Aquatic Pesticide Monitoring Program 

Review of Alternative Aquatic Pest 

Control Methods For California Waters 

Ben K. Greenfield 

Nicole David 

Jennifer Hunt 

Marion Wittmann 

Geoffrey Siemering 

San Francisco Estuary Institute 

7770 Pardee Lane, 2nd Floor 

Oakland, CA 94621 

April 2004 
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Table of Contents: 

Disclaimer and Acknowledgements ..................................................................................iii 

Introduction......................................................................................................................... 2 

Review Design.................................................................................................................... 4 

Literature Review............................................................................................................ 5 

Practitioner Survey.......................................................................................................... 5 

Biological Control Methods................................................................................................ 6 

Pros and Cons of Biocontrol........................................................................................... 6 

Triploid Grass Carp......................................................................................................... 7 

Other Herbivorous Fishes ............................................................................................. 11 

Fish Biomanipulation.................................................................................................... 11 

Terrestrial Herbivorous Mammals................................................................................ 13 

Gastropod Mollusks...................................................................................................... 13 

Insects ........................................................................................................................... 14 

Predatory Animals For Mosquito Control .................................................................... 16 

Commercially Available Biocontrol Agents................................................................. 17 

Plant Pathogens Currently In Development.................................................................. 18 

Pathogens For Mosquito Control.................................................................................. 20 

Cyanobacteria Control Agents Currently in Development........................................... 20 

Organic Material Amendment ...................................................................................... 21 

Acetic Acid ................................................................................................................... 22 

Management Considerations For Organic Material Amendment................................. 23 

Plant Competition ......................................................................................................... 24 

Physical and Mechanical Control Methods ...................................................................... 25 

Mechanical Harvesting ................................................................................................. 25 

Environmental Effects of Mechanical Harvesting........................................................ 29 

Mechanical Cutting....................................................................................................... 31 

Rotovation, Rototilling and Hydroraking ..................................................................... 34 

Weed Rollers and Sweepers.......................................................................................... 36 

Diver-operated Suction Dredging................................................................................. 37 

Sediment Removal........................................................................................................ 37 

Shading and Piping ....................................................................................................... 37 

Bottom Barriers............................................................................................................. 38 

Manual Removal........................................................................................................... 40 

Water Level Manipulation ............................................................................................ 42 

Channel Clearing or Excavation ................................................................................... 43 

Exposure of Plants to Extreme Environmental Conditions (Heat, Steam, Flame, Cold, 

or Electricity) ................................................................................................................ 45 

Aeration, Oxygenation, and Water Circulation ............................................................ 45 

Nutrient Removal.......................................................................................................... 48 

Non-conventional Chemical Controls............................................................................... 49 

Calcium-based Products................................................................................................ 50 

Aluminum based products ............................................................................................ 51 

Nitrate ........................................................................................................................... 52 
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Aquashade..................................................................................................................... 52 

Salt (Sodium Chloride) ................................................................................................. 53 

NPDES Permitting Status of Non-Conventional Chemicals ........................................ 53 

Preventive Measures ......................................................................................................... 54 

Early Detection ............................................................................................................. 54 

Quarantine and Regulation ........................................................................................... 55 

Education and Outreach................................................................................................ 56 

Riparian Buffer Strips................................................................................................... 56 

Retention Pond or Wetland Construction ..................................................................... 57 

Watershed Best Management Practices ........................................................................ 57 

Relative Reliance on Conventional Pesticides vs. Alternative Methods .......................... 58 

General Permitting Requirements For Non-Chemical Methods....................................... 60 

General Discussion ........................................................................................................... 61 

References......................................................................................................................... 62 

Appendix A: Contractors/ Retailers That Specialize in Non-Chemical Control Methods79 

Contractors who conduct Non-Pesticide Control Methods .......................................... 79 

Companies that Manufacture and Sell Aquatic Plant Harvesters or Other NonChemical Devices ......................................................................................................... 80 

Appendix B: Practitioners Interviewed For Review......................................................... 82 

California Practitioners ................................................................................................. 82 

Out of State Practitioners.............................................................................................. 88 

Appendix C: Feasibility Screening For Different Weed Control Methods ...................... 93 

Appendix D: Peer Review .............................................................................................. 102 
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DISCLAIMER AND ACKNOWLEDGEMENTS 

This report is the result of feedback by some members of the Aquatic Pesticide 

Monitoring Program Steering Committee that there is a need for thorough documentation 

on alternative aquatic pest control methods for California waters. This work is intended 

as an educational tool, including detailed discussion of alternative methods. This review 

does not evaluate conventional chemical pesticides; therefore, it should not be considered 

a guideline on all available aquatic pest control methods. No policy or regulation is 

expressed or intended by this report. 

We thank the APMP Steering Committee and Interested Parties for providing 

feedback and direction on this literature review. Thanks are also due to all the aquatic 

plant managers, scientists, regulators, and NGOs who agreed to be interviewed and 

provide literature and unpublished reports for this review. Any errors or omissions in 

presenting alternative pest control efforts are the responsibility of the authors, rather than 

those interviewed. David Spencer, George Forni, Lars Anderson, and Robert Leavitt 

provided constructive review comments on portions of this review, Joe DiTomaso and 

John Madsen constructively reviewed the entire document, and Roger Mann assembled 

some of that information in the Feasibility Screening (Appendix C). Amy Franz and Seth 

Shonkoff assisted with document review and formatting. The California State Water 

Resources Control Board is acknowledged for funding this review. 
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INTRODUCTION 

Aquatic plant and algae infestations can reduce the utility of water bodies for 

irrigation, aquaculture, potable water, navigation, and recreation, as well as obstruct 

drainage canals, which are needed for flood control prevention. Millions of dollars are 

spent annually to control aquatic weeds and algae (Joyce 1992), and California agencies 

invest heavily in programs to control nuisance aquatic plants (e.g., CDBW 2001; CDFA 

2003a). Over the next several decades, with increasing human population growth, 

demand for food and water will increase, exacerbating the need for efficient delivery of 

usable water in California and worldwide (Van Vierssen et al. 2001). 

The purpose of this review is to evaluate aquatic pest control methods that may 

serve as alternatives to registered chemical pesticides (Table 1). These alternatives 

include biological, mechanical, and physical control methods, as well as preventive 

measures. The review also discusses chemicals not registered as pesticides, including 

phosphorus-binding agents, acetic acid, and Aquashade. 

Biological methods include the introduction of insect species and sterile grass 

carp, as well as microbial biocontrol agents, enzymes, and the addition of organic 

material. Mechanical control methods include harvesting, cutting, shredding, pulling, 

rolling, rotovation, diver dredging, the placement of barriers to inhibit growth, and 

excavation. Physical control methods include shading, aeration, and water level 

drawdown. Manual cutting, pulling, and rolling are geared towards small-scale projects, 

obstructed areas, or individual waterfronts. Harvesting, rotovation, excavation, and 

dewatering are used in larger scale aquatic weed removal (Table 1). 

This document was written to discuss plant management methods that may be 

usable in California waters. Wherever possible, local case studies are described, and local 

environmental conditions and regulations are referred to. For readers desiring further 

information, several excellent reviews of aquatic plant control methods are readily 

available on the World Wide Web. Madsen (2002) provides a general review. Gibbons et 

al. (1999) provides recommendations for implementation of aquatic plant management 

plans. Systma and Parker (1999) review methods that are appropriate for irrigation 
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canals. The identification of aquatic weeds and other information on their biology are 

described in DiTomaso and Healy (2003). 

Table 1. Methods available for control of aquatic pests in California waters. 

Physical and Mechanical Control Methods Biological Control Methods

Mechanical Harvesting Triploid Grass Carp 

Mechanical Cutting Other Herbivorous Fishes 

Rotovation and Rototilling Fish Biomanipulation 

Hydroraking Terrestrial Herbivorous Mammals 

Weed Rollers Gastropod Mollusks 

Lake Sweepers Insects 

Diver-operated Suction Dredging Non-Insect Crustaceans (for mosquito control) 

Sediment Removal Predatory fishes (for mosquito control) 

Shading Commercially Available Biocontrol Agents 

Piping Microbial Pathogens (e.g., cyanophages) 

Bottom Barriers Fungal Pathogens 

Manual Removal Organic Material Amendment 

Water Level Manipulation Acetic Acid 

Channel Clearing Plant Competition 

Mechanical Excavation 

Exposure to Extreme Environmental Conditions Preventive Measures

Aeration, Oxygenation, and Water Circulation Early Detection 

Nutrient Removal Quarantine 

 Regulation 

Non-conventional Chemical Controls Education and Outreach 

Calcium based Products Riparian Buffer Strips 

Aluminum based products Retention Pond or Wetland Construction 

Nitrate Watershed Best Management Practices 

Aquashade 

Salt (Sodium Chloride) 

Aquatic plant control typically involves a balance of multiple management 

objectives. Different water body users may have varying definitions of how much 

submerged aquatic vegetation is acceptable (Van Nes et al. 1999). This can be 

particularly important because some management objectives can be incompatible. For 

example, reducing macrophyte biomass can result in increased algal blooms, and vice 

versa (Scheffer et al. 1993; Scheffer, 1999). Success of many control methods could be 

improved by the timing of application to the nuisance species. For example, water 

hyacinth control agents should be applied when the plant carbohydrate stores are at their 

lowest which generally occurs in the spring. Eradication when plants are young and 

shoots and leaves are small may also increase rates of success (Madsen et. al 1993). 

This review synthesizes past and present knowledge of alternative management 

options, providing a wide range of potential tools for controlling aquatic plants and algae. 
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Nevertheless, each combination of plant species, water body, and stakeholder needs will 

respond best to a particular set of management options. Often times, significant progress 

can be achieved with alternative techniques on the control of relatively small infestations. 

However, large infestations may be most effectively treated with conventional pesticides, 

either alone or in combination with alternative plant control methods (Madsen 2002). It is 

important to not limit the available options in vegetation management and to choose 

carefully which ones are best applied for certain scenarios, considering the managed 

species, ecological system, natural resource values, and stakeholder priorities. 

To determine the best management options, aquatic resource managers are 

encouraged to develop aquatic plant management plans that best address all user goals 

(Gibbons et al. 1999). If a practitioner wishes to decide among a specific suite of 

management options, they may want to formally compare their feasibility and cost 

effectiveness, using the Aquatic Plant Management Economic Methodology prepared as 

part of this project (Mann 2003). 

Some of the methods described in this review are also used to control mosquito 

larvae in California waters. Water level manipulation has a long use history in mosquito 

control, as larva production is elevated in stagnant standing waters. Mechanical removal 

of aquatic or wetland vegetation could reduce larval production in some cases. 

Additionally, biological control is commonly used to control mosquito production; 

mosquitofish (Gambusia affinis) and other animal species may be introduced to water 

bodies, where they prey on larval mosquitoes. 

REVIEW DESIGN 

An evaluation of plant control methods for potential use in California should 

include all methods and technologies available throughout the United States. This study 

includes a detailed evaluation of methods documented in scientific journal literature, 

agency technical reports and grey literature. Additionally, telephone or in-person 

interviews were conducted with 77 practitioners in California and other states to point out 

methods currently successfully applied in specific management circumstances. 
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Literature Review 

An extensive review of recent literature and survey papers was conducted. This 

included keyword searches using selected library search engines (e.g., the Web of 

Science, Biosis) and review of relevant articles in the past several years of relevant 

journals. For example, The Journal of Aquatic Plant Management 

(http://www.apms.org/japm/japmindex.htm) was reviewed since 1990, and Lake and 

Reservoir Management since 1996. The World Wide Web was also surveyed for gray 

literature using keyword searches on web search engines. An excellent source of gray 

literature regarding plant management is the Aquatic Plant Information Retrieval Service 

(APIRS) at the University of Florida (http://plants.ifas.ufl.edu/search80/NetAns2/).

Additionally, papers available from the U.S. Army Corps of Engineers Waterways 

Experiment Station Digital Archives were downloaded and reviewed. Finally, several 

frequently published research scientists in the field were contacted with reprint requests. 

Of the published papers, grey literature, and web documents evaluated, 177 were 

included in this report and cited in the references section. 

Practitioner Survey 

To augment the findings of the literature review with late breaking information 

from the field, practitioners were surveyed within California and other states. 

Practitioners were asked whether they knew of any novel techniques for control of 

aquatic pests that would serve as alternatives to application of chemical pesticides in 

specific management circumstances. Interviews generally ranged in length from 15 to 60 

minutes, depending on the time constraints of the interviewee and the information they 

had to share. 

Appropriate practitioners and experts for interviews were identified using 

publications of articles regarding non-chemical plant control methods, relevant reports 

and information on the World Wide Web, attendance at the Western Aquatic Plant 

Management Society conference, listings on the APMS and NALMS websites and 

recommendations through already established contacts. Contact information of all 

practitioners interviewed is available in Appendix B.
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BIOLOGICAL CONTROL METHODS 

Biological control involves using plant, animal, or fungal species or components 

to reduce the survival, growth, or reproduction of the nuisance species. This includes use 

of herbivores, such as grass carp or insects that consume parts or all of the nuisance plant 

species. Bacterial and fungal pathogens are also used. These cause disease to the nuisance 

plant species, thereby reducing survival and recruitment. Additionally, biological 

materials, such as bacteria, enzymes, barley straw, organic matter amendments, may be 

added to the system to reduce growth of nuisance plants or algae, without preying on 

them or causing disease. The proposed mechanisms for non-predatory biocontrol 

methods include competition for resources, and production of natural substances that 

inhibit the growth of the nuisance species. The development of biocontrol agents has 

been limited due to production difficulties, unresolved regulatory questions, virulence 

issues and lack of capital investment (Watson 2003). 

Biological control is often more successful when multiple methods are integrated. 

Plants weakened by insect damage or sublethal doses of chemicals are often more 

susceptible to pathogens. In water hyacinth management, for example, multiple insect 

species, insects combined with grass carp, or pathogens combined with chemical 

treatment are often more effective than individual treatment methods alone (Gopal 1987). 

Pros and Cons of Biocontrol 

Biocontrol for reduction of nuisance plants in aquatic systems has both positive 

and negative attributes (Charudattan et al. 2002). A positive aspect of biocontrol is that 

control agents are often host specific, so effects to non-target species may be reduced. 

Control agents can also reproduce in response to increases in nuisance species density 

often without reapplication of the agent. Development and registration (where necessary) 

of biocontrol agents is generally less expensive than chemical agents. Additionally, the 

ecosystem impacts under biocontrol can be more gradual, thereby allowing the system to 

adjust to loss of a species. 

However, biocontrol can have many potential disadvantages. An important risk is 

involved when new species are introduced as biocontrol agents. To be considered 

successful, these species are expected to persist indefinitely in the environment where 
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they are used, and may spread to new locations. Therefore, if there are any adverse 

effects resulting from the biocontrol agent, these effects may be difficult or impossible to 

control. Adverse effects of biocontrol agents could include loss of habitat for some fauna, 

competition with native species, and the production of toxic metabolites that are released 

to the environment. Other drawbacks include unpredictable success and rates of control 

that are slower than with chemical methods. Resistance in host species is unlikely to 

develop but can occur. Finally, agents that work in one area may not be suitable in all 

ecosystems. Climate, interference from herbicidal application, hydrological conditions, 

and eutrophication of the system can influence the effectiveness of biocontrol agents (Hill 

and Olckers 2001). The growth of nuisance weeds can be suppressed with the use of 

biocontrol agents, but not fully eliminated. 

Triploid Grass Carp 

The grass carp, also known as the white amur (Ctenopharyngodon idella), feeds 

on aquatic plants and can therefore be used as a biological tool to control nuisance 

aquatic plant growth. To reduce the potential for unintended consequences, grass carp 

must be sterilized for use in waters of the United States. Once grass carp are stocked in a 

water body, it may take several years for them to control the plant growth and decrease 

weeds to about 20% of the earlier plant cover (Washington State Department of Ecology 

2001). If practitioners stock enough fish to achieve control within the first few years, this 

can eventually result in detrimental effects to non-target plants, as the fish increase in size 

(e.g., Colle and Shireman 1994). If possible, it would be more cost-effective to stock a 

smaller number of fish, and wait for them to grow sufficient size to control the plant 

problem (Stewart and Boyd 1999). 

A wide range of field applications and scientific studies has demonstrated that 

grass carp can effectively reduce growth and biomass of undesirable vegetation (e.g., 

Leslie et al. 1994; Pauley et al. 1994; Santha et al. 1994; Van Vierren et al. 2001). 

However, success with grass carp may vary from site to site. Sometimes identical 

stocking rates result in no control, adequate control, or even complete elimination of all 

underwater plants. Therefore, before introducing grass carp to a water body, it must be 

determined whether complete elimination of all submerged species could be tolerated. 
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Many researchers and aquatic plant managers think that grass carp should only be 

stocked when complete elimination of all submersed plant species could be tolerated. 

As with any large-scale ecosystem manipulation, grass carp introduction may 

cause significant environmental impacts to a water body. Elimination of submerged 

plants by grass carp foraging could result in increased turbidity, water column nutrients, 

and phytoplankton production (Scheffer et al. 1993; Colle and Shireman 1994; Scheffer 

1999). If all aquatic vegetation is removed, waterfowl, amphibians and aquatic mammals 

may also be adversely impacted (Brakhage 1994). In light of the fact that grass carp, once 

introduced, are extremely difficult to remove from a water body (e.g., Colle and 

Shireman 1994), caution should be exercised when considering new waters for grass carp 

introduction. 

Case study results vary widely in overall impacts of grass carp introduction to 

native plant and animal communities. Overstocking can result in disturbance to the 

existing fish community, resulting from vegetation habitat removal. In two Florida lakes 

heavily stocked with grass carp, all submerged vegetation was wiped out, resulting in 

impaired water quality and declines in sensitive native fish species (e.g., Colle and 

Shireman 1994). In contrast, when grass carp were carefully stocked in eight Oregon and 

Washington lakes, dissolved oxygen improved and other fish populations were not 

affected (Pauley et al. 1994). By reducing dense monotypic vegetation, and increasing 

underwater structural diversity, grass carp introduction may even increase abundance of 

other fish species (Killgore and Kirk 1998; Killgore et al. 1998). 

California Department of Fish and Game has implemented a number of 

restrictions to reduce the probability of negative consequences of grass carp use. First of 

all, grass carp may only be used in water bodies that are isolated from the 100-year 

floodplain of major California rivers (Marty Muschinske, pers. comm.). Due to the risk of 

adverse impacts on adjacent water bodies, stocked water bodies should be isolated or 

have screened inlets and outlets (Washington State Department of Ecology 2001). 

Screens to inlets or outlets are generally only approved by CDFG where they do not 

interfere with anadromous fishes, e.g. steelhead or salmon runs. Additionally, grass carp 

must be sterilized, a process achieved by causing fertilized eggs to retain three sets of 
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chromosomes (triploidy). The risk of inadvertent release of fertile grass carp (e.g., Webb 

et al. 1994) is reduced by testing the blood of juvenile fish to confirm triploidy. 

In California waters, stocking costs include the purchase price of the fish 

(generally about $8-15/fish), purchase cost for the permit ($100 application fee), a onetime stocking fee of 15$/fish paid to CDFG, and an annual regulatory fee of $7.50/fish 

also paid to CDFG. Inquiries can be submitted to the local region office of CDFG or to 

Marty Muschinske, of the Eastern Sierra/Inland Desert region, who currently has the 

most experience with the program (Marty Muschinske, pers. comm.). Applications are 

evaluated by the local region office. Stocking rates for Washington lakes generally range 

from 9 to 25 eight to eleven inch fish per vegetated acre. This number will depend on the 

amount and types of plants as well as water temperatures (Washington State Department 

of Ecology 2001). One-year-old fish (less than 225 grams body weight) have much lower 

plant feeding rates than larger fish (Pine et al. 1990), so if small fish are stocked, foraging 

rates may increase considerably with fish size. 

