed or planned fire to intentionally burn the
thick build-up of plants and organic debris called thatch.
Thatch can accumulate quickly in stabilized water bodies when they dry out. Fire also stimulates new
growth of some invasive plants such as torpedograss, making them more susceptible to herbicide
treatments. Prescribed fire requires careful planning, permits and consideration of the impacts to air quality,
human health and safety, protection of structures, and motorist visibility.
Sediment Removal
Scraping
In some cases during extreme droughts or prescribed drydowns, accumulated vegetation and sediment
(muck) may be removed from a lake or reservoir. In Lake Jackson (Leon County), scraping machines and
dump trucks removed years of accumulated sediment from the exposed lake bottom after a natural sink
hole opened and drained much of the water. Another muck removal project took place on Lake Toho.
Dredging
In other cases, vegetation and sediments may be removed by dredging. In this case, water remains in the
system and sediment is removed using floating dredging machines and pumps (see Lake Trafford (Collier
County)). In other cases, floating masses of aquatic vegetation and sediments are shredded to facilitate
dredging (see Lake Panasoffkee (Sumter County)).
Sediment removal is expensive and causes significant environmental impacts. Therefore, a considerable
amount of planning and permitting is involved to identify priority control areas, minimize impacts to water
quality and locate suitable disposal sites. Most sediment removal projects are conducted to alleviate
problems associated with the accumulation of organic material, and aquatic plant control is a side benefit
rather than a management goal. No matter how thorough, sediment removal leaves seeds and other
reproductive material behind and aquatic plants usually regrow fairly quickly in Florida's shallow waters.
Light Attenuation (Dves)
Light attenuation or reduction limits plant growth by reducing light penetration into the water and
inhibiting photosynthesis. Sunlight is obstructed by special non -toxic (usually blue) dyes. Light attenuation
mimics the natural effects of tannins or turbidity in the water and is most effective for controlling
submersed rooted plants or algae. The concentration of dyes must be sufficiently maintained in the water,
so this method of control is limited to small, shallow ponds.
Nutrient Manipulation (Fertilization]
Plant growth can be affected if at least one essential nutrient is limited. Nitrogen and phosphorus are the
most common nutrients influencing plant growth in Florida lakes.
Nutrient manipulation involves the application of aluminum, iron salts or calcium compounds (lime) to
remove phosphorus from the water and to inactivate phosphorus in the sediment. Most rooted plants take
up nutrients from sediments, not water. Aluminum sulfate (alum) is most commonly used. Removing or
inactivating phosphorus can effectively reduce algal blooms, but the growth of most rooted plants is limited
by nitrogen and there are no compounds readily available that inactivate nitrogen. Nutrient manipulation is
best suited for water quality improvement and algae control. However, reducing nutrients and algae in the
water may encourage more growth of aquatic weeds due to improved water clarity and light penetration,
allowing weeds to grow in deeper areas.
Aeration
Aeration increases dissolved oxygen in the water, usually causing blue-green algae to be replaced by green
algae. Water can be aerated using fountains at the water surface to increase circulation or by compressed air
bubblers at the bottom that release oxygen into the water. Some researchers suggest that aerating water
causes the deposit of iron oxide compounds on submersed plants which interferes with photosynthesis.
Others suggest that aeration promotes the growth of filamentous algae that interferes with photosynthesis in
submersed plants. Whatever the cause, aeration can be used for some degree of aquatic plant control in
small systems.
Input provided by other Florida Communities:
In researching alternatives, the City Manager reached out to several communities that have either banned or
regulated the use of Glyphosate. See chart below.
Municipalities Ban or Reduced Use Alternatives
Stuart FI. Trade Name
Chemical Name
Aquatic Use Label
Tribune
Diquat Dibromide
Yes*
Finale
Glufosinate-Ammonium
No
Sure Guard
Flumioxazin
No
Mirimichi Green
Ammonium Nonanoate
No
Green Gobbler
30% Vinegar
No (per Manufacturer)
Fort Myers Beach There is no stated replacement although we have had good results with diluted 30% vinegar solutions.
Brgds. R.
Miami
Mirimichi Green Ammonium Nonanoate No
Reward Diquat dibromide Yes
We have not found an alternative for this other than hand pulling or a excavation machine. To
Satellite Beach
replace the Round Up, we found an organic alternative, called Miramichi and we also have
decided to quit spraying in certain areas, such as around fence lines.
Evanston III.
Tryclopyr Tryclopyr Yes
T Zone 2 4D Yes*
Relegate Clethodim No
Phydora Dicamba No
Snapshot Trifluralin No
Garlon 24D Yes*
Vinegar 30% No
Hallendale Beach
Finale Glufosinate-Ammonium No
They do not do aquatic herbicide.
* Special Instructions for aquatic use
Estimates Obtained:
The City contacted several companies to provide estimates for the removal of the overgrown vegetation and
a cost estimate for the maintenance using non chemical methods. The companies have current contracts
with other agencies in Florida.