For any given water body, it can be difficult to determine the optimal number of 

grass carp to stock. In the 1980s and 1990s, stocking rates varied widely among U.S. 

water bodies (Stewart and Boyd 1999). The optimal stocking rate is generally higher in 

Oregon and Washington than in southeastern United States (Pauley et al. 1994), 

suggesting that cooler water bodies in northern California would require higher stocking 

rates than warmer southern California waters. Currently, a number of California 

practitioners often report simply stocking a fixed number of fish per year, based on the 

general observation of successful weed control (Paul Saunders, pers. comm.; Ron Derma, 

pers. comm.). 

For practitioners wishing to more accurately estimate the appropriate number of 

fish to achieve adequate control, the Waterways Experiment Station (WES) of the United 

States Army Corps of Engineers has developed a grass carp stocking rate computer 

model called AMUR/STOCK (Madsen et al. 1998). AMUR/STOCK was developed to 

help aquatic plant managers evaluate proposed stocking rate strategies. Practitioners 

would input data on water body temperature, plant biomass and growth rate, number of 

grass carp initially stocked, and grass carp feeding preference. The model would then 
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determine the required rate of restocking and the plant area controlled (Stewart and Boyd 

1999). AMUR/STOCK is available as part of the Aquatic Plant Information System CDROM, which can be ordered for free from the U.S. Army Corps of Engineers Website 

(U.S. ACE 2001; http://www.wes.army.mil/el/aqua/apis/apishelp.htm)

Grass carp are more effective at removing some plant species than others. Highly 

preferred species include Egeria densa, Hydrilla verticillata, common elodea (Elodea 

canadensis), and duckweeds (Lemna spp. and Spirodela spp.). Non-preferred species 

include coontail (Ceratophyllum demersum) and milfoils (Myriophyllum spp.) (Stewart 

and Boyd 1999). Success has been reported in controlling water hyacinth using a 

combination of grass carp and weevils (Gopal 1987). Eurasian watermilfoil is not a 

preferred food source and grass carp will consume most other aquatic species before 

eating it (Washington State Department of Ecology 2001). Also, grass carp may consume 

submerged species before eating floating species in the same water body (Santha et al. 

1994). 

A number of practitioners in California water bodies have reported positive 

experiences with grass carp. Use of grass carp has been successful for southern California 

irrigation district delivery channels, where the primary management objective is water 

conveyance, and complete elimination of all vegetation is acceptable. For example, grass 

carp have been an important tool in controlling Hydrilla verticillata (hereafter, hydrilla) 

in the Imperial Valley, CA. In the Imperial Irrigation District, hydrilla infested areas have 

been reduced from over 600 miles of irrigation canals, reservoirs, drains, private ponds 

and deliveries to less than 0.75 miles in a single drain. While triploid grass carp remain 

the main weapon against hydrilla, an integrated method of fish, mechanical, and manual 

methods is being used to eliminate the final <1% of the hydrilla infestation (Mike 

Mizumoto, pers. comm.). A total of 13,908 triploid grass carp have been stocked into the 

Imperial Valley waters. By 2000, hydrilla was reported to be eliminated from all sites 

except one drain (Mizumoto 2001). The Bard Irrigation Districts and Coachella Valley 

Water District also report very positive experiences using grass carp in irrigation canals 

(Ron Derma, pers. comm.; Paul Saunders, pers. comm.). In the Bard Irrigation District, 

recent set up costs for a six mile irrigation canal included the purchase and permitting for 

300 fish, and the installation of a concrete grate to reduce the risk of fish escape (Ron 
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Derma, pers. comm.). Finally, a number of southern California and Central Valley golf 

courses have stocked grass carp to control vegetation in their ponds (Paul Beaty, pers. 

comm.). These include the Tulare County Recreation Department and the Woodridge 

Golf Course (just outside of Lodi) (Marty Muschinske, pers. comm.). 

Grass carp have also been successfully employed in Arizona canals used for 

drinking water conveyance, where chemical pesticide application was discontinued. The 

Salt River Project (SRP) delivers a million acre-feet of water annually to 250,000 acres in 

central Arizona through approximately 130 miles of canals and 120 miles of laterals. 

Water usage in the SRP system has shifted from primarily agricultural use to use as a 

drinking water source. As a result, environmental regulations prohibit the use of most 

chemical herbicides. Magnacide H (acrolein) and chelated elemental copper are currently 

the only used chemicals. SRP has used grass carp to control extensive aquatic weed 

growth in most of the canal systems for ten years and has found them to be 

“environmentally friendly and cost effective.” Weed growth and fish populations are 

monitored and fish are moved to maintain effective weed control throughout the system. 

Grass carp have been shown to adequately control aquatic weed growth in the SRP 

(Maldonado 2001). 

Other Herbivorous Fishes 

In addition to triploid grass carp, common carp and tilapia have been added to 

ecosystems to reduce aquatic vegetation. However, these species are not perceived to be 

successful and are not recommended for use as biocontrol agents. Common carp stir up 

the bottom of water bodies, and are generally considered to be a nuisance species. 

Anecdotal reports of use of tilapia in the Coachella Irrigation District (southern 

California) indicated that they did not control growth of aquatic plants and were 

constantly getting stuck in irrigation drains (Paul Saunders, pers. comm.). Tilapia is 

prohibited in California north of Los Angeles County and CDFG does not recommend 

they be used for aquatic vegetation control. 

Fish Biomanipulation 

In addition to the use of herbivorous fish, water resource managers can also 

reduce aquatic plant growth by changing the abundance of fish higher in the food web. 
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This method, often referred to as biomanipulation, is typically used to control growth of 

nuisance planktonic algal blooms and has been most successful in small lakes when 

combined with nutrient input control (John Madsen, pers. comm.). Fish biomanipulation 

may also be appropriate in water bodies characterized by large populations of small fish 

that eat zooplankton. In these lakes, the heavy grazing by planktivorous fish can cause 

low zooplankton abundance, and a consequent reduction in zooplankton grazing rates on 

algae. In these circumstances, it may be possible to indirectly control algal production by 

manipulating the “top” of the food web. Specifically, managers reduce the population of 

smaller fish. Freed up from the predation pressure by the small fish, the zooplankton in 

the lake increase in size and foraging rate. This greater grazing by zooplankton 

consequently reduces the overall abundance of algae in the water body, improving water 

clarity (Carpenter et al. 1987; Carpenter and Kitchell 1988). The water body manager can 

reduce the small fish population either by directly removing the fish from the water body 

(e.g., Annadotter et al. 1999) or by adding a large population of predatory fish, which are 

expected to forage heavily on the smaller fish, thereby reducing their population (Kitchell 

1992). This is most successful when omnivorous, benthivorous fish are controlled at the 

same time (John Madsen, pers. comm.). 

Fish biomanipulation is a difficult management method to implement effectively. 

It typically requires a good understanding of the community structure and chemistry of 

the water body. It is only successful in water bodies with certain community structure 

types. If predatory fish are added to the water body, severe fishing restrictions may be 

necessary to maintain the high populations (Kitchell 1992). Additionally, many factors 

can influence algae growth, causing success to vary considerably from year to year 

(Carpenter et al. 1987). Nevertheless, biomanipulation has been reported to substantially 

improve lake water quality in lakes where other methods have failed (e.g., Annadotter et 

al. 1999). 

We know of no examples of fish biomanipulation attempted in California waters. 

It may be an appropriate method for consideration in drinking water reservoirs, where 

human access and fishing are limited, and there is a good scientific understanding of the 

limnology of the water bodies. 
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Terrestrial Herbivorous Mammals 

Terrestrial herbivores may be used to control emergent and riparian vegetation. 

Goats may be corralled into an area where control is desired using electric fencing, and 

allowed to forage there until vegetation is reduced. A number of private companies 

currently offer goat grazing as a vegetation control option, and irrigation districts such as 

Reclamation District 999 do include goat grazing in their control methods (Bob Weber, 

pers. comm.). Although terrestrial herbivores serve as alternatives to chemical pesticide 

application, water quality may be adversely impacted by the movement of soil and 

sediment following disturbance, as well as goat excretion. One of the Aquatic Pesticide 

Monitoring Program demonstration projects evaluates the cost-effectiveness and water 

quality impacts of goat grazing. 

Gastropod Mollusks 

Introduction of snails or sea slugs is a biocontrol option that has been researched 

for certain aquatic infestations. Cooke et al. (2001) reported that small research 

experiments indicate that snails grazing on biofilm algae may be useful for improving 

growth of desirable aquatic plants. Presumably, the use of these grazing snails would 

increase aquatic vascular plant biomass, thereby resulting in reduced nutrient availability 

for floating nuisance algae, and ultimately improvement in water quality (Scheffer et al. 

1993; Scheffer, 1999). Researchers are currently evaluating a number of sea slug species 

for potential biocontrol of the marine invasive plant, Caulerpa taxifolia. Although the 

slug is very promising as a biocontrol agent, there is considerable political ambivalence 

regarding the introduction of a non-native biocontrol species in marine waters (Meinesz 

1999). Therefore, use of gastropods has not been developed for commercial biocontrol 

application. Snails were extensively researched for biocontrol of hydrilla, but were found 

to be an ineffective control method, and thus were not commercially developed (Bill 

Haller, pers. comm.). Interest in development of snails as a biocontrol agent has been 

limited due to the environmental risk associated with purposeful introduction of prolific 

generalized herbivores. Additionally, there is concern that snails can serve as vectors for 

certain fish parasites (McCann et al. 1996). Thus, although gastropod mollusks may have 

potential for use in biocontrol, there is yet to be an example of successful field-scale 

application. 
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Insects 

Another alternative in biological control is the release of insects that specialize in 

feeding on particular nuisance plant species. In other states and countries, insects have 

been developed for biological control of a number of aquatic and emergent plants that 

occur in California waters. These include hydrilla, Eurasian watermilfoil, water hyacinth, 

giant salvinia, and purple loosestrife. In California, insects have been evaluated for 

biological control of hydrilla and water hyacinth, but not for Eurasian watermilfoil or 

purple loosestrife. Currently, the weevil, Cyrtobagous salviniae, is being evaluated for 

long-term control of giant salvinia (Salvinia molesta) on the Colorado River and adjacent 

irrigation drains (Olson 2003). 

Biological control using insects has had limited field application in California 

waters, but has been reportedly successful for plant management in some other states. In 

Florida and Louisiana, biological control of water hyacinth has been successful using two 

weevil species of the genus Neochetina and one moth of the genus Sameodes. However, 

large-scale reduction of water hyacinth (50-70% reduction in plant growth) often took 

years to occur (Bill Haller, pers. comm.). Another concern is that even though plant 

height and flowering might be reduced, the expansion of the plant mat could still occur 

(John Madsen, pers. comm.). 

In California, insects have been tested for control of water hyacinth and hydrilla. 

In an effort to control water hyacinth in the Sacramento-San Joaquin Delta, three species 

of insects were released in 1982. Recent surveys have shown that one of the species 

(Neochetina bruchi, the water hyacinth-eating weevil) has spread throughout the Delta, 

but the populations are not of sufficient size to effectively control the hyacinth. Currently, 

a research collaboration among CDBW, CDFA, and the USDA is underway to 

understand the factors limiting the success of insect biocontrol in the Delta (USDA and 

CDBW 2003). 

Two insect species have been evaluated for control of hydrilla in California, the 

hydrilla tuber weevil (Bagous affinis) and the Asian hydrilla leaf mining fly (Hydrellia 

pakistanae). Laboratory and field studies have determined that both species feed on 

hydrilla tissue and have the potential to reduce hydrilla densities (Godfrey and Anderson 
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1994; Godfrey et al. 1994; Godfrey et al. 1995). However, hydrilla eradication in the state 

is currently achieved using chemical application, grass carp, hand removal, and sediment 

dredging for tubers. 

Biological control has shown some success in controlling Eurasian watermilfoil in 

other states, though the control agents have not been introduced in California. The milfoil 

weevil (Euhrychiopsis lecontei) appears to be able to control Eurasian watermilfoil, 

causing significant biomass reduction in the laboratory (Creed and Sheldon 1993) and in 

the field (Creed and Sheldon 1995). This insect exposes vascular tissue of the stem when 

feeding on Eurasian watermilfoil and causes the collapse of the plant. Sheldon and 

O’Bryan (1996) have shown that the weevil preferred Eurasian watermilfoil. Their data 

from the six years following a Eurasian watermilfoil decline in a Vermont lake show that 

watermilfoil has not regained its dominance, while native plant density has increased. 

The increase in native plant density may result from poor egg hatching and recruitment 

on non-target plant species (Sheldon and Creed 2003). 

Biological control using insects or other invertebrates does not appear to hold 

much promise for Egeria densa. Many organisms were tested to control Egeria densa

(including snails), but generally showed little success (Bill Haller, pers. comm.). 

Often times, insect population growth may not be sufficient to achieve biological 

control in weed-infested areas. Evaluation of feasibility is often required on a sitespecific basis. For example, the milfoil weevil appears to have much lower densities in 

waters with cooler temperatures, and might not be suitable for regions with colder 

summer climates. Another important consideration is the potential for effects on nontarget species or other unintended consequences of the insect introduction (Sheldon and 

Creed 2003). Non-native insect species, once introduced to a new region, could 

potentially spread rapidly and adversely affect local ecosystems. They could potentially 

impact non-target vegetation and cause loss of habitat for some fauna. Site-specific 

research on the specific impacts of a particular biocontrol insect should be conducted 

before that agent is introduced to California waters. 
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Predatory Animals For Mosquito Control 

A number of predatory fishes and invertebrates are available or in development 

for controlling mosquitoes. These organisms prey upon mosquito larvae or pupae, 

thereby reducing reliance on chemical pesticide application for mosquito control. In 

California, mosquitofish (Gambusia spp.) are readily available for mosquito control. 

Gambusia are very effective predators on mosquito larvae, with some species even able 

to reduce mosquito populations in dense beds of aquatic plants (Lounibos et al. 1992). 

Additionally, a number of predatory fish and invertebrate species are currently being 

applied on a pilot or local basis by various California Mosquito and Vector Control 

Districts (Karl Malamud-Roam, pers. comm.). 

In addition to mosquitofish, at least three fish species are currently being studied 

for biological control in California waters: guppies (Poecilia reticulate), Sacramento 

perch (Archoplites interruptus), and three-spined stickleback (Gasterosteus aculeatus)

(Miller 2003; Schon 2003a, b). The Sacramento-Yolo Mosquito and Vector Control 

District (SYMVCD) has stocked guppies in 286 mosquito sources, comprising 670 acres. 

Permitting for guppies was relatively easy for guppies in northern California waters, 

because they do not survive the cold winters and are therefore unlikely to have long-term 

adverse impacts on native wildlife. They are relatively easy to culture and more tolerant 

of adverse environmental conditions than mosquitofish, making them appropriate for 

stocking in dairy lagoons and acidic creeks (Schon 2003a). SYMVCD has had limited 

success with three-spined stickleback. Although they can be cultured and do consume 

mosquito larvae in the laboratory, the sticklebacks are not effective at consuming 

mosquito larvae in many field conditions (Schon 2003b). Sacramento perch are still in the 

development and testing phase for mosquito control by the Contra Costa Mosquito and 

Vector Control District. They have been successfully raised and consume mosquito 

larvae in the lab, but large-scale experiments or field applications have yet to be 

conducted (Miller 2003). 

An additional fish genera, the pupfish (Cyprinodon spp.) has been proposed for 

evaluation, but practical use for mosquito control is restricted due to special status (Su 

2003a). In the Coachella Valley (southern California desert), a species of tadpole shrimp 

(Triops newberryi) has been extensively evaluated in laboratory studies. The tadpole 
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shrimp shows promise for mosquito control in ephemeral habitats. Tadpole shrimp have a 

number of desirable traits for mosquito control in intermittently wetted habitats; they prey 

on mosquito larvae, have a desiccation resistant life stage, grow quickly, and have high 

reproductive capacity. Nevertheless, they have yet to be evaluated in large-scale field 

applications (Su 2003b).

Commercially Available Biocontrol Agents 

Biological agents such as bacteria, viruses, and enzyme solutions are 

commercially available to aid in the improvement of water quality. These agents are 

touted to increase water flow by reducing/eradicating algal, and to some extent, 

macrophyte growth. Few field and lab experiments have been completed to test the 

efficacy of commercial microbial products. Commercial microbial products generally 

contain a mixture of bacteria and enzymes. The microbial products are typically applied 

to the system to augment the system’s bacterial populations. The theory is that increased 

bacterial concentrations will limit the availability of nutrients necessary for algal and 

macrophyte growth and reproduction. The bacteria, theoretically, utilize the same 

nutrients (nitrogen and phosphorus) as the photosynthesizers and therefore act as 

competitors for growth. 

Biocontrol agents are readily available as commercial formulations. Examples 

include Aqua 5TM , 1998 LakePakTM, WSPR , Algae-TronTM , and PK-700, all of which 

are relatively inexpensive to purchase. Nevertheless, the success of biocontrol agents to 

reduce primary producer (planktonic) populations is not well established. Few studies 

are available testing the effectiveness of these methods. The available peer-reviewed 

studies indicate that microbial control methods are not effective for control. Some 

laboratory research has piloted new methods, such as culturing and expanding the 

bacterial fauna from individual lakes. But the practicality and cost-effectiveness of these 

methods for field application remains to be tested. Mesoscale experiments are necessary 

to see if laboratory results can be replicated in the field. 

A recent laboratory and field study provided evidence that commercially available 

biocontrol agents were generally not effective for control of algal growth (Duvall et al. 

2001; Duvall and Anderson 2001). In the laboratory study, there was no significant 
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decrease in chlorophyll-a concentrations in the treated systems, compared to control 

systems where no microbial product was added (Duvall et al. 2001). In the field study, 

lake mesocosms treated with commercial microbial product were measured for bacteria 

concentrations. One out of the three commercial products applied showed a significant 

increase in bacteria concentrations when compared to the controls but none of the 

commercially treated mesocosms showed a significant decrease in chlorophyll-a 

concentrations when compared to controls (Duvall and Anderson 2001). A study by 

Queiroz and Boyd (1998) also indicated no relationship between addition of bacterial 

agents and chlorophyll concentration in the water body. Bacterial inoculate were added 

to catfish aquaculture ponds. There was no significant difference in chlorophyll-a 

concentrations between treated and control ponds and no difference in bacterial 

populations between treated and control ponds. The treated ponds produced a higher net 

production of catfish than the non-treated ponds, but the reason for this was unclear. 

Plant Pathogens Currently In Development 

Plant pathogens for the control of hydrilla and Eurasian watermilfoil have shown 

progress over recent years but remain in the research phase. So far, only laboratory tests 

in aquariums and small ponds have been conducted, and the methods are not available for 

widespread application. The use of the pathogen Fusarium graminearum in control of 

Egeria species is in the pre-commercial evaluation phase (Charudattan and Dinoor 2000). 

The fungus Alternaria eichhorniae has shown some success in control of water hyacinth 

in Africa but rapid colonization by the fungus is necessary for long-term control (Reeder 

2003). Species of Rhizoctonia have the ability to kill plants but there is no host 

specificity and non-target plants can also be affected. 

Since the 1980s, the Corps of Engineers (USACE) has been researching plant 

pathogens to control hydrilla in the Southeastern U.S. A fungal pathogen species from 

Texas (Mycoleptodiscus terrestris) holds promise for future control but is not yet 

commercially viable (Judy Shearer, pers. comm.). So far, only laboratory testing in 

aquariums (up to 67,000 l) and small pond testing have been conducted since the USACE 

does not have the permit required for larger scale fieldwork. Whether these agents will be 

successful in flowing waters or large-scale applications remains to be tested. New 

methods have been developed to bind the organisms to plants. These new formulations 
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include flour or starch and oil that apply buoyancy and keep the fungus attached to 

hydrilla. The USACE is working with the SePRO Corporation on patenting the microbial 

herbicide (Judy Shearer, pers. comm.). 

Hydrilla has also been evaluated for integrative control combining fungal agents 

with herbicides. Laboratory studies indicated that use of Mycoleptodiscus terrestris in 

combination with the herbicide fluridone reduced hydrilla biomass by more than 90% and 

was more efficacious than these treatments individually (Netherland and Shearer 1996; 

Nelson and Shearer 2002). Mesocosm studies had similar results (Nelson et al. 1998). 

Sublethal amounts of herbicide were applied which would also minimize the impact on 

non-target species if used in natural environments. Shearer and Nelson (2002) found that 

application of a combination of M. terrestris and the chemical herbicide endothall also 

reduced hydrilla biomass in lab experiments. Shearer (2002) also noted that stressful 

conditions, such as herbicidal application in non-lethal doses, may weaken a plant and 

compromise a plant’s defenses, thereby making it more susceptible to infection by the 

fungus. 

Integrative control has been evaluated for water hyacinth using multiple insects or 

insects in combination with bacterial pathogens (Gopal 1987). Co-introduction of 

Neochetina eichhorniae and Orthogalumna terebrantis reduced plant density by 45% 

and petiole length by 35% over a 50-week experimental period. Integrative control has 

also been applied to water hyacinth management. The pathogen Cercospora rodmanii

and Neochetina eichhorniae eliminated 99% of water hyacinth (Charudattan 1984, as 

reviewed in Gopal 1987). 

The permitting process for plant pathogens is fairly extensive, which can delay 

and limit development of these alternatives. Endemic plant pathogens need to be 

registered with EPA before release in the environment. The registration process requires 

intensive host specificity and toxicity testing. After that is accomplished, the pathogen 

species gets a label, just like a chemical, with established maximum applications rates 

and use restrictions. Costing about $2 million, plant pathogen registration is less costly 

than chemical registration (about $20 million) (Judy Shearer, pers. comm.). Further 

development and registration of plant pathogens has been slowed by lack of funding and 
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interest on the part of major corporations or venture capitalists (Rahavan Charudattan, 

Pers. comm.; Judy Shearer, pers. comm.). 

Pathogens For Mosquito Control 

Pathogens have also been studied for mosquito control. The microbial organism, 

Lagenidium giganteum shows promise for reducing larval populations of Mansonia 

mosquitoes. In a study by Cuda et al. (1997), L. giganteum reduced the emergence of 

adult mosquitoes, and appeared to generate self-sustaining populations in test pools. This 

pathogen has specific water quality requirements and is only likely to be effective in 

relatively unpolluted water bodies. 

Cyanobacteria Control Agents Currently in Development 

In laboratory and microcosm experiments, specialized biological control agents 

have shown success in the control of nuisance cyanobacterial blooms. Methods under 

development include cyanophages, bacteria, and cell culture isolates (reviewed in Sigee 

et al. 1999). However, many of these agents are still in the research phase, and it may be 

years before they become available to practitioners. 

Cyanophages (viruses) may be useful in controlling cyanobacterial blooms. 

Cyanophages are host specific, so a variety of species would be necessary for biocontrol. 

Ultimately, the cyanobacteria species may become resistant to the cyanophages, 

rendering the control method ineffective in the long term. Bacteria can kill cyanobacteria 

by producing extra cellular products that lyse cells (i.e., cause them to “blow up”). Some 

fungal species can produce an antibiotic that also harm cyanobacteria, but physical 

proximity between fungi and cyanobacteria is necessary. Isolates from cultures of the 

aquatic fungus, actinomycetes, have shown inhibitory effects against cyanobacteria. The 

isolates are collected from environmental samples and isolated in the lab. Streptomyces 

exfoliatus was successful in lysing genera of major bloom species such as Anabaena, 

Microcystis and Oscillatoria. Microcosm studies show that S. exfoliatus was successful 

in lysis of lake phytoplankton and a reduction of algal populations. Protozoans reduce 

cyanobacterial cells by grazing. Lab experiments have shown that certain protozoan 

species graze on genera of oscillatoria and anabaena. Microcosm experiments have 

shown a reduction in algal populations. 
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Organic Material Amendment 

Organic materials, such as peat, and barley straw, have been used for control of 

rooted aquatic plants and algae. Theoretically, control is achieved by reduction of nutrient 

availability to the nuisance species or release of chemicals that impede growth. Organic 

material amendment results tend to be system specific, creating a need for small-scale 

pilots prior to widespread application in a specific water body. 

Field studies have shown that sediment amendment with peat or barley straw may 

reduce hydrilla production (Spencer et al. 1992). A number of laboratory studies have 

demonstrated that natural or human-altered increases in sediment organic matter content 

can reduce growth of Eurasian watermilfoil (Barko et al. 1986; Gunnison and Barko 

1989). The chemistry of added organic materials can affect their ability to reduce aquatic 

plant growth; organic material may inhibit plant growth or stimulate plant growth, 

depending on the nitrogen content of the added organic materials (Spencer et al. 1992). 

The use of organic additions, including barley straw, for the control of hydrilla has not 

been widespread. 

Barley straw has gained popularity in recent years for algae control via word-ofmouth successes, but research indicates that it only works in certain management 

circumstances (Lembi 2002). The activity of barley straw is usually described as 

preventing the new growth of algae, rather than killing algae already present. It is thought 

that fungi decompose the barley in water, which causes lignin- and tannin-derived 

polyphenolic compounds to be released, preventing the growth of algae. This method is 

most successful in well oxygenated water bodies where the decomposition of barley is 

not disrupted (Boylan and Morris 2003). Martin and Ridge (1999) and Terlizzi et al. 

(2002) suggest that decomposing barley may inhibit the growth of a limited number of 

algae and dinoflagellate species under both laboratory and field conditions. Barley straw 

has also shown some success in the control of cyanobacterial growth (Barrett et al. 1996). 

Because effectiveness of barley straw to control algae will vary from site to site, smallscale pilot studies should be conducted before investing significant time or effort in 

whole-lake applications. 
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Managers can also add barley straw to sediments, in an effort to control growth of 

rooted aquatic plants. Other materials, including sand, gravel, and peat, have also been 

added to sediments to alter plant growth (Barko et al. 1986; Spencer et al. 1992). Plants 

grow best with a certain amount of nutrients in the sediment (Barko and Smart 1986). 

Addition of barley straw, peat, or other organic material may inhibit aquatic plant growth 

by bringing the nutrient density and concentration out of the ideal range (Systma and 

Parker 1999). As with floating algae, the ability of barley straw to control growth of 

rooted aquatic plants varies among studies and locations. Parker and Sytsma (1998) 

found good evidence that addition of barley straw reduced Potamogeton growth in 

Oregon irrigation canals. In contrast, Spencer et al. (1992) found that barley straw or peat 

can actually increase hydrilla growth in California soils. Water hyacinth and other freefloating plants that prefer acidic water for nutrient uptake may also benefit from organic 

additions to the water body (John Madsen, pers. comm.). As with control of algae, smallscale pilot studies should be conducted to evaluate effectiveness before applying at a 

management scale. 

Although barley straw may be a viable algae control method, it has uncertain legal 

status for use by public water body management practitioners (Lembi 2002). The EPA 

states that a pesticide is “any substance or mixture of substances intended for preventing, 

destroying, repelling, or mitigating any pest.” However, no company has ever registered 

barley for use as a pesticide as it has not gone through the testing required for 

registration. Therefore, barley cannot be sold as a pesticide to control algae. Its use in 

private ponds or lakes is allowed under the facet that it qualifies as a “home remedy”, its 

use as a commercial algaecide in larger or public bodies of water is not supported by the 

EPA (Lembi 2002). Despite the non-qualification of barley straw as an official pesticide, 

it is still widely sold on the commercial market, approved by the New York State as a 

method to improve the quality of garden ponds (Lembi 2002). 

Acetic Acid 

The addition of dilute acetic acid to the propagules, root crowns, or tubers of 

aquatic weeds has shown to be a successful growth inhibitor (Spencer and Ksander 

1995a, 1995b, 1997, 1999; Parker and Sytsma 1998). Submersed aquatic plants, such as 

hydrilla, rely on subterranean vegetative propagules, such as tubers, turions, or winter 
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buds for reproduction. These propagules enable the plant to survive periods of 

unfavorable conditions. The addition of acetic acid to these propagules at the appropriate 

time in their life cycles was shown to limit growth of these weeds. The growth of both 

hydrilla and sago pondweed (Stuckenia pectinatus) can be decreased as a result of 

exposure to dilute acetic acid (Spencer and Ksander 1995a, 1995b, 1997, 1999; Parker 

and Sytsma 1998). Acetic acid sediment amendment will only be effective in channels 

with little or no standing water; therefore, natural or artificial water level drawdown is 

generally necessary for this method (Parker and Sytsma 1998). 

At this time, we know of no California field practitioners who use acetic acid to 

control growth of rooted aquatic plants. Field studies have shown that it was effective in a 

Yuba County canal (Spencer and Ksander 1999), though cost effectiveness for 

widespread application has not been determined (David Spencer, pers. comm.). 

Preliminary research trials by the USDA-ARS and the Invasive Spartina Project have also 

shown that acetic acid may hold promise for killing rhizomes of smooth cordgrass 

(Spartina alterniflora) (Anderson 2003). A sanitary district in Humboldt County has been 

evaluating acetic acid for control of floating vegetation in some of their treatment ponds. 

An ongoing APMP demonstration project is underway to evaluate its effectiveness and 

environmental impacts in control of duckweed (Lemna spp.) growth (Mark Bryant, pers. 

comm.). In Kansas, acetic acid can be an effective contact herbicide for common weeds 

in agricultural field plots (Lee DeHaan, pers. comm.). As with barley products, acetic 

acid has not been registered or formally tested for use as a pesticide, so it has uncertain 

legal status. Increased acidity in the water body may have severe effects on non-target 

aquatic organisms. 

Management Considerations For Organic Material Amendment 

All of the organic material amendment techniques can be difficult to apply at 

large management scales. Barley straw added to the water column tends to float on the 

surface, which can lead to homeowner complaints. Attempts to contain the barley straw 

in sacks can reduce effectiveness (Tom Jordan, pers. comm.). Commercial products, such 

as barley pellets, barley straw bales, “pond pads”, and barley extract are readily available 

(Jane Sooby, pers. comm.). They can be purchased on the World Wide Web or ordered 

through pond management magazines, such as Doctors Foster Smith 
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(www.DrsFosterSmith.com) or Water Gardening (www.watergardening.com). A half 

pound of barley straw ranges in cost from $5-$15, and marketers claim this amount can 

be used to treat 500 to 1000 gallons for approximately 6 months. Barley hay can also be 

purchased in bulk from agricultural sources for only $1 - $3/bale. In urban areas, storage 

may not be readily available for bulk quantities (Tom Jordan, pers. comm.). Sediment 

amendment is typically applied in dewatered systems, because materials like barley straw 

tend to float. Development of techniques to produce barley straw slurries or other easily 

spread materials may improve application efficiency and effectiveness (Parker and 

Systma 1998; Systma and Parker 1999). Although acetic acid is relatively inexpensive to 

purchase, it can be dangerous to handle in concentrated form. Concentrated acetic acid 

can cause burns to skin and eyes, requiring protective clothing, and appropriate 

environmental conditions for use (Parker and Sytsma 1998). 

Plant Competition 

Nuisance aquatic plant impacts may be reduced by introduction or augmentation 

of other plant populations. The more desirable plants may compete with nuisance species, 

thereby impeding their growth and spread. Nevertheless, the addition of competing plants 

remains a highly experimental procedure with limited field applications or assessments of 

effectiveness (Holdren et al. 2001). The best results will be seen when the nuisance plant 

is controlled before the native plant is added in order to prolong the effectiveness of the 

initial control technique (John Madsen, pers. comm.). 

In a Massachusetts lake, native Chara sp. was experimentally planted in areas 

harvested for Eurasian watermilfoil. The researchers found that areas with transplanted 

Chara plants remained resistant to milfoil invasions over the duration of the two-year 

study (Monnelly et al. 2003). For selected Wisconsin water bodies, The Nature 

Conservancy plants shoreline areas with wild rice, a native emergent plant. The 

replanting efforts are perceived as successful methods of reestablishing native vegetation 

(Hannah Spaul, pers. comm.). Spikerush (Eleocharis spp.) has had some success in 

crowding out nuisance plant species in many aquatic systems, including irrigation 

drainage canals (Sytsma and Parker 1999). Spikerush has a low growth habit and 

negligible effect on water flow, which are desirable characteristics. There is also some 

evidence that these plants secrete a growth inhibitor that is absorbed by surrounding 
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plants. Slender spikerush (Eleocharis acicularis) may be more suited for California 

water bodies. 

PHYSICAL AND MECHANICAL CONTROL METHODS 

This section includes all methods that involve destruction or removal of nuisance 

plants by physical or mechanical methods. Mechanical methods include harvesting, 

cutting, rotovation, weed raking, hand pulling, dredging, channel clearing, and 

excavation. All of these methods involve direct damage to the target nuisance species 

(typically aquatic plants) by physical removal or destruction. Physical methods also 

involve physically manipulating the water body or immediate plant environment to 

reduce survival or growth of the nuisance species. 

Mechanical Harvesting 

Mechanical harvesters are large machines which cut and collect aquatic plants. 

They remove the upper portion of the plant and are able to cut five to ten feet below the 

water surface. The weeds collected by the harvester can then be transferred to an upland 

disposal site. Harvesting immediately removes surface mats of plants and opens up the 

area, which can help maintain boat lanes. Due to the size of the machines, only larger 

areas with a sufficient depth are suitable for this treatment. The same area may need to be 

treated twice or more per growing season to maintain control of the nuisance weed 

(Kimbel and Carpenter 1981; U.S. Army Corps of Engineers 2002). 

Mechanical harvesters are currently available in California, with several 

contractors offering these services and harvesters available for purchase from local and 

national companies (Appendix A). Several companies commercially produce harvesters, 

including Aquarius Systems (http://www.aquarius-systems.com) and Aquamarine 

(www.aquamarine.ca). PMC Production, a California based company, produces 

harvesters commonly used by local contractors (http://www.pmcproduction.com/). Miller 

Aquatic Technologies actively markets some of their harvesters as cost effective for 

management on canals, small ponds, and other narrow and shallow waterways 

(http://www.milleraquatics.com/harvesters.html). 

In other parts of the country, harvester technology has developed to provide 

specialized responses to local plant management concerns. For efficient control of plant 
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problems in the very large waterways of Florida, large-sized harvesters have been 

developed. Harvesters used in Florida reach up to 95 feet in length and work very 

efficiently in large-scale projects (Bill Haller, pers. comm.). Although such large 

harvesters may not be appropriate for many California water bodies, they may be useful 

for managing Salvinia molesta in the Colorado River. 

A significant problem with mechanical harvesting is the often rapid regrowth of 

the plant after harvesting. In a study of Eurasian watermilfoil control in a Minnesota lake, 

total shoot biomass and plant abundance was only reduced for six weeks following the 

harvest (Crowell et al. 1994). Plant growth rates were higher in the harvested areas than 

unharvested areas. As a result of the rapid regrowth, harvesting must be conducted 

multiple times in a growing season to achieve adequate control. For example, in a 

Wisconsin lake, monthly or bi-monthly harvesting was most successful for controlling 

Sago pondweed (Madsen et al. 1988), a plant common throughout California (DiTomaso 

and Healy 2003). In some water bodies, multiple harvesters must be operated daily 

during the growing season to fight off the constant plant regrowth (e.g., Lake 

Minnetonka Conservation District 2002). Local municipalities, such as the City of 

Oakland, often purchase and maintain their own harvesters to achieve this constant 

control. 

Sometimes, specialized mechanical harvesting innovations can increase control 

efficiency, thereby reducing frequency of harvesting required. In particular, cutting at the 

base of the plant stem can dramatically reduce regrowth rate. In Wisconsin, a mechanical 

harvester was modified with a blade that could cut Eurasian watermilfoil to within 0.6 m 

of the sediment surface (Unmuth et al. 1998). Long-term control was achieved in deep 

waters (greater than three meters), where 46% of cut channels persisted for three years 

after the study. Control was less effective in shallow waters (less than three meters), with 

only four percent of channels remaining clear. One of the Aquatic Pesticide Monitoring 

Program demonstration projects will evaluate a mechanical cutter designed to remove 

plants at the root, which may also reduce plant regrowth rate (Ross Holton, pers. comm.). 

Timing and frequency of harvesting may also affect the regrowth of the nuisance 

species. In Wisconsin, harvests in autumn are likely to cause strong reductions in 
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Eurasian watermilfoil total non-structural carbohydrates (carbohydrates used for future 

growth), and consequent regrowth rate (Kimbel and Carpenter 1981). In a Florida study, 

repeated clipping of hydrilla stems significantly reduced rate of producing reproductive 

tubers. Tuber reduction was more pronounced when plants were clipped prior to 

formation of a dense canopy. This result suggests that repeated harvesting during tuber 

forming time-periods may reduce hydrilla recruitment (Fox et al. 2002). 

Disposal is a very difficult issue with wide scale harvesting applications such as 

the Sacramento-San Joaquin Delta (Cynthia Gause, pers. comm.). Disposal costs 

constitute almost 25% of the annual harvesting budget for control of Eurasian 

watermilfoil in Tahoe Keys (Greg Tischler, pers. comm.) In Florida, large harvesting 

machines dispose the plant material in areas of the same water body since launching and 

on-land disposal would dramatically increase cost (Bill Haller, pers. comm.). CDBW has 

met with substantial permitting difficulty in their efforts to dispose of plant material on 

levees or other locations near Delta water bodies. For example, the Central Valley 

Regional Water Quality Control Board (CBRWQCB) mandated that they obtain written 

approval from individual landowners, prior to disposing of plant materials on levees. The 

CBRWQCB also determined harvested plant materials to become waste discharges once 

removed from the water, creating difficulties in NEPA and CEQA permitting (Cynthia 

Gause and Marcia Carlock, pers. comm.). Although not insurmountable, permitting issues 

do delay the implementation of harvesting projects in sensitive areas like the Delta. 

The Waterways Experiment Station (WES) of the Army Corps of Engineers has 

developed computer programs to assist managers in developing effective mechanical 

harvesting plans. The HARVEST program, developed by WES, will simulate the cutting, 

collection and transport of a nuisance species in an aquatic system (Madsen et al. 1998). 

It has been used in California to determine the current production capacity of harvesters 

operating on Big Bear Lake, and to identify locations where new offloading sites could 

be developed to increase harvesting efficiency (ReMetrix 2001). HARVEST is available 

for free by ordering a CD-ROM copy of APIS (Aquatic Plant Information System) from 

WES. APIS is an interactive CD-ROM that provides information on aquatic nuisance 

species, their distribution, and the current control methods available (U.S. Army Corps of 

Engineers 2001; http://www.wes.army.mil/el/aqua/apis/apishelp.htm). 
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Peer reviewed studies are lacking on the cost-effectiveness and environmental 

impacts of harvesting in California waters. However, a number of successful harvesting 

programs currently exist in California. One example is mechanical harvesting of Sago 

pondweed in Clear Lake, CA. At three locations in Clear Lake, mechanical harvesting 

was conducted in a combined area of about eight acres. Approval was obtained from the 

Lake County Department of Agriculture to assure that there would be no interference 

with active hydrilla control. It was reported that a boat that followed the cutter retrieved 

about 80% of the cut weeds. The only observed fish mortality was one small catfish. The 

subsequent clean up was messy, as about 15 cubic yards of fragments were removed from 

the shoreline. Overall, it was stated that mechanical harvesting was an effective method 

for nuisance control with immediate results (Lake County Water Resource Division 

1999). Mechanical harvesting programs are also actively employed by the Tahoe Keys 

Property Owners Association (Greg Tischler, pers. comm.) and the City of Oakland (for 

Lake Merritt; Richard Bailey, pers. comm.). Many estuarine and inland water bodies, 

such as Lake Van Ness (City of Visalia), Winchester Lake (Reclamation District 999), 

Westlake Lake (City of Westlake), and San Mateo Lagoon (city of San Mateo) are 

managed by contracts with private contractors (Dave Najara, pers. comm.; Tom McNabb, 

pers. comm.; George Forni, pers. comm.; Bob Weber, pers. comm.). 