Texas Aquatics is a company that attended the FWC meeting in Okeechobee. They currently have a
contract in place with FWC for mechanical harvesting. The City Manager contacted them at that meeting
and they never responded. The City Manager contacted them once again and they came out and looked at
several areas. They could not provide service in the small ponds due to water levels. Additionally, they
advised that their process is not much different than mowing the vegetation under water and stated they will
be back in a few weeks, after they are done. Staff took them to the Elcam canal and they advised they
would provide pricing. However, after numerous attempts they never responded back.
The City's current contractor, Applied Aquatics provided an estimate for manual maintenance for a section
of the Elcam canal, at an estimated annual cost of $400,000.00, This again, is only an estimate. Because
the quantities and frequency of treatments remain unknown at this time, exact man hours to provide this
service cannot be determined.
Arbor Tree and Landscape has a contract with The South Florida Water Management District and gave a
potential budget estimate to remove the overgrowth on a section of the Elcam canal of $500,000.00. A
quote for annual maintenance was not provided, as the quantities and amount of service are not known.
Lake and Wetland Management provided a budget quote of $1, 250,000.00 to clear the Elcam canal, a
proposal for physical labor of $629,200 (based on $3,146.00 per day X 200 days), a proposal for canal
removal of $793,600.00 (based on $3,146.00 per day X 200 days), and a proposal for a small mechanical
weed remover for small ponds and ditches of $621,000.00 (based on $3,146.00 per day X 200 days). These
proposals do not include the disposal of the materials.
Staff's Summary and Reauest for Direction from Council:
As these alternatives are considered, Staff proposes to look at several methods in managing both the aquatic
and terrestrial vegetation within the City. First, the City must regain control of the overgrowth that is
reducing its ability to maintain its canals. Once this is completed, the City can use mechanical methods on
the banks to keep the invasive plants under some control. Some chemicals on water -based plants must be
used, as the research shows that mechanical and hand removal will not be sufficient to maintain this at
acceptable levels. We have the option where feasible, to use beneficial aquatic plants for water quality and
soil erosion.
The small ponds in the neighborhood parks are in desperate need of dredging. This in itself will help reduce
the vegetation and improve water quality. After this is performed, the City may be able to look at what
grows back and then determine the methods that should be used for control. This process will take several
years due to budget constraints.
There has finally been a release of a Thrip for Pepper trees that is showing some promise and once
available, the City can look at having it released. There is an Air Potato bug that the City will look at
acquiring and using in the Stormwater Park to try and stem the advancement of this plant.
Several areas in the waterways have been planted by homeowners with both native and non-native invasive
species. This will need to be addressed throughout this process and continue with code enforcement to help
prevent this in the future.
Some of the challenges are the vacant lots along the waterways. As the canal rights of ways are established,
the City will need to treat the encroachment of nuisance vegetation in the same manner as it is done on
other vacant lots. The City can provide the owner with an opportunity to remove the encroachment and if
they do not comply, the City can have its contractor remove it and bill the property owner for the work and
the administrative fees, as ordered by the Special Magistrate.
As the City evaluates its management processes, it needs to look at not only cost considerations, but also
effectiveness. The products that have been suggested as natural, which are labeled for vegetation are not
however labeled for aquatic use. So, the City's options are limited to reduction of treatments combined
with mechanical and or manual removal. Depending on the amount of treatment, this cost for the canals
could be $400,000.00 per year. But again, without knowing the recidivism of the vegetation, this could be
more or less. If the City takes a measured approach and concentrates on some sections of the canals and
observes the amount of required treatments moving forward, then the most acceptable methods based on
that information can be determined.
The City should develop a capital improvement plan that will address the sediment in the canals, the
encroachment of vegetation and aquatic plantings to improve water quality, aquatic habitat and shoreline
stabilization.
The plan moving forward has several options that would need to be discussed in greater depth to determine
the process moving forward.
Option 1. Keep the current program in place without any changes. The following costs are
associated with this are:
• Contractor spraying $ 60,000.00
• Staff and equipment (all divisions) $1,860,000.00
• Totals $1,920,000.00
Option 2. Use alternative spray chemicals with reduced use of Glyphosate, but keep drainage
systems in current condition and functioning at current levels.
• Contractor spraying $ 300,000.00
• Staff and equipment (all divisions) $1,860,000.00
• Totals $2,160,000.00
Option 3. Use alternative treatments and organic treatments where applicable and no Glyphosate
use.
• Contractor spraying $1,300,000.00
• Staff and equipment (all divisions) $1,860,000.00
• Totals $3,160,000.00
Option 4. Limited chemicals with manual and mechanical removal.
• Contractor man power and equipment. $2,073,000.00
• Staff and equipment (all divisions) $1.860.000.00
• Totals $3,933,800.00
Option 5. The use of limited chemicals, mechanical removal, and capital restoration and plantings.
• Contractor maintenance $ 300,000.00
• Staff and equipment (all divisions) $1,860,000.00
• Capital restoration projects $ 500.000.00
• Totals $2,660,000.00
The information contained in this report was a collaborative effort with the University of Florida/IFAS and
the Florida Fish and Wildlife Conservation Commission and the City of Boca Raton.