Harvesting and removing cut plant material may be preferable to leaving plant 

material in place in eutrophic (high nutrient) systems, because it may decrease the 

amount of nutrients available for primary production. Carpenter (1980) predicted that 

half of the flux of dissolved total phosphorus (DTP) and dissolved organic material 

(DOM) from the littoral zone (shallow area) to the pelagic zone (open water) is from the 

decay of aquatic plants. The prediction, based on a eutrophic hard water lake in 

Wisconsin, suggests that aquatic plants can compose a substantial pool of nutrients that 

mechanical cutting would free up for algal growth. Harvesting of macrophytes removed 

37.4% of the annual phosphorous inputs and 16.4% of nitrogen inputs to a eutrophic lake 

in Wisconsin during a late August harvest (Carpenter and Adams 1977). This may 

decrease within-lake nutrient levels but does not decrease the external loading of 

nutrients to a water body. Although harvesting may decrease within-lake nutrient levels, 
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algae production may continue to remain high due to high external loading or nutrient 

release from sediments. 

The price per acre of mechanical harvesting may range from $500-800, excluding 

mobilization, and the cost for equipment purchase ranges from $35,000 to $110,000 

(Washington State Department of Ecology 2001). Regular harvesters can remove plants 

at rates of approximately one to four acres per day, depending on the size of the machine 

and plant density (John Madsen, pers. comm.). Larger water bodies with widespread 

infestations may require several harvesters to achieve plant control (e.g., Lake 

Minnetonka Conservation District 2002). Disposal options and fees are another 

consideration. Sometimes permits have to be obtained to dispose the plant biomass and 

disposal fees apply for landfill sites. 

Environmental Effects of Mechanical Harvesting 

Mechanical harvesting operations can have impacts on water quality, fish 

survival, and future distribution of problem weeds. Unlike many mechanical control 

methods, the environmental impacts of harvesting have been evaluated extensively in 

numerous studies. 

Water body nutrient concentrations may be reduced by the harvesting and 

removal of plants (Carpenter and Adams 1977). Harvesting may initially increase the 

turbidity and dissolved solid concentration of a system (Alam et al. 1996). In some cases, 

harvesting may have no short-term impacts on water quality. For example, Carpenter and 

Gasith (1978) found no significant difference in particulate phosphorus, total Kjeldahl 

nitrogen, DOC, BOD or dissolved reactive phosphorus between control and cut plots in a 

eutrophic lake. In the longer term, harvesting can reduce internal loading of dissolved 

phosphorus that occurs via natural macrophyte senescence (Carpenter 1983). 

Nevertheless, the amount of nutrients removed in a typical harvesting program is usually 

much less than the total rates of internal nutrient recycling and external loading to a water 

body (John Madsen, pers. comm.). In contrast, chemical application may increase internal 

phosphorus loading by plant senescence (Carpenter and Adams 1978). Ultimately, 

harvesting may slow succession of highly eutrophic lakes (Carpenter 1981). 
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Harvesting is not recommended for fast moving waters, due to the potential risk 

of spreading an invasive plant species. Harvesting is also not advisable in water bodies 

with early infestations of plants that spread by fragmentation. Plant species of particular 

concern include Eurasian watermilfoil (Myriophyllum spicatum), parrotfeather 

(Myriophyllum aquaticum), hydrilla (Hydrilla verticillata), and Brazilian egeria (Egeria 

densa) (John Madsen, pers. comm.). There is evidence that standard harvesting 

operations release viable fragments of Egeria densa in the Delta (Anderson et al. 2000). 

If fragments of plants are not captured by the harvester, they can be hand collected to 

eliminate the possibility of spreading the plant parts to new areas. If all available niches 

are infested already, harvesting is an option to be considered to reduce plant biomass, 

while leaving the bottom part of the plant intact for habitat as well as sediment 

stabilization. In Clear Lake, permits from the Department of Food and Agriculture will 

only be issued for harvesting in areas more than 1⁄4 mile away from sites infested with 

hydrilla (Nate Dechoritz, pers. comm.). 

Mechanical harvesting can have both negative and positive effects on aquatic life. 

Harvesting can result in direct mortality to and removal of fish, invertebrates, and turtles 

(Mikol 1985; Booms 1999; Madsen 2002). Booms (1999) estimated that 39,000 fish and 

700 turtles were removed during the harvesting of a Wisconsin lake from May thru mid 

August. Unmuth et al. (1998) estimated that 36 fish/hectare were removed in a harvest. 

Nevertheless, these removals of small fish and invertebrates may have limited impacts on 

the overall populations. For example, Armitage et al. (1994) found no significant 

difference in macroinvertebrate richness or abundance between stream areas treated with 

chemicals or by harvesting. Monahan and Caffrey (1996) found that mechanical cutting 

reduced macroinvertebrate community composition and abundance more than chemical 

treatment but abundance increased rapidly after cutting and there were no observable 

effects to fish. 

Part of the effect of harvesting is the alteration of underwater habitat. Garner et al. 

(1996) indicate that after cutting, reduction in available plant cover causes declines in fish 

growth and Cladoceran densities. When applied to create habitat variation, harvesting 

can positively affect growth of some fish species. For example, when channels are 

created to enable access of predatory species, harvesting can reduce stunting of smaller 
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fish. Olson et al. (1998) found that creating deep lake channels by harvesting increased 

the growth rates of some age classes of bluegill and largemouth bass. Another strategy to 

create variation in habitat is to harvest in alternating sections of a water body with 

alternating years. For example, in a river or canal where water delivery is needed, a 

channel may be cut adjacent to opposite banks on alternating years (Garner et al. 1996). 

Harvesting may also impact plant diversity in lake systems. Species diversity was 

found to be greater in unharvested areas than harvested areas in Lake Wingra, Wisconsin 

(Nichols and Lathrop 1994). Long-term monitoring of harvested lakes in Wisconsin 

showed a decrease or no change in the number of native species and a decline or no 

change in the watermilfoil frequency (Helsel et al. 1999). 

Mechanical Cutting 

Mechanical weed cutters can cut plants several feet below the water surface or 

can cut emergent plants above the water surface. The distinction between mechanical 

cutting and mechanical harvesting is that while harvesters remove cut plant material from 

the water body, mechanical cutting machines do not remove the cut plant material. 

Therefore, the cutters can operate demonstrably faster compared to harvesters. Generated 

floating plant fragments may be removed from the water to prevent them from re-rooting 

or drifting. Clean up can be accomplished using a weed rake or specially designed nets. 

As with harvesting, areas may need to be cut several times during the growing season. 

In limited circumstances, cut plants may be left in the water to decompose. This 

significantly reduces control costs because removal, off-loading, and disposal are not 

required in these situations. This method usually requires shredding of the plants into 

small pieces. It is only appropriate for species not likely to spread by fragmentation, or in 

dense infestations requiring rapid control. However, the cut vegetation may increase 

water column nutrient concentrations and turbidity (James et al. 2002). 

Recent mechanical cutting technologies not readily available in California waters 

include “juicers” and highly efficient mechanical shredders. Several demonstration 

models have been developed of the “juicer” or “grinder”, which grinds the cut plant 

material to a fine pulp and thereby is believed to create non-viable fragments. The 

addition of nutrients to the water column may be a concern (William Haller, pers. comm.;
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John Madsen, pers. comm.). Most models of this system are prototypes that are not 

widely available for commercial use. One model, “the Crusher,” will be evaluated as part 

of an APMP (Aquatic Pesticide Monitoring Program) demonstration project in 2004. 

Shredding machines may be a cost-effective, large-scale operating alternative to 

harvesters. The shredded plant material is left in the water, and effects of decomposing 

plants to the water chemistry have to be studied. Commercially available shredders 

include the Swamp Devil (Aquarius Systems; http://www.aquarius-systems.com) and the 

Cookie Cutter. The Cookie Cutter is effective for destruction of extremely dense stands 

of wetland or emergent vegetation. It is a barge with two hydraulically driven knifelike 

blades, which spin rapidly, shredding a three-foot swath of vegetation in its path, and 

even grinding through soft sediments. It may create access and available habitat for 

shorebird nesting, but may also aid seed and fragment dispersal (U.S. Army Corps of 

Engineers 2001). Additionally, a prototype shredder designed for water hyacinth control 

(the Terminator; http://www.aquasolutionsusa.com/) can be hired for large projects. In 

Vermont, a shredding approach was conducted to control waterchestnut (Trapa natans 

L.) and generally killed the plants without adversely affecting water chemistry or causing 

nutrient problems (Ann Bove, pers. comm.). The effects of shredding on water quality in 

Delta water hyacinth stands is being evaluated by the APMP (NCAP Annual Report 

2003, Greenfield et al 2003). 

As with mechanical harvesting, mechanical cutting should not be conducted in 

circumstances where infestations are likely to spread. This includes fast moving waters, 

in addition to early infestations of species that spread by fragmentation. When shredding 

machines are used on species that spread by fragmentation (e.g., Egeria densa, Eurasian 

watermilfoil, hydrilla), there is substantial risk that the shredded material will spread to 

other locations and actually increase infestation. Therefore, mechanical shredding 

without removal is generally more appropriate for species that do not always spread by 

fragmentation, such as water hyacinth. In closed water bodies with complete weed 

coverage, shredding may be useful on any aquatic species for controlling plant biomass 

and achieving boat access (Madsen 1997; John Madsen, pers. comm.). 
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As with mechanical harvesting, effects to other aquatic organisms should be 

considered. Most literature to date has focused on effects of mechanical harvesting, with 

little evaluation of effects on ecosystems where cut plants were not removed from the 

water body. A mechanical shredding study found no significant difference in 

macroinvertebrate benthic community density, diversity, or richness after shredding of 

waterchestnut in a Vermont lake (Fiske 1999). Further research is warranted on the 

effects of cutting operations to animal populations. 

In California, mechanical cutting is frequently performed by resorts, marinas, and 

other relatively small lakeshore recreation managers to maintain access to their site. An 

example is the Soda Bay resort of Clear Lake, which performed cutting weekly from June 

15th through September 29th 1999. The resort had cutting equipment that attached to a 

boat and cut to a depth of five feet. After cutting, the fragments were removed from the 

water with rakes and pitchforks, distributed for composting at another privately owned 

location, and used for garden mulch (Lake County, Water Resource Division 1999). This 

use of low-tech, relatively inexpensive, but labor-intensive methods, is typical of 

mechanical cutting operations conducted by lakeshore commercial enterprises. 

Many agencies and companies build their own mechanical cutting boats for plant 

management in local ponds and canals. For example, Environmental Waterworks, an 

Orange County contractor, has built and operates a mechanical cutter that is operated on a 

boat 20’ long, 5’ wide, and weighing 600 pounds (Steve Walters, pers. comm.). Solano 

Irrigation District also constructed its own mechanical cutter, which it uses for weed 

control in selected irrigation ponds. Small boat operated cutters are appropriate for 

isolated small ponds such as those found in golf courses, where cut materials can be 

pushed to the banks and removed manually. Specialized underwater weed cutters can also 

cut weeds in water as shallow as ten inches and as deep as five feet. 

Mechanical cutting by hand held brush cutters has also been used experimentally 

on Spartina alterniflora in a Washington state bay. Cutting with herbicide application 

was more effective than cutting or application alone. This method reduced stem density 

and stem height when measured at the one-year post treatment mark but did not eradicate 

the plant (Major et al. 2003). Spartina alterniflora is threatening the native Spartina 
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species in the marshes in and around San Francisco Bay, and integrated approaches, such 

as mechanical cutting with herbicide applications, are currently in development for its 

control (ISP 2003). Mechanical cutting was also utilized on the nuisance weed 

waterchestnut (Trapa natans L.) in lakes in New York state. Cutting experiments 

reduced seed production, though some seeds were still produced (Madsen 1990; Methe et 

al. 1993). 

With the exception of specialty shredders like the Terminator, Swamp Devil, and 

Cookie Cutter, manual cutting is relatively inexpensive. Portable boat-mounted cutting 

units cost from $400 to $3,000. Specialized underwater cutters cost about $11,000. These 

tools are commercially available but can also be constructed in homemade fashion. Since 

no expertise is needed to operate these tools, costs can be limited to the purchase of 

cutting implements. Disposal fees may apply (Washington State Department of Ecology 

2001). 

Rotovation, Rototilling and Hydroraking 

Rotovation and rototilling are methods for chopping up and disturbing plants, 

focusing on the base of the plant, including submerged portions. A rotovator is a bargemounted rototilling machine that lowers a tiller head about eight to ten inches into the 

sediment to dislodge plant root crowns. Whereas rototilling could only be used with 

emergent vegetation, rotovation can also be used to control submerged vegetation. Unlike 

harvesters, rotovators do not have the capability to collect the uprooted plant material and 

the buoyant root masses float to the surface. The plant material may then be removed by 

a harvester following the rotovator, manually collecting plant material from the water 

surface, or raking along the beaches. However, the risk of spreading the infestation due to 

a large number of plant fragments is still high. Since the entire plant is removed from the 

sediment, rotovation can often reduce plant biomass throughout the growing season, 

sometimes even for two seasons (Gibbons et al. 1987). 

Water bodies suitable for rotovation include larger lakes or rivers with sufficient 

depth. Rotovation may not be appropriate in salmon-bearing waters, since it causes 

increased short-term turbidity. Additional risks include the potential impact of 

contaminants released from the sediment as well as the resuspension of various nutrients 
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to the water body. Rototilling can be used for control of emergent wetland vegetation, 

such as Spartina, cattails, and bulrush.

A rotovation attachment is available as part of the Aquamog mechanical system. 

The Aquamog has an excavator arm which accepts a number of different attachments. 

The rotovation attachment for the Aquamog is 10' wide, weighs about 2,000 pounds, and 

has 4 rows of spring steel tines that are off-set to increase efficiency at dislodging aquatic 

plants (BBMWD 2003). 

In Washington, the Willapa National Wildlife Refuge uses rototilling, in 

combination with targeted chemical spraying to control invasive Spartina alterniflora.

Spraying during low tide with rototilling during the winter appears to work well 

(Jonathan Bates, pers. comm.). Oregon has used rotovation to control Eurasian 

watermilfoil (Sytsma and Parker 1999). Winter tilling to a sediment depth of 4-6 inches 

reduced stem density by 80 – 90% for 2 to 3 years of control. 

As with mechanical harvesting, the risk of spreading viable plant fragments must 

be considered for rotovation and rototilling. For example, when Spartina stands are 

rototilled, viable rhizomes may be released and wash out to other areas with tidal 

movement (Vanessa Howard, pers. comm.). The potential for spread of viable Spartina 

fragments to new locations has not been studied for locations such as San Francisco Bay.

Hydroraking is a similar method to rotovation. In hydroraking, a heavy-duty 

metal rake is attached to a hydraulic arm, and then dragged across the lake bottom to 

dislodge buried plant material. As with rotovation, management considerations include 

disposal, and the potential for spreading of plant fragments, turbidity, and disturbance to 

bottom habitat (Holdren et al. 2001; Ann Bove, pers. comm.). 

Costs for rototilling, rotovation, and hydroraking vary according to treatment 

scale, density of plants, machinery used, and other site constraints. Contract costs for 

rotovation range from $1,200 – $1,700 per acre. Disposal fees may also apply (Taylor 

and Gately 1998). 
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Weed Rollers and Sweepers 

Weed rollers and sweepers are relatively new methods to control nuisance weed 

infestations in small locations. Weed rollers include a long metal cylinder (up to 30’) 

attached to a dock or piling on one end. A motor drives the cylinder forward and 

backwards in a 270-degree arc from the attachment point. The cylinder compresses 

young plants and soil in the area. Fin-like blades on the roller remove taller plants from 

sediment and may remove roots. For weed control, use once per week should be 

sufficient (Washington State Department of Ecology 2001). 

The use of rollers may disturb bottom dwelling organisms and spawning fish. 

Plant fragmentation of nuisance weeds may also occur (Washington State Department of 

Ecology 2001). Furthermore, in soft bottom areas, sediment disturbance can be 

significant (Terry McNabb, pers. comm.). Concern has also been expressed about the use 

of weed rollers on sediments high in organic matter. The Minnesota Department of 

Natural Resources regulates management of aquatic vegetation and requires permits for 

the use of weed rollers to protect littoral habitats (Minnesota Department of Natural 

Resources 2004). 

The Lake Sweeper is an automatic weed control device that may be used in 

similar areas to the weed roller. Like weed rollers, the Lake Sweeper is attached at one 

end to a dock or other fixed location and consists of a 24’ – 42’ metal pole that moves 

forward and reverse in a 270-degree arc. A pump provides the force to move the floating 

pole back and forth. Instead of rolling along the sediment, the Lake Sweeper floats along 

the lake surface, with a series of lightweight rakes dragging behind it. According to the 

manufacturer, these rakes can kill a variety of submerged aquatic plants within 3 to 5 

days by gradually weakening the plants. The Lake Sweeper may be an economically 

viable management option for small, high use locations. Purchase cost for a Lake 

Sweeper is approximately $2,000. Installation is said to be simple and operating costs are 

reported by the manufacturer to be very low (Kretsch 2003). Contact information for the 

manufacturer (Lake Restoration, Inc.) is available in Appendix A. The potential for the 

Lake Sweeper to increase rate of release of viable plant fragments has not been 

independently evaluated. 
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Diver-operated Suction Dredging 

Diver dredging is a mechanical control technology for plant removal, in which 

divers use pump systems to suction plants and roots from the sediment. The pumps are 

mounted on barges or pontoon boats and the diver uses a long hose with a cutter head to 

remove the plants. The plants are vacuumed through the hose to the support vessel where 

plants are retained in a basket and sediment and water are discharged to the water body. 

A silt curtain can be deployed to the treatment site to control turbidity (Washington State 

Department of Ecology 2001). 

The cost of diver dredging can vary depending on density of plants, type of 

equipment used, and disposal requirements. Nevertheless, it is typically a costly control 

option. State regulations on contract divers for dredging work are stringent and prevailing 

wage rates are high. Two divers and a tender are needed. Costs can range from a 

minimum of $1,100 per day to upwards of $2,000 per day with actual removal rates 

varying from approximately 1⁄4 to one acre per day (Taylor 1998). 

Considered a selective technique, driver dredging is particularly well suited for 

low-level, early infestations of noxious weeds. It can also be used to assist in long-term 

maintenance following herbicide treatments. Diver dredging is not recommended for 

control of aquatic beneficial plants (WDFW 1997). It has shown success in controlling 

noxious species, such as Eurasian watermilfoil. For example, suction dredging increased 

the number of native plant species one year after dredging and reduced the biomass of 

Eurasian watermilfoil in an oligotrophic lake (Boylen et al. 1996). 

Sediment Removal 

Sediment dredging has been used to remove nutrient rich sediment from irrigation 

canals. Plant propagules can also be removed when large amounts of sediment are 

dredged. Increased turbidity and suspended sediments can occur with this method. In a 

field study, plant biomass had a patchy distribution in areas where sediment was dredged 

compared to control sites (Sytsma and Parker 1999). 

Shading and Piping 

Shading may reduce plant/algal growth by limiting the amount of 

photosynthetically available light. Shading can be established by shade fabrics, canal 
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bank vegetation, or piping (putting irrigation underground) for irrigation systems (Sytsma 

and Parker 1999). Piping and shading can also reduce water loss due to evaporation. 

High storm water runoff and extensive maintenance requirements can be problems 

associated with these methods. Aquashade, a chemical product added to waters to reduce 

light penetration, is another shading method; it is discussed in the “Non-Conventional 

Chemicals” section of this review. Shading is also one of the mechanisms of control for 

bottom barriers, described below. 

Experimental studies have evaluated shading as a control method with varying 

degrees of success. Field experiments in English drainage channels showed that low 

shade (white geotextile material with 38% PAR reduction) and high shade (black 

geotextile material with 92% PAR reduction) had no significant effect on curly pondweed 

(Potamogeton crispus L.) biomass (Sabbatini and Murphey 1996). Filizadeh and 

Murphey (2002) provided evidence that shading may be effectively combined into 

integrated methods. In this study, shading combined with application of the herbicide, 

diquat, significantly reduced biomass of Sago pondweed (Potamogeton pectinatus L.). 

The combination of cutting, shading and diquat had better control on plant biomass than 

any of the methods tested individually (Filizadeh and Murphy 2002). Pondweeds are 

distributed throughout California, including the Bay region and Central Valley 

(DiTomaso and Healy 2003). 

For irrigation delivery canals, replacement of the canal by piping is an effective, 

long-term shading option. Pipes up to 36 inches in diameter can be readily installed in 

existing canal beds, and are likely to be able to transport 15 to 20 cfs. Pipes also provide 

for significant water conservation by eliminating seepage and evaporative losses. 

However, pipes are very costly to install, and not always appropriate for control of storm 

water flows (Sytsma and Parker 1999). 

Bottom Barriers 

Bottom barriers are semi-permanent materials that are laid over the top of the 

plant beds. They are analogous to using landscape fabric to suppress the growth of weeds 

in yards. By eliminating the sunlight from the area, bottom barriers interfere with 

photosynthesis, causing covered plants to die. 
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Although bottom barriers may kill and remove plants originally present, once the 

barriers are removed, the nuisance species often rapidly recolonizes. This has frequently 

been observed for Eurasian watermilfoil. In one study, Eurasian watermilfoil re-colonized 

44% of grid squares within 30 days of benthic barrier removal (Boylen et al. 1996). In 

Lake George, New York, and in a Wisconsin study, Eurasian watermilfoil rapidly recolonized sites after barriers were removed, indicating a continuing need for control after 

removal (Eichler et al. 1995; Helsel et al. 1996). 

Bottom barriers have had some success in lakes in Wisconsin, New York, and 

Washington, but were not reported successful in Clear Lake, California. In Lake George, 

New York, no plants remained after use of a PVC barrier (the PalcoTM barrier), but there 

were plants under mesh screen (AquascreenTM) barriers (Eichler et al. 1995). In 

Wisconsin, PalcoTM liners completely eliminated all plants under the barrier (Helsel et al. 

1996). In a 700-acre Seattle-area reservoir, bottom barriers were used to control a new 

infestation of milfoil plants. In this system, the bottom barriers were part of a successful 

eradication program that did not use herbicides (Zisette 2001). 

In California waters, bottom barriers are being used in a variety of management 

circumstances, including some integrated control and innovative methods. The Invasive 

Spartina Project is conducting experimental evaluations of bottom barriers constructed of 

biodegradable fiber cloth for control of new Spartina infestations. Use of these 

biodegradable materials reduces the possibility that bottom barrier material will pollute 

the ecosystem, because barriers can be difficult to retrieve (Erik Grijolva, pers. comm.). 

In offshore waters of the southern California coast, bottom barriers are currently part of 

an integrated program to eradicate the noxious algae, Caulerpa taxifolia. In this program, 

plants are covered with vinyl containment tarps, and solid chlorine pucks are placed 

under the barriers. This combination of chemical and non-chemical stressors has been 

successful in eradicating this hardy species (Bill Paznokas, pers. comm.). Bottom barrier 

pilots in Clear Lake have been less successful. Bottom mats, installed at a Clear Lake 

resort, had sediments and vegetation growing on top of them within a year, and the area 

had to be mechanically harvested (Lake County Water Resource Division 1999). 
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Bottom barriers are more difficult to install in water bodies where currents or 

strong tides occur. The installed fabric can loosen, float to the surface, and cause danger 

to boat traffic or swimmers. Because of this, bottom barriers may be difficult to maintain 

in tidally influenced areas of the Sacramento-San Joaquin River Delta, estuarine areas, 

and coastal areas. 

Bottom barriers will result in the loss of habitat for benthic organisms due to the 

loss of the bottom vegetation. A physical and chemical evaluation of sediment conditions 

under synthetic fabric barriers showed that invertebrate density declined up to 90%. 

Benthic barriers apparently blocked sedimentation and caused an increase in NH4 and a 

decline in dissolved oxygen to near zero beneath the fabric. Community effects were 

reported to be more severe in warm water. However, biotic conditions recovered quickly 

after barriers had been removed (Ussery et al. 1997). Nevertheless, the impact would be 

limited to the area where bottom barriers are applied, and would be unlikely to have 

widespread impact on a large water body. 

Bottom barrier material costs vary depending on the type of material used. Costs 

can range from $0.1 – $0.6 per square foot; costs for professional installation are an 

additional $0.25 - $.50 per square foot. Bottom barriers are generally not a cost effective 

method to control infestations covering large surface areas. They are appropriate to 

control growth in specific areas, such as adjacent to marinas and docks. 

Bottom barriers and covers may be used for irrigation canals. Lining irrigation 

canals with concrete or geotextile material can reduce the substrate available for plants to 

root (Sytsma and Parker 1999). Sediment deposition may reduce the long-term 

effectiveness of this procedure. 

Manual Removal 

Many programs involve manual removal of plants from the lake bottom. 

Typically, care is taken to remove the entire root crown and to not create fragments. In 

deeper waters, divers are often needed to reach the plants. Depending on visibility in the 

water, sediment type, and restriction on plant fragmentation, manual eradication methods 

may not be suitable for certain water bodies. 
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Hand removal has several advantages and disadvantages over more sophisticated 

methods of aquatic weed control. In shallow waters, or with floating plants, it requires 

little skill or equipment to manually remove aquatic plants. Therefore, the method can be 

employed by volunteers, untrained workers, or inmates, and large capital expenses are 

not required. With proper training, the method can be employed to selectively remove 

specific weeds, while limiting disturbance to desirable plants. The disadvantage to hand 

removal is that it is slow and labor intensive, and is therefore not generally appropriate 

for controlling large or dense infestations or eradicating plants with extremely rapid 

growth. One example of a manual removal effort that failed was a multi-agency pilot 

effort to control giant salvinia (Salvinia molesta) in the lower Colorado River. In this 

project, several dozen volunteers from various agencies used nets to scoop out many tons 

of salvinia. Because of the inability to remove all plant material, the great abundance of 

remaining plant material, and the extremely rapid vegetative regrowth, the project was 

considered a complete failure and was discontinued (Laura Crum, pers. comm.). In 

general, the method will prove most successful with early infestations or to maintain 

control in limited areas. 

A hand-pulling program has been established for hydrilla control in several 

California water bodies. For example, in the Yuba canal, one CDFA Associate Biologist 

has been spending approximately five full months per year conducting hand removal of 

approximately 30,000-40,000 individual hydrilla plants. Plants were disposed of by 

drying and placing in a closed container in the trash. In the Yuba canal, the hand removal 

was conducted in combination with application of the copper herbicide KomeenTM to the 

water column. This integrated pest control method was reasonably effective at reducing 

hydrilla growth, resulting in a statistically significant reduction in tuber density over the 

sampling years (Ross O’Connell, pers. comm.). 

A number of California agencies have expressed interest in conducting hand 

removal programs but have reported a surprising degree of difficulty with permitting 

issues. The CDBW intends to implement a hand-pulling program for water hyacinth in 

the Delta to augment current chemical control efforts. In this program, plants would be 

disposed of cost-effectively, by placing them along levee banks (USDA and CDBW 

2003). This program has had difficulty obtaining the necessary permits for 
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implementation. It did receive approval from USFWS and NOAA-NMFS, but has been 

hindered by difficulty obtaining NEPA and CEQA approval from the Regional Water 

Quality Control Board. Approval has been hindered by the concern that hand removal 

efforts may stir up the water body, creating a discharge of nutrients from the disturbed 

plants. Additionally, it was determined that landowner approval must be obtained to 

dispose of removed material on any levee banks (Cynthia Gause, pers. comm.). 

According to the 1994 Integrated Aquatic Vegetation Management Plan Manual, 

hand-pulling expenses can run between $500 and $2,400 per day (Gibbons et al. 1994). 

As with diver dredging, removal rates for hand pulling depend on plant density, visibility, 

and sediment characteristics. Use of volunteer labor could considerably reduce costs. 

Some volunteer manual removal programs are quite sophisticated. For example, to 

control Eurasian watermilfoil in Lulu Lake, Wisconsin, volunteer divers with The Nature 

Conservancy clip individual plants at the base, and volunteer canoers collect and remove 

the resulting fragments (Hannah Spaul, pers. comm.). 

Water Level Manipulation 

Aquatic weeds can sometimes be effectively controlled by dewatering water 

bodies. This may involve pumping or releasing water via a dam or weir. Drawdown is 

frequently used in wildlife refuges by federal or state wildlife agencies or local duck 

clubs. For example, three months of drawdown can control emergent wetland vegetation 

(cattails and bulrush) at the Kern National Wildlife Refuge in California (Dave Hardt, 

pers. comm.). It is also viable in some man-made reservoirs and irrigation canals. 

Nevertheless, many water bodies lack the water level control structures needed to achieve 

significant plant control (Washington State Department of Ecology 2001). 

Water drawdown can have variable impacts on water quality and aquatic plant 

survival. Water drawdown may increase phosphorus release from the sediment upon 

rewetting (Klotz and Linn 2001). Alternatively, phosphorus loading may decrease by 

increasing benthic oxygen levels, which favors sequestering of phosphorus in the 

sediment (Coops and Hosper 2002). If there is sufficient water flushing, drawdown can 

reduce water column nutrient concentrations and algae growth (Holdren et al. 2001). 

However, drawdown can have varying impacts on different rooted plant species, with 
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some nuisance species not harmed by the manipulation. In fact, aquatic plant biomass can 

even increase after drawdown (Wagner and Falter 2002). The impacts of drawdown to 

flora and fauna are severe and this method should only be applied to water bodies where 

short-term habitat impacts are acceptable to resource agencies. 

In systems where water levels may be readily controlled, water level manipulation 

may be used to control the timing of aquatic plant infestation growth. For example, in 

irrigation drainage systems, it may be possible to add water prior to the irrigation season, 

allow aquatic plants to grow, and then remove the water to kill the plants. This method 

may reduce the capacity for plant growth during the irrigation season by reducing the 

pool of available nutrients (Lars Anderson, pers. comm.). 

If a water level structure is in place, costs may be minimal (Washington State 

Department of Ecology 2001). In some cases, natural fluctuations in water levels 

resulting from drought can result in substantial die-off of invasive aquatic plants (Gene 

Martin, pers. comm.). 

Channel Clearing or Excavation 

In some cases, it may be cost-effective to remove plant and surface sediment 

material from a water-body. This may be achieved by a mechanical excavator or by 

flushing material downstream of a given site. It may also be achieved by chaining, in 

which a chain is dragged along the channel bottom between two heavy-duty vehicles. 

Removal of plants and sediments may also reduce future growth by reducing the 

abundance of seeds and the pool of available nutrients. 

These methods are more appropriate for storm water or irrigation canals, because 

the water level may be relatively low, access to the entire water surface is relatively easy, 

and the habitat value is not considered to be important. There is the potential for 

increased turbidity downstream of the target site, and disposal of removed material may 

be an issue. Often times, these methods are easier in systems having a hard-bottomed 

substrate or a concrete base. 

Excavation is a method commonly used throughout California for management of 

irrigation canals and other small waterways. The Los Banos Wildlife Area (managed by 

CDFG) uses it for control of water hyacinth and water primrose in some of their 
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irrigation canals (Bill Cook, pers. comm.). Mechanical excavation is also used on a 

limited basis at the Merced and Solano Irrigation Districts. These districts use excavators 

to remove sediment, overlying vegetation, and perennial below ground structures. They 

prefer to use chemical control, finding it more cost-effective in most channels, but use 

excavation in channels where there is a risk of chemical release into tightly regulated 

natural waters. The Solano Irrigation District channel is concrete lined, making it 

possible to remove most of the sediment, thereby limiting plant growth (Bob Acker, pers. 

comm.; Mark Vale, pers. comm.). 

The Richvale Irrigation District relies on mechanical excavation for aquatic plant 

control in both main and lateral irrigation canals. They switched to mechanical methods 

20 years ago, to avoid permitting issues, recreational concerns, and inadvertent fish kills 

in the public recreation area downstream of the irrigation canals. A single excavator 

operator can clear about one mile of ditch per day and the plant removal is reported to be 

very effective. Regrowth with this method is slow; typically, a single site requires 

excavation only once every one to three years. Spoils are stacked along the edge of the 

canals, and either used to maintain the adjacent roads or transferred to the canal edge to 

reduce erosion. The system is relatively easy to apply in this region, because the channel 

bed is composed of hardpan (extremely compacted clay), but it is appropriate (and used) 

for irrigation canals in other regions. Several other agencies subcontract with the 

Richvale Irrigation District, to have their channels excavated, at the cost of $75/hour 

(Troy Kellet, pers. comm.). 

Sediment excavation may also be used in lake restoration, though the expense of 

the method is significant and success rate varies among water bodies. Sediment 

excavation has been used in a New York lake to remove thick organic sediment and an 

infestation of curly pondweed (Potamogeton crispus L.) from the lakebed (Tobiessen et 

al. 1992). Dredging the sediment bed with a Mudcat Model MC-10 hydraulic dredge 

resulted in a sustained (ten year) decrease in biomass of pondweed at the dredged sites. 

Dredging may reduce light availability to bottom dwelling plants by increasing the depth 

of the water column. Sediment dredging was not successful at a highly eutrophic lake in 

Sweden (Annadotter et al. 1999). Despite removal of 25% of the sediment area, 

phosphorous was still being released to the water column. 
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Exposure of Plants to Extreme Environmental Conditions (Heat, Steam, Flame, 

Cold, or Electricity) 

In theory, aquatic plant survival and growth may be inhibited by subjecting the 

plants to extreme environmental conditions. Steam applications, exposure to heated 

water, flame, or freezing conditions could all kill vascular plants. In dewatered areas, 

high voltage electricity could be used to kill plants. In practice, these methods have 

received little study or evaluation for field application. The limited studies of these 

methods do indicate promising results (reviewed in Sytsma and Parker 1999). For 

example watermilfoil fragments exposed to heated water for ten minutes were severely 

reduced. A New Zealand-based company (Waipuna; www.waipuna.com) has developed a 

commercially available system, which sprays heated water directly on plants and then 

covers it with an organic foam surfactant, which traps the heat and kills the plants. The 

method would be appropriate for vegetation control in riparian or dewatered areas; in 

some management circumstances, it is comparable in cost and effectiveness to glyphosate 

applications (Quarles 2001). 

Gourd and Ferrell (2003a, b, c) evaluated use of propane flame treatment and 

steam spraying using commercially available equipment for weed control. In their 

studies, two early season applications with a butane flamer generally controlled perennial 

weeds in irrigation canals and ditch banks. In contrast to flaming, steam spraying did not 

achieve adequate control in the work of Gourd and Ferrell (2003a). Although flaming 

appeared to be more effective than steaming, it could only be used in locations having 

low wildfire risks, and where permitted by air pollution laws. 

Another potential alternative control method is application of extremely cold 

material to aquatic plants. Liquid nitrogen or liquid helium could be sprayed directly onto 

exposed portions of floating or emergent plants. This method has never been attempted 

(Jeffrey Stuart, pers. comm.). In dewatered areas, plants could also be subjected to high 

voltage electricity. The human health risks of both these methods would be considerable 

(Lars Anderson, pers. comm.). 

Aeration, Oxygenation, and Water Circulation 

In water bodies where excess growth of nuisance algae is a concern, water quality 

can often be improved by physically mixing the water (circulation), or interspersing the 
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water with surface air (aeration) or pure oxygen (oxygenation). When applied correctly, 

these methods can help maintain oxygen levels throughout the water body, and reduce 

algae production (Holdren et al. 2001). 

Aeration, oxygenation, and water circulation can all help maintain oxygen levels 

in the hypolimnion, which ultimately reduces algae growth by reducing the rate of 

nutrient recycling into the water. Thermal stratification can create a barrier to full mixing 

of the water column, resulting in a hypolimnion that is anoxic. Nuisance phytoplankton 

blooms can occur in the epilimnion of aquatic systems as long as there are ample 

nutrients and light available. This is particularly a problem in aquatic systems that have 

excess nutrients. Anoxia in the hypolimnion and the sediment-water interface can 

enhance the release of phosphorus and nitrogen from the sediment into the water column. 

Eventual mixing will bring these nutrients into the photic zone where they stimulate 

primary production (Horne and Goldman 1994). When used effectively, aeration, 

oxygenation, or water circulation control the release of nutrients from the lake bottom, 

thereby reducing algal growth and consequent reliance on direct herbicide application. 

Many municipal water districts and waste treatment operations in California 

currently use aeration and circulation to reduce production of algae and foul taste and 

odor producing compounds. For example, Marin Municipal Water District has several 

aerators established in their reservoirs to maintain water circulation (Larry Grabow, pers. 

comm.). 

In aeration, water-air surface exchange is increased by mechanical means, which 

can increase oxygen content of low-oxygen waters (Fast and Boyd 1992). In 

oxygenation, pure oxygen is injected directly into the water. The advantages of 

oxygenation to the hypolimnion (vs. aeration) are 1) maintenance of thermal stratification 

and a cold-water environment for fish habitat 2) an increased solubility of oxygen in 

water over air 3) an increased transfer efficiency and 4) avoidance of excess nitrogen in 

the water column (Beutal and Horne 1999). Methods of oxygenation include side stream 

pumping systems, deep oxygen injection systems, and submerged contact champer 

systems. All three systems have been able to increase dissolved oxygen concentrations in 
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water, and some can reduce internal loading of nutrients from sediment to the water 

column. 

There are two primary types of aerators, ‘splashers’ that aerate by dispersing 

water through air, and ‘bubblers’ that aerate by dispersing air through water (Fast and 

Boyd 1992). These devices can be run electrically or by solar power. The Solar-Bee

aerator uses solar energy to pump water from depth and disperse it over the surface. 

Initial cost of the Solar-Bee is higher than non-solar aerators, but the energy savings 

over the long term may make Solar Bee systems cost-effective. 

Some California agencies report using physical pumping or recirculation of water 

as a method to control production of nuisance algae. The Tahoe Keys Property Owners 

Association has established a series of water circulation pumps to control the algae 

problem (Greg Tischler, pers. comm.). The manager of Alameda Lagoon has also 

reported success with water aeration units, for breaking up algal mats (Tom Jordan, pers. 

comm.). For very small water bodies, practitioners have even reported using a spray 

pump and fire hose system to break up and sink algal mats (Tom McNabb, pers. comm.). 

The method may interfere with algal growth via water disturbance and movement of the 

algae to portions of the water column that inhibit development (e.g., areas with reduced 

light availability). Recirculation may also be achieved by installation of water pumps or 

fountains. 

Studies of Aeration in Aquatic Systems 

Hypolimnetic aeration may be useful in lakes that have internal loading of 

nutrients from bottom sediments to the photic zone. A number of peer-reviewed research 

studies suggest that hypolimnetic aeration may be an effective method of controlling 

algal growth and related chemical parameters. Prepas and Burke (1997) studied 

hypolimnetic oxygenation of a deep eutrophic lake in central Alberta over a six-year 

period. The hypolimnetic oxygenation resulted in reduction of phosphorus release from 

sediments, hypolimnetic reductions in ammonia, increased oxygen levels in the 

hypolimnion and an increase in nitrate + nitrite in the hypolimnion. Concentrations of 

total phosphorous, inorganic nitrogen, and chlorophyll-a all decreased in the epilimnion 

during the summer months. Continual aeration was necessary to maintain these 
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conditions. The cost of the project was $30,000 capital costs and $49,000/year for 

aeration. 

Cowell et al. (1987) studied full lake aeration in a small sinkhole lake in Florida. 

The aeration completely eliminated thermal stratification in the warm months. Dissolved 

oxygen of the bottom waters increased significantly and turbidity, pH, alkalinity, total 

nitrogen, hydrogen sulfide, and iron decreased significantly. Although there were 

decreases in many of the nutrients, and a decrease in blue-green algae, neither primary 

production nor chlorophyll-a concentrations changed significantly. The authors 

concluded that continued aeration over a few years may be necessary to reduce primary 

production. 

Aeration was not successful in removing total ammonia nitrogen from waters 

under laboratory conditions (Chiayvareesajja and Boyd 1993). In aquaculture ponds, 

aeration increased dissolved oxygen in bottom waters and reduced soluble reactive 

phosphorus but increased total phosphorus due to re-suspension of phosphorous from the 

sediment (Masuda and Boyd 1994). 

In addition to altering nutrient flux from sediment to the water column, aeration 

may also aid in fish growth and reproduction. In an aerated eutrophic Florida lake, total 

catch/hour increased by 50% over a non-aerated period of the same lake (Leslie et al. 

1986). The aeration system was able to completely turn over the 10.5-hectare lake every 

7 – 11 days. Costs, including capital costs, were $436/month for the two-year aeration 

period. 

Nutrient Removal 

In lakes or impoundments with a high degree of nutrient recycling from the 

bottom sediments, it may be possible to remove nutrient-rich waters or sediment directly 

from the bottom of the lake. This method is uncommon, and requires a good 

understanding of the chemistry and nutrient budget of the lake. Removal of nutrient-rich 

water appears to be working in Devil’s Lake, an important recreational lake in southern 

Wisconsin (Richard Lathrop, pers. comm.). Devil’s lake is characterized by water very 

rich in phosphorus in the deepest portion of the lake, resulting from historic loads of 

phosphorus. Natural resource managers with the Wisconsin Department of Natural 
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Resources have set up a 20-inch diameter siphon pipe running from the deepest portion of 

the lake out to an intermittent stream channel. To maintain the lake-level, water is 

pumped from a nearby stream, low in nutrients. Because the water nutrient concentration 

is highest at the lake bottom, the expectation is that withdrawal of this phosphorus rich 

water should limit nutrient loading and resulting algal blooms over the next 15 years. The 

project is also expected to reduce incidence of swimmer’s itch and mercury 

concentrations in sport fish, as indirect results of the reduced lake productivity 

(Wisconsin Department of Natural Resources 2001; Richard Lathrop, pers. comm.). 

NON-CONVENTIONAL CHEMICAL CONTROLS 

In addition to conventional herbicides and pesticides, there are other chemicals 

that can be utilized to reduce primary production in aquatic systems. These are typically 

used to control development of nuisance algal blooms. Nuisance algal blooms create 

unpleasant conditions in recreational water bodies and can create taste and odor problems 

in drinking water reservoirs. Although not well studied, alternative chemicals may also be 

used for control of benthic algae and floating and submerged vascular plants. The US 

EPA has so far only approved Aquashade for use in aquatic environments. The effects of 

many other non-conventional control methods are not well tested, particularly for use in 

the littoral zone and for control of rooted or free-floating vascular plants. 

Research has been conducted to study the effects of certain chemicals on the 

release of nutrients from anoxic sediments of eutrophic lakes. Eutrophic lakes can have 

internal source loading of nutrients from sediment to the water column, especially when 

the hypolimnion and porewater are anoxic. Primary production can be reduced by 

reducing nutrient concentrations in the photic zone. Under anoxic conditions, 

phosphorous, an important nutrient for algal/plant growth, is released from the sediment 

to the water column. Certain chemicals can be added to eutrophic lakes that can bind 

phosphorous and precipitate it out of the water column into the sediments where it stays 

sequestered as long as oxic conditions continue (Horne and Goldman 1994). Jaynes and 

Carpenter (1985) found that the roots of certain macrophyte species can release oxygen 

directly into the sediment, thereby changing the redox potential to favor sequestering of 

phosphorus in the sediment. However, the net flux of phosphorus into eutrophic systems 
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must be determined as senescence of macrophytes may also be a source of internal 

loading. 

These chemical applications have generally received little attention in California 

waters. Both rigorous scientific studies and field trials should be undertaken to evaluate 

the effectiveness of these methods in California lakes and reservoirs. Currently, the 

Marin Municipal Water District, funded by the Aquatic Pesticide Monitoring Program, is 

evaluating the effectiveness of gypsum and alum for control of benthic algae in one of 

their reservoirs. 

Calcium-based Products 

Calcium based products, including lime (Ca(OH)2), limestone (CaCO4), and 

gypsum (CaSO4) are frequently used for control of aquatic algae and submerged aquatic 

plants. Several studies have documented reduced plant growth as a result of lime 

application. Repeated treatments (over a seven year period) to hard water eutrophic lakes 

in Canada reduced photic zone phosphorous and chlorophyll-a concentrations and 

average macrophyte biomass was reduced (Prepas et al. 2001). Single applications of 

lime gave short-term (< 1 year) control of phosphorous and long-term control (>1 year) 

of submerged aquatic plants (Reedyk et al. 2001). 

Positive results have been observed in studies using iron gypsum (Fe-CaSO4 ). 

Iron gypsum was effective in reducing hypolimnic total phosphorus (TP) by 90% and 

increased water clarity (secchi depth reading) from 50 to 270 cm in a Finnish eutrophic 

lake. One year after application, TP was reduced by an average of 62% for the entire 

water column (Salonen et al. 2001). Iron gypsum also reduced methane production and 

release, reduced release of phosphorous from anoxic sediment, and improved redox 

conditions in laboratory experiments utilizing sediments from a eutrophic lake in Finland 

(Varjo et al. 2003). The reduction of methane production is important because methane 

released from sediments can transport nutrients into the photic zone. Iron is important in 

adsorbing phosphorous in the sediment. 

As compared to lime and iron-gypsum, limestone studies have had less positive 

results. Studies of limestone application in aquaculture ponds have shown mixed results 

in reduction of nutrients and algae production. In aquaculture ponds, limestone did not 
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reduce TP or soluble reactive phosphorous (SRP) concentrations compared to controls 

(Masuda and Boyd 1994). Application in catfish ponds did not reduce TP, chlorophyll-a 

concentrations, or cyanobacterial abundance but oxygen production did decrease (Giri 

and Boyd 2000). Limestone application was not effective in reducing phytoplankton 

densities. 

Aluminum based products 

Alum (Al2(SO4)3) is a salt that can precipitate phosphate out of the water column 

and sequester it in the sediment, thereby reducing phosphate availability to primary 

producers (Horne and Goldman 1994). In a French soft water eutrophic lake, SRP 

concentrations were reduced by alum, although alum was not added in sufficient amounts 

(due to potential aluminum toxicity) to reduce total phosphorus (Van Hullebusch et al. 

2002). Despite low SRP, a bloom of the noxious algae species (Microcystis sp.) 

appeared. In the lab utilizing sediments from shallow eutrophic Swedish lakes, 

aluminum treated sediments released less phosphorous than untreated sediment. If 

sediment conditions are anoxic the dosing of alum is dependent on the concentrations of 

Fe-P (phosphate adsorbed to iron) as oxidation of Fe-P will release phosphate from the 

sediments to the water column. (Rydin and Welch 1998). Alum reduced SRP and 

turbidity in aquaculture ponds (Masuda and Boyd 1994), though repeated applications 

were necessary. 

A 13-year follow-up study on a Vermont lake showed that one application of 

alum and sodium aluminate increased water quality. Summer photic zone total 

phosphorus and chlorophyll-a had decreased by 68% and 61%, respectively, since preapplication measurements. Weight loss occurred in large yellow perch for the first three 

years following application and the macroinvertebrate density decreased by 90% one year 

after treatment. The macroinvertebrate density recovered in all areas with some densities 

exceeding pre-treatment numbers (Smeltzer et al. 1999). Alum treatment was effective 

for a range of 8-11 years in polymictic lakes and a range of 13-20 years in dimictic lakes 

(Welch and Cooke 1999). 
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Nitrate 

Nitrate has also been utilized to reduce internal loading of phosphorous from 

sediments to the water column. Sondergaard et al. (2000) injected low doses of nitrate 

into the hypolimnion of a thermally stratified eutrophic lake. Hypolimnetic dissolved 

organic phosphorous was reduced by 23 – 52% during the treatment years. Dissolved 

nitrate was more effective than granulated nitrate. 

Many of the above chemicals are successful in sequestering nutrients in the 

sediment by precipitating nutrients out of the water column and sequestering them in the 

sediment. How these chemicals may affect aquatic and benthic organisms still needs to 

be addressed. For example, the iron in iron gypsum compounds can be harmful to 

animals. In lab studies of effects on zooplankton, particulate iron caused mortality and 

decreases in reproduction (Randall et al. 1999). 

Aquashade 

Aquashade is an EPA registered chemical that controls growth by filtering out 

photosynthetically available radiation (PAR) in the range of blue-violet and red-orange. 

Several contractors use Aquashade for control of algal growth in California waters. It is 

commonly used in recreational lakes and ponds, when homeowners are interested in 

reduced algae or aquatic plant growth. However, certain municipalities choose not to 

apply it because local stakeholders think it creates an unnatural appearance in the water 

body (Craig Crawford, Santa Clara County Department of Parks and Recreation, pers. 

comm.). In California, the Central Valley Regional Water Board has received a small 

number of applications to use Aquashade and calcium products for nuisance vegetation 

control. They did not instruct the applicants to seek an NPDES permit but are still 

awaiting guidance from the State Water Board on this issue (Emily Alejandrino, pers. 

comm.). 

The limited available experimental research suggests that Aquashade is an 

effective method of controlling aquatic algae. Lab experiments have shown that 

applications of Aquashade in varying concentrations reduce the transparency of the water 

and increase the light extinction coefficient (Kd) over control locations. Aquashade 

absorbs light in the spectrum of 550 – 650 nm (Madsen et al. 1999). In the lab, 
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application of Aquashade did not affect the oxygen uptake rates of the crayfish, 

Orconectes propinquus (Spencer 1984), suggesting that it is not toxic to crayfish. 

Additional research on how Aquashade affects plant/algal growth is necessary to see 

under what circumstances this method is successful. 

Salt (Sodium Chloride) 

Aquatic plants generally have limited salinity regimes in which they can survive, 

and exposure to saline conditions will kill hydrilla, Eurasian watermilfoil, and other 

freshwater plant species (Twilley and Barko 1990). Exposure of water bodies or 

dewatered areas to solid salts (sodium chloride) could potentially kill plant beds and 

inhibit future growth. However, addition of salt in large quantities would likely kill native 

plants and animals, along with introduced plants. 

We have identified two case studies of salt addition attempts for control of aquatic 

plants. The Mountain View Sanitary District, in California, added rock salt to mowed 

cattails that had experienced a natural dewatering event. The practitioners hypothesized 

that the combination of multiple stresses (recent mowing, drying, and salt addition) 

would kill the plants. But their experiment was hampered by difficulties in 

implementation, including insufficient penetration of treatment area, followed by 

flooding, which ultimately resulted in insufficient salinity for toxicity (Dick Bogaert, 

pers. comm.). The other case study is Capital Lake, in Washington State. The Washington 

Department of Ecology is currently considering controlling Eurasian watermilfoil in 

Capital Lake by reintroducing salt water (historically, it was a salt water lake), but there 

is concern that saltwater influx would damage the newly developing freshwater 

ecosystem (Condon 2003). In summary, the addition of salt probably has limited 

application for aquatic plant control.

NPDES Permitting Status of Non-Conventional Chemicals 

Alternative chemicals such as gypsum, lime, alum, acetic acid and Aquashade 

may be better received by the public than conventional target-specific pesticides. Also, in 

many cases, they are relatively inexpensive to purchase. However, as with barley straw, 

the permitting status of these chemicals is not clearly established. Calcium products, iron, 

and alum all reduce primary production by sequestering nutrients, rather than direct 
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mortality to aquatic plants. Because their mechanisms of action do not direct mortality to 

plants or algae, they are not herbicides, per se. Aquashade, as well, functions by reducing 

light penetration, and is not a direct herbicide. Acetic acid does act as a contact herbicide, 

and has not been permitted as such, so it may not be appropriate for use by public 

entities. 

In California, the Central Valley Regional Water Board has received a small 

number of applications to use Aquashade and calcium products for nuisance vegetation 

control. They did not instruct the applicants to seek an NPDES permit but are still 

awaiting guidance from the State Water Board on this issue (Emily Alejandrino, pers. 

comm.). 

PREVENTIVE MEASURES 

In addition to methods for removing nuisance plants, algae, or nutrients from 

water bodies, there are a variety of proactive methods to keep the infestation or algal 

bloom from occurring in the first place. Nutrient loading to water bodies can be curtailed 

by watershed management strategies. Nuisance species introductions can be limited by a 

variety of preventive measures. Extensive reviews have been developed elsewhere on the 

range of options available for both watershed management (e.g., Holdren et al. 2001; Lee 

and Jones-Lee 2002) and prevention of alien species invasion (e.g., Wittenberg and Cock 

2001; Madsen 1997). A brief summary of available preventive measures follows. 

Early Detection 

The spread of invasive species can be controlled by patrolling water bodies, 

detecting early infestations, and removing the invasives before they have a chance to 

spread (Madsen 1997; Wittenberg and Cock 2001). Early detection can reduce the 

environmental and economic costs associated with noxious weeds. For a given water 

body, fewer resources are needed to remove early infestations than widespread 

infestations. In many instances, the costs of early detection programs can be limited by 

enlisting volunteers from environmental non-profits. In coordination with local 

management agencies, The Nature Conservancy is setting up a volunteer early detection 

program to control the spread of Eurasian watermilfoil in Adirondack State Park 
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waterways in New York (The Nature Conservancy 2003; Hilary Oles, pers. comm.). 

States with active weed watcher programs include Minnesota, New Hampshire, and 

Vermont (Madsen 1997). 

Coordinated early detection programs have not been established to control 

infestations in California fresh waters, though such programs would be appropriate for a 

number of noxious weeds. California does have a border quarantine in effect for hydrilla 

(described below). The Department of Fish and Game is conducting visual and sonar 

inspections of high-risk areas for the marine invasive plant, Caulerpa taxifolia (Johnson 

2001). 

Quarantine and Regulation 

In some cases, the federal or state government can pass legislation controlling the 

spread or possession of nonindigenous species, including aquatic plants. The state of 

California has established a quarantine policy that restricts the importation of noxious 

species, including a number of aquatic invasive pests. State regulators are able to reject 

the import of shipments infested with viable fragments or seeds from hydrilla, Eurasian 

watermilfoil, water primrose, Salvinia species, and other aquatic and terrestrial weeds. 

These restrictions occur at the roadside agricultural inspection stations at the borders with 

other states. In the case of hydrilla, shipments of aquatic plants, such as vegetation in fish 

shipments, are also prohibited in entry from areas with large hydrilla infestations, unless 

accompanied by a certificate verifying that no hydrilla is present. Other species, including 

water hyacinth and water lettuce are restricted only from transition to locations where 

they are rare or currently being eradicated (CDFA 2003b), and the enforcement 

mechanism for these restrictions is not clear. 

In addition to quarantine, there are additional legal protections and enforcements 

that can be undertaken to restrict invasion of aquatic pests. For example, the State of 

Washington has a list of invasive aquatic plants that are banned from sale within the state. 

The Oregon State Department of Agriculture enforces these bans by inspecting nurseries 

and pet stores for the banned plants. Civil penalties can result from sale of these plants 

(Hamel and Parsons, 2001). 
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On the Internet, most invasive aquatic plants are readily available for purchase. A 

recent search of the internet found that twelve highly invasive plants were found listed for 

sale by wetland nurseries and water garden dealerships throughout the U.S. and 

internationally. This finding indicates a clear need to improve development and 

enforcement of laws needed to prevent further introduction of noxious weeds from 

commercial sale (Kay and Hoyle 1991). 

Education and Outreach 

For many noxious weeds, educational information can be provided to water body 

users, to help reduce the probability of unintentional introductions. This information 

could be provided in the form of brochures, web sites, and posters. Additionally, signs 

can be posted at water body boat launches, bait shops, or nurseries where aquatic plants 

are sold, identifying nuisance species likely to be inadvertently introduced. The 

expectation is that once people are educated about the problem plants and how they 

spread, people will be less likely to put them in natural waters. To achieve this, 

educational materials often discourage disposal of nuisance species in or near natural 

waters, transfer of nuisance species between waterways (e.g., on boat hulls or trailers), or 

intentional release of nuisance species into the wild. 

Riparian Buffer Strips 

Buffer strips alongside waterways can impede the inflow of effluents, thereby 

reducing eutrophication. Planting native perennial species at the perimeter of water 

bodies may aid in the absorption of nutrients. This may also help reduce soil erosion 

(Lembi, 2003). In Gainesville, Florida, a non-profit organization (Adopt-A-River) works 

closely with local wetland biologists and municipal employees to plant riparian buffer 

strips on a city creek. To control costs, they populated the strips with native plants dug up 

from storm water ditches from other locations (Fritzi Olson, pers. comm.). In southern 

Wisconsin, The Nature Conservancy has extensive planting programs for native prairie 

and savannah grassland species. These programs are undertaken to achieve the duel 

benefits of conserving native grass species and improving the water quality of nearby 

lakes and rivers (Hannah Spaul, pers. comm.). Riparian buffer strips are also used to 

control storm water phosphorus loading from residential developments (e.g., Woodard 

and Rock 1995). As with many watershed management techniques, the cost-effectiveness 
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of buffer strips for controlling bioavailable nutrient loading has not been systematically 

evaluated for California waterways (Lee and Jones-Lee 2002). 

Retention Pond or Wetland Construction 

Establishing a settling or retention pond or a wetland at effluent sources can allow 

nutrients to settle or be processed before they reach water bodies. Retention ponds can be 

used in agricultural settings, as well as to reduce loading from urban storm water runoff 

sources (Holdren et al. 2001; Lee and Jones-Lee 2002). A 30-hectare wetland was 

constructed to filter out the effluent from a wastewater treatment plant in Sweden 

(Annadotter et al. 1999). The effluent previously drained directly into very eutrophic 

Lake Finjasjon. After the wetland become operative, the lake Secchi depth increased 

from 0.9 to 1.5 meters, chlorophyll-a concentrations decreased and total phosphorous 

decreased by 25%. The use of wetlands as filters has long been established. 

Watershed Best Management Practices 

There are many additional methods to reduce watershed loading of nutrients to 

water bodies. People may implement Best Management Practices, activities or structures 

to prevent pollution. In agricultural systems, fertilizer input rates can be tailored to the 

specific soil types and crop yields of individual plots, thereby reducing the likelihood of 

applying excess nutrients to the watershed. Soil erosion and corresponding P losses can 

be further reduced by contour farming, strip cropping, or setting up permanent vegetative 

cover. There are currently little data in California with which to compare the 

effectiveness of these methods for reducing loading of bioavailable nutrients (Lee and 

Jones-Lee 2002). 

For water bodies surrounded by residential development, landowners can be 

encouraged to properly construct and maintain septic systems, and limit shoreline 

erosion, to reduce the risk of nutrient loading. In some cases, wastewater treatment 

facilities can be improved to reduce point source nutrient loading, and significantly 

improve overall water quality (Williams 2001). There are many resources available to 

develop a wide array of additional Best Management Practices (Holdren et al. 2001). 
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RELATIVE RELIANCE ON CONVENTIONAL PESTICIDES VS. 

ALTERNATIVE METHODS 

There was variation among different regions and practitioners in the extent of 

conventional chemical versus alternative methods used. These differences result from 

local, regional, and statewide differences in legal restrictions, varying experiences with 

feasibility of alternative methods, and amount of resources available to specific 

organizations. 

Not surprisingly, alternative methods are practiced most extensively in locations 

where conventional pesticides are banned, strongly opposed by the public, or extremely 

difficult to permit. For example, in the Adirondack State Park in New York, conventional 

pesticides are highly restricted, resulting in exclusive reliance on alternative methods. 

Within the park, local lake management agencies attempt to control Eurasian watermilfoil 

with hand harvesting, benthic barriers, grass carp, and suction harvesting, depending on 

the degree of infestation (Hilary Oles, pers. comm.). In less regulated areas of New York 

State, many lake management associations apply for permits to apply fluridone or other 

conventional chemical pesticides (Nancy Mueller, pers. comm.). 

Vermont tends not to rely on chemical methods because of public perception, and 

because one of the major concern lakes, Lake Champlaign, is on the border of VT, NY, 

and Canada, making regulations for chemical use very complex and difficult to address. 

The costs would be high to deal with the regulatory challenge of applying chemicals. The 

predominant methods are mechanical harvesting and hand pulling, with lesser reliance on 

diver operated suction dredging and chemical application (Ann Bove, pers. comm.). 

Recently, however, Vermont approved the use of whole-lake fluridone treatment for the 

control of Eurasian watermilfoil in two Vermont lakes (Getsinger et al., 2002). 

Sometimes, within states with heavy reliance on conventional chemicals, 

localized infestations can be effectively managed using alternative methods. The 

Ichetucknee River in Florida is a good example of a high profile area where public 

interest has been harnessed to develop an effective hand-removal campaign. In this river, 

a three-mile stretch of water lettuce infestation has been effectively controlled using 

hand removal alone. Chemical pesticide applications were ruled out because the river is 
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extensively used for recreational water sports and is also perceived as having high natural 

value that needs to be protected. The local hand-removal program effectively capitalizes 

on the high popularity and strong sense of stewardship for the river. Nine times per year, 

the local management agency recruits a crew of between 15 and 90 volunteer laborers, 

who manually harvest the water lettuce. Additionally, a permanent staff member 

“nitpicks,” laboring every day to remove young water lettuce plants from among native 

vegetation. This extensive coordination has resulted in successful control of a very hardy 

invasive species. Meanwhile, at the statewide level, Florida management agencies rely 

predominantly on conventional chemicals to control water hyacinth and other noxious 

invasives (Fritzi Olson, pers. comm.). 

Despite examples of alternative successes, many regions and agencies rely 

predominantly or exclusively on chemical pesticides, based on previous experience that 

the chemical pesticides were more cost-effective. For example, in Delaware Bay, nonnative Phragmites are controlled by glyphosate application. After initial public 

opposition to chemical application, research tests were undertaken to evaluate nonchemical methods, both separately, and in combination with chemical application. The 

test results indicated that only chemical application was effective, resulting in exclusive 

reliance on herbicide application for Phragmites control (Teal and Peterson 2003). 

The majority of aquatic plant management activity in Florida entails application 

of chemical pesticides. Numerous insect species have been introduced for biological 

control with varying success, but mechanical control efforts are restricted to high use 

areas (e.g., alongside bridges), and locations with high water flow velocity. After decades 

of trial and error with biocontrol and mechanical control options, Florida practitioners 

predominantly rely on chemicals, based on funding and institutional limitations, and the 

experience that the chemical pesticides were more effective in most management 

circumstances (Florida Department of Environmental Protection 2003). 

Reliance on chemical pesticides can extend to non-profit conservation 

organizations, such as The Nature Conservancy (TNC). The Ohio chapter of TNC spent 

many years attempting to control invasive emergent species such as reed canary grass and 

Phragmites using mechanical methods. A multi-year effort to interfere with vegetation 
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growth by repeated cutting was unsuccessful. Eventually, TNC Ohio chapter came to the 

realization that their objective of preserving biodiversity on their sites could only be 

effectively achieved by judicious use of chemical herbicide applications. They did not 

have the staff or financial resources to continue mechanical efforts. Currently, they 

routinely use glyphosate, but attempt to minimize total chemical pollution by methods 

such as manually sponging individual plants with chemical, and applying chemical to cut 

stumps (Marleen Kromer, pers. comm.). 

Some states, such as Indiana, use companies partially owned by pesticide 

corporations as plant management specialists, and also have very widespread use of 

chemical control methods. ReMetrix, a company that works closely with the state of 

Indiana, uses remote sensing and other GIS technologies to accurately quantify 

biovolume and distribution of introduced plants. ReMetrix is partially owned by a major 

chemical manufacturer. 

GENERAL PERMITTING REQUIREMENTS FOR NONCHEMICAL METHODS 

Most mechanical methods require the completion of a 1600 permit application 

from the Department of Fish and Game (DFG). The Department of Fish and Game will 

issue a no-fee permit for harvesting projects. No project size limits apply. DFG will 

restrict aquatic weed control during fish spawning season and approvals will be given for 

that time on a case-by-case basis. The disposal of plant material may require additional 

permits (Lake County Water Resource Division 2002). 

Mechanical harvesting might require an endangered species permit from the U.S. 

Fish and Wildlife Service or NOAA Fisheries for anadromous fish species or other listed 

species. In addition, a waste disposal permit for disposing the plant material after 

harvesting might have to be obtained from the Department of Public Works. A California 

Environmental Quality Act (CEQA) document is also sometimes required for potential 

environmental impacts. 

Diver dredging projects may require a federal permit from the U.S. Army Corps 

of Engineers. The necessity for the Corps of Engineers permit is site dependent 

(Washington State Department of Ecology 2001). 
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To stock grass carp in California waters, a planting permit must be obtained from 

the Department of Fish and Game. Also, if inlets or outlets need to be screened, an 

additional permit may be required.

GENERAL DISCUSSION 

We found considerable variation in the amount of research and application among 

the alternative aquatic pest control methods. Some methods, such as grass carp, 

mechanical harvesting, calcium and aluminum based products, and aeration have been 

extensively studied for decades. For these methods, careful discussions with impartial 

experts and current practitioners could significantly help managers determine whether 

application would be appropriate in a given management scenario. Other methods, such 

as terrestrial herbivores, acetic acid amendment, salt application, shading, and use of 

native plants for competition, have been explored on a much more limited basis. For 

these methods, careful documentation of effectiveness and environmental impacts could 

really benefit future practitioners. Many methods have currently only been evaluated in 

research experiments, and have not been refined, or in some cases permitted, for widescale management applications. In California, on the initiative of local Mosquito and 

Vector Control Districts, a variety of fishes and one invertebrate species are currently 

being evaluated as alternative mosquito predators. Nationwide, plant pathogens and 

cyanobacteria control agents are current research topics, where more funding is needed 

before they can be applied in the field. Peer reviewed research on commercially available 

biocontrol agents suggests that, despite their popularity in the field, they are not effective 

for aquatic algae control. 

Like permitted chemical pesticides, alternative aquatic pest control methods, 

when used improperly, can present environmental risks to aquatic ecosystems. In some 

situations, mechanical methods such as harvesting and rotovation could actually increase 

an aquatic plant infestation over the long-term, or cause the infestation to spread more 

rapidly to new areas. Introduction of new plant or animal species for use in biocontrol can 

have unintended consequences on an aquatic ecosystem. Caution is particularly 

warranted with introduction of non-native biocontrol species, given the fact that unlike 

chemical and mechanical pest control methods, introduced plants or animals could 
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reproduce and spread to new water bodies, causing permanent ecological changes in 

widespread areas. The sterile grass carp program in California is a good example of a 

program with regulatory mechanisms in place to reduce the likelihood of widespread 

adverse impacts. 

Preventive measures are sometimes overlooked as methods to control future 

spread of aquatic infestations. Extensive resources and effort are spent to control nonnative aquatic weeds, with the potential for adverse environmental impacts. It would be 

appropriate for decision-makers in California to consider whether sufficient 

organizational effort is currently being targeted to preventive measures such as early 

detection, quarantine, and regulation of aquatic plant transport. 

For a successful and cost effective non-chemical weed control program, managers 

should assess the environmental conditions, physical characteristics, and use of the water 

body in detail. They should then make a decision regarding appropriate treatment 

methods based on this evaluation. To avoid budgetary constraints in the long run, all 

factors have to be taken into account, and the most effective and least disruptive control 

method should be determined. Appendix C of this report provides a summary framework 

for managers to decide whether some of the most commonly used plant control methods 

may be appropriate for a particular management circumstance in California. 

In many weed management situations a mix of techniques, possibly including 

non-chemical and chemical methods, will be appropriate. Currently, research on 

integrated approaches involving multiple methods is limited (Van Vierssen et al. 2001). 

Novel application and evaluation of integrated approaches should hopefully control 

nuisance aquatic species, while minimizing potential negative environmental effects. 

REFERENCES 

Anderson, L. W. J. 2003. Effects of the natural product herbicide acetic acid on Spartina 

alterniflora. Draft report to Coastal Conservancy. USDA-ARS Exotic and Invasive Weed 

Research. Davis, CA. 18 pp. 

Anderson, L. W. J., Pirosko, C., Holmberg, D., Gee, D. and R. Duvall. 2000. Dissipation 

and movement of Sonar and Komeen following typical applications for control of Egeria 

densa in the Sacramento/San Joaquin Delta and production and viability of E. densa
Aquatic Pesticide Monitoring Program 

Review of Alternative Aquatic Pest Control Methods For California Waters

63 

fragments following mechanical harvesting (1997/1998). In: Environmental Impact 

Report: Egeria densa control program Volume II: Research trial reports. California 

Department of Boating and Waterways. March, 2000. 

http://www.dbw.ca.gov/PDF/EIR/Vol_2/1%20-%20Anderson%20Report.pdf

Alam, S.K., Ager, L.A. and T.M. Rosegger. 1996. The effects of mechanical harvesting 

of floating plant tussock communities on water quality in Lake Istokpoga, Florida. 

Journal of Lake and Reservoir Management. 12(4): 455-461. 

Annadotter, H., Cronberg, G., Aagren, R., Lundstedt, B., Nilsson, P., and S. Strobeck. 

1999. Multiple techniques for lake restoration. In D.M. Harper, B. Brierley, A.J.D. 

Ferguson and G. Phillips (eds), The Ecological Bases for Lake and Reservoir 

Management. Hydrobiologia. 395/396: 77-85. 

Aquatic Plant Information Retrieval Service (APIRS) at the University of Florida. 

http://plants.ifas.ufl.edu/search80/NetAns2/

Armitage, P.D., Blackburn, J.H., Winder, J.M. and J.F. Wright. 1994. Impact of 

vegetation management on macroinvertebrates in chalk streams. Aquatic Conservation. 

4: 95-104. 

Barko, J.W., Adams, M.S. and N.L. Clesceri. 1986. Environmental factors and their 

consideration in the management of submersed aquatic vegetation: A review. Journal of. 

Aquatic Plant Management, 24:1-10. 

Barko, J.W. and R.M. Smart. 1986. Sediment-related mechanisms of growth limitation in 

submersed macrophytes. Ecology. 67(5): 1328-1340. 

Barrett, P.R.F., Curnow, J.C. and J.W. Littlejohn. 1996. The control of diatom and 

cyanobacterial blooms in reservoirs using barley straw. Hydrobiologia. 340: 307-311. 

BBMWD. 2003. Aquatic plant control. Big Bear Municipal Water District Website. 

http://www.bbmwd.org/aquatic.htm

Beutel, M.W. and A.J. Horne. 1999. A review of the effects of hypolimnetic 

oxygenation on lake and reservoir water quality. Journal of Lake and Reservoir 

Management. 15(4): 285-297. 

Booms, T.L. 1999. Vertebrates removed by mechanical weed harvesting in Lake 

Keesus, Wisconsin. Journal of Aquatic Plant Management. 37: 34-36. 

Boylan, J.D. and J.E. Morris. 2003. Limited effects of barley straw on algae and 

zooplankton in a midwestern pond. Journal of Lake and Reservoir Management. 19(3): 

265-271. 
Aquatic Pesticide Monitoring Program 

Review of Alternative Aquatic Pest Control Methods For California Waters

64 

Boylen, C.W., Eichler, L.W. and J.W. Sutherland. 1996. Physical control of Eurasian 

watermilfoil in an oligotrophic lake. Hydrobiologia. 340: 213-218. 

Brakhage, D. 1994. Comments on the Symposium. In: Proceedings of the Grass Carp 

Symposium, 7-9 March 1994, Gainesville, Florida. United States Army Engineer 

Waterways Experiment Station, Vicksburg, Mississippi. pp. 239-240. 

Carpenter, S. R. 1980. Enrichment of Lake Wingra, Wisconsin, by submersed 

macrophyte decay. Ecology. 61(5): 1145-1155. 

Carpenter, S.R. 1981. Submersed vegetation: an internal factor in lake ecosystem 

succession. The American Naturalist. 118(3): 372-383. 

Carpenter, S.R. 1983. Submersed macrophyte community structure and internal loading: 

relationship to lake ecosystem productivity and succession. In: Lake Restoration, 

Protection and Management. US EPA. 105-111. 

Carpenter, S.R. and M.S. Adams. 1977. The macrophyte tissue nutrient pool of a 

hardwater eutrophic lake: implications for macrophyte harvesting. Aquatic Botany. 3: 

239-255. 

Carpenter, S.R. and M.S. Adams. 1978. Macrophyte control by harvesting and 

herbicides: implications for phosphorus cycling in Lake Wingra, Wisconsin. Journal of 

Aquatic Plant Management. 16: 20-23. 

Carpenter, S.R. and A. Gasith. 1978. Mechanical cutting of submersed macrophytes: 

immediate effects on littoral water chemistry and metabolism. Water Research. 12: 55-

57. 

Carpenter, S.R. and J.K. Greenlee. 1981. Lake deoxygenation after herbicidal use: a 

simulation model analysis. Aquatic Botany. 11: 173-186. 

Carpenter, S.R., Kitchell, J.F., Hodgson, J.R., Cochran, P.A., Elser, J.J., Elser, M.M., 

Lodge, D.M., Kretchmer, D., He, X. and C.N. von Ende. 1987. Regulation of lake 

primary productivity by food web structure. Ecology. 68(6): 1863-1876. 

Carpenter, S.R. and J.F. Kitchell. 1988. Consumer control of lake productivity. 

BioScience 38: 764-769. 

CDBW. 2001. Environmental Impact Report: Egeria densa control program. California 

Department of Boating and Waterways. March, 2001. 

http://www.dbw.ca.gov/PDF/EIR/eir.pdf

CDFA. 2003a. CDFA Hydrilla Program: Annual Progress Report For 1999-2000. 

California Department of Food and Agriculture. 

http://www.cdfa.ca.gov/phpps/ipc/hydrilla/hydrilla_annrpt.htm
Aquatic Pesticide Monitoring Program 

Review of Alternative Aquatic Pest Control Methods For California Waters

65 

CDFA. 2003b. California Plant Quarantine Manual. Pest Exclusion Branch, Plant Health 

and Pest Prevention Services Devision, CDFA. 

http://www.cdfa.ca.gov/phpps/pe/pqm.htm

Charudattan, R. and A. Dinoor. 2000. Biological control of weeds using plant 

pathogens: accomplishments and limitations. Crop Protection. 19: 691-695. 

Charudattan, R., Chandramohan, S. and G.S. Wyss. 2002. Biological Control. In W.B. 

Wheeler (ed), Pesticides in Agriculture and the Environment. Marcel Dekker, Inc. 25-

58. 

Chiayvareesajja, S. and C.E. Boyd. 1993. Effects of zeolite, formalin, bacterial 

augmentation and aeration on total ammonia nitrogen compounds. Aquaculture. 116: 

33-45. 

Colle, D.E. and J.V. Shireman. 1994. Use of grass carp in two Florida lakes, 1975 to 

1994. In: Proceedings of the Grass Carp Symposium, 7-9 March 1994, Gainesville, 

Florida. US Army Engineer Waterways Experiment Station, Vicksburg, Mississippi. pp. 

111-120. 

Condon, P. 2003. Weed gets reprieve – state will study milfoil in lake more before taking 

action. The Olympian. July 18, 2003. 

http://www.theolympian.com/home/specialsections/StateGovernment/20030718/54802.s

html

Cooke, G.D., Lombardo, P. and C. Brant. 2001. Shallow and deep lakes: determining 

successful management options. Lakeline. 21: 42-46. 

Coops, H. and S.H. Hosper. 2002. Water level management as a tool for the restoration 

of shallow lakes in the Netherlands. Lake and Reservoir Management. 18(4): 293-298 

Cowell, B.C., Clinton, J.D., Gardiner, W.E. and S.M. Scheda. 1987. The influence of 

whole lake aeration on the limnology of a hypereutrophic lake in central Florida. 

Hydrobiologia. 148: 3-24. 

Creed, R.P. and S.P. Sheldon. 1993. The effects of feeding by a North American weevil, 

Euhrychiopsis lecontei, on Eurasian water milfoil (Myriophyllum spicatum). Aquatic 

Botany. 45: 245-256. 

Creed, R.P. and S.P. Sheldon. 1995. Weevils and water milfoil decline: did a North 

American herbivore cause a decline of an exotic weed in a Vermont lake? Ecological 

Applications. 5: 1113-1121. 
Aquatic Pesticide Monitoring Program 

Review of Alternative Aquatic Pest Control Methods For California Waters

66 

Crowell, W., Troelstrup, N. Jr., Queen, L. and J. Perry. 1994. Effects of harvesting on 

plant communities dominated by Eurasian water milfoil in lake Minnetonka, Mn. Journal 

of Aquatic Plant Management. 32: 56–60. 

Cuda, J.P.,Hornby, J.A., Cotterill, B. and M. Cattell. 1997. Evaluation of Lagenidium 

giganteum for biocontrol of Mansonia mosquitoes in Florida (Diptera: Culicidae). 

Biological Control. 8: 124-130. 

DiTomaso, J.M. and E.A. Healy. 2003. Aquatic and Riparian Weeds of the West. 

University of California. 442 pp. 

Duvall, R.J., Anderson, L.W.J. and C.R. Goldman. 2001. Pond enclosure evaluations of 

microbial products and chemical algaecides used in lake management. Journal of 

Aquatic Plant Management. 39: 99-106. 

Duval, R.J. and L.W.J. Anderson. 2001. Laboratory and greenhouse studies of microbial 

products used to biologically control algae. Journal of Aquatic Plant Management. 39: 

95-98. 

Eichler, L.W., Bombard, R.T., Sutherland, J.W. and C.W. Boylen. 1995. Recolonization 

of the littoral zone by macrophytes following the removal of benthic barrier material. 

Aquatic Plant Management. 33: 51-54. 

Engel, S. 1990. Ecological impacts of harvesting macrophytes in Halverson Lake, 

Wisconsin. Journal of Aquatic Plant Management. 28: 41-45. 

Fast, A.W. and C.E. Boyd. 1992. Water circulation, aeration and other management 

practices. In A.W. Fast and L.J. Lester (eds), Marine Shrimp Culture: Principles and 

Practices. Elsevier Science Publishers B.V. 862 pp. 

Filizadeh, Y. and K.J. Murphy. 2002. Response of sago pondweed to combinations of 

low doses of diquat, cutting and shading. Journal of Aquatic Plant Management. 40: 72-

76. 

Fiske, S. 1999. Benthic macroinvertebrate assessment of water chestnut (Trapa natans)

mechanical shredder treatment from two sites in Lake Champlain. Department of 

Environmental Conservation. Biomonitoring and Aquatic Studies Section. Waterbury, 

VT.

Florida Department of Environmental Protection. 2003. Status of the aquatic plant 

maintenance program in Florida public waters Annual Report fiscal year 2001-2002. 

Florida Department of Environmental Protection Bureau of Invasive Plant Management. 

44 pp. plus Appendix. http://www.dep.state.fl.us/lands/invaspec/Aquatic_3.pdf
Aquatic Pesticide Monitoring Program 

Review of Alternative Aquatic Pest Control Methods For California Waters

67 

Fox, A.M., Haller, W.T. and J. P. Cuda. 2002. Impacts of carbohydrate depletion by 

repeated clipping on the production of subterranean turions by dioecious hydrilla. 

Journal of Aquatic Plant Management. 40: 99-104. 

Garner, P., Bass, J.A.B. and G.D. Collett. 1996. The effects of weed cutting upon the 

biota of a large regulated river. Aquatic Conservation: Marine and Freshwater 

Ecosystems. 6: 21-29. 

Getsinger, K.D., R.M. Stewart, J.D. Madsen, A.S. Way, and C.S. Owens. 2002. Use of 

whole-lake fluridone treatments to selectively control Eurasian watermilfoil in Burr Pond 

and Lake Hortonia, Vermont. Report Number ERDC/EL TR-02-39. U.S. Army Corps of 

Engineers and Vermont Department of Ecology. November, 2002. 146 pp. 

http://www.wes.army.mil/el/elpubs/pdf/trel02-39.pdf

Gibbons, M.V., Gibbons, H.L. and R.E. Pine. 1987. An Evaluation of a Floating 

Mechanical Rototiller for Eurasian Water milfoil Control. Washington State Department 

of Ecology. Publication Number 87-17. 

Gibbons, M.V., Gibbons, H.L. and M.D. Sytsma. 1994. A Citizen’s Manual for 

Developing Integrated Aquatic Vegetation Management Plans. Washington State 

Department of Ecology. Publication Number 93-93. 

Gibbons, M.V., Rosenkranz, M.G., Gibbons, Jr, H.L. and M.D. Sytsma. 1999. Guide for 

Developing Integrated Aquatic Vegetation Management Plans in Oregon. Center For 

Lakes and Reservoirs, Portland State University, Portland, OR. 

http://www.clr.pdx.edu/publications.html

Giri, B.J. III and C.E. Boyd. 2000. Effects of frequent, small doses of calcium carbonate 

on water quality and phytoplankton in channel catfish ponds. North American Journal of 

Aquaculture. 62: 225-228. 

Godfrey, K.E. and L.W.J. Anderson. 1994. Feeding by Bagous affinis (Coleoptera: 

Curculionidae) inhibits germination of hydrilla tubers. Florida Entomol. 77: 480-488. 

Godfrey, K.E., L.W.J. Anderson, S.D. Perry and N. Dechoretz. 1994. Over wintering 

and establishment potential of Bagous affinis (Coleoptera: Curculionidae) on Hydrilla 

verticillata (Hydrocharitaceae) in Northern California. Florida Entomol. 77: 221-230. 

Godfrey, K.E., L.W.J. Anderson, C.E. Turner and M.J. Pitcairn. 1995. Final report on 

research on Hydrellia pakistanae Deonier (Diptera: Ephydridae). California Department 

of Food and Agriculture. 35 pp. 

Gopal, B. 1987. Water Hyacinth. Elsevier. Amsterdam-Oxford-New York-Tokyo. 471 

pp. 
Aquatic Pesticide Monitoring Program 

Review of Alternative Aquatic Pest Control Methods For California Waters

68 

Gourd, T. and T. Ferrell. 2003a. Perennial weed control using the Atarus Ranger Propane 

Flamer and the Sioux Weed Blaster Steamer in a non-cropland environment. Unpublished 

report. Colorado State University Cooperative Extension. Brighton, CO. 5 pp. 

Gourd, T. and T. Ferrell. 2003b. Perennial weed control using the Atarus Ranger Propane 

Flamer in a non-cropland environment. Unpublished report. Colorado State University 

Cooperative Extension. Brighton, CO. 4 pp. 

Gourd, T. and T. Ferrell. 2003c. Annual weed control using the Atarus Ranger Propane 

Flamer and the Sioux Weed Blaster Steamer in a non-cropland environment. Unpublished 

report. Colorado State University Cooperative Extension. Brighton, CO. 3 pp. 

Gunnison, D. and J.W. Barko. 1989. The rhizosphere ecology of submersed 

macrophytes. Water Resources Bulletin. 25: 193-201. 

Hamel, K.S. and J.K. Parsons. 2001. Washington’s Aquatic Plant Quarantine. Journal 

of Aquatic Plant Management. 39: 72-75. 

Helsel, D.R., Gerber, D.T. and S. Engel. 1996. Comparing spring treatments of 2,4-D 

with bottom fabrics to control a new infestation of Eurasian water milfoil. Journal of 

Aquatic Plant Management. 34: 68-71. 

Helsel, D.R., Nichols, S.A. and R.S. Wakeman. 1999. Impact of aquatic plant 

management methodologies on Eurasian water milfoil populations in Southeast 

Wisconsin. Journal of Lake and Reservoir Management. 15(2): 159-167. 

Hill, M.P. and T. Olckers. 2001. Biological control initiatives against water hyacinth in 

South Africa: constraining factors, success and new courses of action. In M.H. Julien, 

M.P. Hill, T.D. Center and D. Jianqing (eds), Biological and integrated control of water 

hyacinth, Eichhornia crassipes. Proceedings of the Second Meeting of the Global 

Working Group for the Biological and Integrated Control of Water Hyacinth. Beijing, 

China. 33-38. 

Holdren, C., Jones, W. and J. Taggart. 2001. Managing lakes and reservoirs. North 

American Lake Management Society and Terrene Inst., in Coop. with Office of Water, 

Assessment and Watershed Protection Division, U.S. EPA. Madison, WI. 381 pp. 

Horne, A.J. and C.R. Goldman. 1994. Limnology. 2nd ed. McGraw Hill. 576 pp. 

ISP 2003. Draft Programmatic Environmental Impact Statement/Environmental Impact 

Report. San Francisco Estuary Invasive Spartina Project: Spartina Control Program. 

April, 2003. http://www.spartina.org/project_documents/eis_draft.htm

James, W.F., Barko, J.W. and H.L. Eakin. 2002. Water quality impacts of mechanical 

shredding of aquatic macrophytes. Journal of Aquatic Plant Management. 40: 36-42. 
Aquatic Pesticide Monitoring Program 

Review of Alternative Aquatic Pest Control Methods For California Waters

69 

Jaynes, M.L. and S.R. Carpenter. 1985. Effects of submersed macrophytes on 

phosphorus cycling in surface sediment. North American Lake Management Society. 4: 

370-374. 

Johnson, C.S. 2001. Invasion of “killer” Mediterranean weed to California, USA. 

Intercoast Network – International Newsletter of Coastal Management. 2 pp. 

http://www.crc.uri.edu/comm/download/IC_40/Johnson.pdf

Joyce, J. C. 1992. Impact of Eichhornia and Hydrilla in the United States. In C. 

Sinderman, B. Steinmetz, and W. Hershberger (eds), Introductions and Transfer of 

Aquatic Species. ICES Mar. Sci. Symp. 194: 106-109. 

Kay, S.H. and S.T. Hoyle. 2001. Mail order, the internet, and invasive aquatic weeds. 

Journal of Aquatic Plant Management. 39: 88-91. 

Killgore, K.J. and J.P. Kirk. 1998. Littoral fishes response, Upper Lake Marion, 

SC, following triploid grass carp hydrilla control. Aquatic Plant Control Technical 

Note MI-01. U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS. 

www.wes.army.mil/el/aqua/aqtn.html

Killgore, K.J., Kirk, J.P. and J.W. Foltz. 1998. Response of littoral fishes in Upper Lake 

Marion, South Carolina following hydrilla control by triploid grass carp. Journal of 

Aquatic Plant Management. 36: 82-87. 

Kimbel, J.C. and S.R. Carpenter. 1981. Effects of mechanical harvesting on 

Myriophyllum spicatum L. regrowth and carbohydrate allocation to roots and shoots. 

Aquatic Botany. 11: 121-127. 

Kitchell, J.F. (ed.). 1992. Food web management: a case study of Lake Mendota. 

Springer-Verlag, New York. 

Klotz, R.L. and S.A. Linn. 2001. Influence of factors associated with water level 

drawdown on phosphorus release from sediments. Journal of Lake and Reservoir 

Management. 17(1): 48-54. 

Kretsch, K. 2003. An automated aquatic weed control system for shoreline property 

owners. Abstract from the 22nd Annual Conference (2003) of the Western Aquatic Plant 

Management Society, Sacramento, CA. 

Lake County, Water Resource Division Website. 1999. 1999 Aquatic Weed Pilot Project. 

http://watershed.co.lake.ca.us/programs/aquaticplants/pilotproject.html

Lake County, Water Resource Division Website. 2002. Clear Lake Aquatic Weed 

Control Permit. Guide to the Clear Lake Aquatic Plant Management Program, 2002. 

http://watershed.co.lake.ca.us/programs/aquaticplants/aquaticweedpermit.html 
Aquatic Pesticide Monitoring Program 

Review of Alternative Aquatic Pest Control Methods For California Waters

70 

Lake Minnetonka Conservation District. 2002. 2002 Eurasian Water Milfoil (EWM) 

Final Harvesting Report. Deephaven, MN, 55391. 

http://www.winternet.com/~lmcd/pdf/EWM%20Harvesting%20Report/EWM%20Final%

20Harvesting%20Season%20Report-%202002.pdf

Lee, G. F. and A. Jones-Lee. Review of management practices for controlling the water 

quality impacts of potential pollutants in irrigated agriculture storm water runoff and tail 

water discharges. California Water Institute Report TP 02-05 to California Water 

Resources Control Board/Central Valley Regional Water Quality Control Board. 

California State University Fresno. Fresno, CA. 128 pp. 

http://www.gfredlee.com/BMP_Rpt.pdf

Lembi, C.A. 1996. Assessment of 2,4-D Use in Aquatic Systems in the United States. 

Chapter 12 In Biologic and Economic Assessment of Benefits from Use of Phenoxy 

Herbicides in the United States. U.S. Department of Agriculture, NAPIAP Report No. 1-

PA-96. http://www.24d.org/Frontpg.pdf; http://www.24d.org/chaptr12.pdf

Lembi, C.A. 2002. Aquatic Plant Management: Barley Straw for Algae Control. APM-1-

W. Department of Botany and Plant Pathology, Purdue University. 

http://www.btny.purdue.edu/Pubs/APM/APM-1-W.pdf

Leslie, A.J., Nall, L.E., Jubinsky, G.P. and J.D. Schardt. Effects of grass carp on the 

aquatic vegetation in Lake Conway, Florida. In: Proceedings of the Grass Carp 

Symposium, 7-9 March 1994, Gainesville, Florida. US Army Engineer Waterways 

Experiment Station, Vicksburg, Mississippi. pp. 121-128. 

http://www.dep.state.fl.us/lands/invaspec/2ndlevpgs/pdfs%20for%20pubs/Conway94.pdf

Leslie, A.J., Nall, L.E., Jr. and D.C. Schmitz. 1986. The effects of aeration on the 

shoreline fishes of a eutrophic Florida lake. Florida Department of Natural Resources, 

Bureau of Aquatic Plant Research and Control. Tallahassee, Fl. 

http://www.dep.state.fl.us/lands/invaspec/2ndlevpgs/pdfs%20for%20pubs/brookr3.pdf

Lounibos, L.P., Nishimura, N. and L.B. DeWald. 1992. Predation of Mansonia (Diptera: 

Culicidae) by native mosquitofish in Southern Florida. Entomological Society of 

America. 29: 236-241. 

Madsen, J.D. 1990. Water chestnut (Trapa natans L.) research in Watervliet reservoir – 

1989 report. Prepared for the City of Watervliet, New York. 

Madsen, J. D. 1997. Methods for management of nonindigenous aquatic plants. In: 

Luken, J. O., Thieret, J. W. (Eds.). Assessment and Management of Plant Invasions. 

Springer, New York, pp. 145-171. 

Madsen, J. D. 2002. Advantages and disadvantages of aquatic plant management 

techniques. Technical Report TR-02-11, June 2002 US Army Corps of Engineers, 

Waterways Experiment Station. http://www.aquatics.org/pubs/madsen2.htm
Aquatic Pesticide Monitoring Program 

Review of Alternative Aquatic Pest Control Methods For California Waters

71 

Madsen, J.D., Adams, M.S. and P. Ruffier. 1988. Harvest as a control for sago 

pondweed (Potamogeton pectinatus L.) in Badfish Creek, Wisconsin: frequency, 

efficiency and its impact on the stream community oxygen metabolism. Journal of 

Aquatic Plant Management. 26: 20-25. 

Madsen, J.D., Getsinger, K.D., Stewart, R.M., Skogerboe, J.G., Honnell, D.R. and C.S. 

Owens. 1999. Evaluation of transparency and light attenuation by AquashadeTM.

Journal of Lake and Reservoir Management. 15(2): 142-147. 

Madsen, J.D., Grodowitz, M.J., Stewart, R.M., Whitaker, S. and L. Jeffers. 1998. 

Computer tools developed for aquatic plant management. Journal of Aquatic Plant 

Management. 36: 78-82. 

Madsen, J.D., Luu, K.T., and K.D. Getsinger. 1993. Allocation of Biomasss and 

carbohydrates in water hyacinth (Eichhornia crassipes): pond-scale verification. United 

States Army Corps of Engineers, Waterways Experiment Station. 

Major, W.W. III, Grue, C.E., Grassley, J.M. and L.L. Conquest. 2003. Mechanical and 

chemical control of smooth cordgross in Willapa Bay, Washington. Journal of Aquatic 

Plant Management. 41: 6-12. 

Maldonado, D.C. 2001. Aquatic weed control in Salt River Project canals. Abstract from 

the 20th Annual Conference (2001) of the Western Aquatic Plant Management Society, 

Bozeman, Montana. http://www.wapms.org/abstracts/abstracts01.html

Mann, R. 2003. Methodology For Aquatic Plant Management Economics. In Mann, R. 

and M. Wittmann. 2003. Determining Economic Impacts of Aquatic Plant Management 

in California Waters. APMP Technical Report. SFEI Contribution #94. San Francisco 

Estuary Institute, Oakland, CA and RMEcon, Davis, CA. pp. 2 - 68.

http://www.sfei.org/apmp/recent_pubs.html

Martin, D. and I. Ridge. 1999. The relative sensitivity of algae to decomposing barley 

straw. Journal of Applied Phycology. 11: 285-291. 

Masuda, K. and C.E. Boyd. 1994. Effects of aeration, alum treatment, liming and 

organic matter application on phosphorus exchange between soil and water in 

aquaculture ponds at Auburn, Alabama. Journal of the World Aquaculture Society. 25-

3: 405-416. 

McCann, J.A., Arkin, L.N. and J.D. Williams. 1996. Nonindigenous aquatic and 

selected terrestrial species of Florida - status, pathway and time of introduction, present 

distribution, and significant ecological and economic effects. National Biological Service, 

Southeastern Biological Science Center. Gainesville, FL. 

http://aquat1.ifas.ufl.edu/mctitle.html
Aquatic Pesticide Monitoring Program 

Review of Alternative Aquatic Pest Control Methods For California Waters

72 

Meinesz, A. 1999. Killer algae – the true tale of a biological invasion. University of 

Chicago Press. Chicago, IL. 360 pp. 

Methe, B.A., Soracco, R.J., Madsen, J.D. and C.W. Boylen. 1993. Seed production and 

growth of water chestnut as influenced by cutting. Journal of Aquatic Plant 

Management. 31: 154-157. 

Mikol, G.F. 1985. Effects of Harvesting on Aquatic Vegetation and Juvenile Fish 

Populations at Saratoga Lake, New York. Journal of Aquatic Plant Management. 23: 59-

63. 

Miller, C. 2003. Biological control of mosquitoes with the Sacramento perch (Archoplites 

interrruptus). Unpublished report. Contra Costa Mosquito and Vector Control District. 

Concord, CA. 5 pp. 

Minnesota Department of Natural Resources. 2004. Aquatic plant management 

regulations. http://www.dnr.state.mn.us/shorelandmgmt/apg/regulations.html

Mizumoto, M. 2000. An update on the eradication of hydrilla in the Imperial Valley. 

Abstract from the 19th Annual Conference (2000) of the Western Aquatic Plant 

Management Society, Bozeman, Montana. 

http://www.wapms.org/abstracts/abstracts00.html

Monahan, C. and J.M. Caffrey. 1996. The effect of weed control practices on 

macroinvertebrate communities in Irish Canals. Hydrobiologia. 340: 205-211. 

Monnelly, A., Straub, J. and K. Wagner. 2003. Plant replacement as a management 

technique for controlling Eurasian watermilfoil: initial results and two-year follow up 

from a plant replacement pilot program in lake Buel, MA. Abstract from the 2003 Annual 

Conference (2003) of the Northeast Aquatic Plant Management Society. 

Nelson, L.S. and J.F. Shearer. 2002. Response of Eurasian water milfoil to integrated 

fluridone-fungal pathogen treatment. APCRP. July: 1-8. 

Nelson, L.S., Shearer, J.F. and M.D. Netherland. 1998. Mesocosm evaluation of 

integrated fluridone-fungal pathogen treatment on four submersed plants. Journal of 

Aquatic Plant Management. 36: 73-77. 

Netherland, M.D. and J.F. Shearer. 1996. Integrated use of fluridone and a fungal 

pathogen for control of hydrilla. Journal of Aquatic Plant Management. 33: 4-8. 

Nichols, S.A. and R.C. Lathrop. 1994. Impact of harvesting on aquatic plant 

communities in Lake Wingra, Wisconsin. Journal of Aquatic Plant Management. 32: 33-

36. 

NOAA Fisheries. Office of Protected Resources. Endangered Species Permit Program. 
Aquatic Pesticide Monitoring Program 

Review of Alternative Aquatic Pest Control Methods For California Waters

73 

http://www.nmfs.noaa.gov/prot_res/PR3/Permits/ESAPermit.html

Olson, M.H., Carpenter, S.R., Cunningham, P., Gafny, S., Herwig, B.R., Nibbelink, N.P., 

Pellett, T., Storlie, C. Trebitz, A.S. and K.A Wilson. 1988. Managing macrophytes to 

improve fish growth: a multi-lake experiment. Fisheries Management. 23(2): 6-12. 

Olson, T. 2003. Overview of U.S. Bureau of Reclamation Giant Salvinia control 

activities. Abstract from the 22nd Annual Conference (2003) of the Western Aquatic Plant 

Management Society, Sacramento, California. 

Parker, M.S. and M.D. Sytsma. 1998. Aquatic vegetation management in Southern 

Oregon irrigation canals. Phase II: Evaluation of techniques to prevent and reduce plant 

growth. Report for the Oregon Department of Agriculture and Talent Irrigation District. 

Southern Oregon University, Ashland OR. 28 pp. 

Pauley, G.B., Thomas, G.L., Bonar, S.A., Frodge, J.D., Marino, D.A., Thiesfeld, S.L., 

Vecht, S., Bowers, K.L. and H. Sehgal. 1994. An overview of the use and efficacy of 

triploid grass carp Ctenopharyngodon idella as a biological control of aquatic 

macrophytes in Oregon and Washington state lakes. In: Proceedings of the Grass Carp 

Symposium, 7-9 March 1994, Gainesville, Florida. US Army Engineer Waterways 

Experiment Station, Vicksburg, Mississippi. pp. 46-54. 

Phillips, G., Bramwell, A., Pitt, J., Stansfield, J. and M. Perow. 1999. Practical 

application of 25 years’ research into the management of shallow lakes. In D.M. Harper, 

B. Brierley, A.J.D. Ferguson and G. Phillips (eds), The Ecological Bases for Lake and 

Reservoir Management. Hydrobiologia. 395/396: 61-76. 

Pine, R.T., Anderson, L.W.J. and S.S.O. Hung. 1990. Control of aquatic plants in static 

and flowing water by yearling triploid grass carp. Journal of Aquatic Plant Management. 

28: 36-40. 

Prepas, E.E., Babin, J., Murphy, T.P., Chambers, P.A., Sandland, G.J., Ghadouani, A. 

and M. Serediak. 2001. Long-term effects of successive Ca(OH)2 and CaCO3 treatments 

on the water quality of two eutrophic hardwater lakes. Freshwater Biology. 46: 1089-

1103. 

Prepas, E.E. and J.M. Burke. 1997. Effects of hypolimnetic oxygenation on water 

quality in Amisk Lake, Alberta, a deep, eutrophic lake with high internal phosphorous 

loading rates. Canadian Journal of Fish and Aquatic Science. 54: 2111-2120. 

Quarles, W. 2001. Improved hot water weed control system. IPM Practitioner. 23(1): 1-4. 

Queiroz, J.F. and C.E. Boyd. 1998. Effects of a bacterial inoculum in channel catfish 

ponds. Journal of the World Aquaculture Society. 29: 67-73. 
Aquatic Pesticide Monitoring Program 

Review of Alternative Aquatic Pest Control Methods For California Waters

74 

Randall, S., Harper, D. and B. Brierley. 1999. Ecological and ecophysiological impacts 

of ferric dosing in reservoirs. In D.M. Harper, B. Brierley, A.J.D. Ferguson and G. 

Phillips (eds), The Ecological Bases for Lake and Reservoir Management. 

Hydrobiologia. 395/396: 355-364. 

Reeder, R.H. 2003. International Mycoherbicide Programme for Eichhornia crassipes 

control in Africa (IMPECCA). Proceedings of the Fourth International Bioherbicide 

Workshop. Canberra, Australia. 

Reedyk, S., Prepas, E. and P.A. Chambers. 2001. Effects of single Ca(OH)2 doses on 

phosphorus concentration and macrophyte biomass of two boreal eutrophic lakes over 2 

years. Freshwater Biology. 46: 1075-1087. 

ReMetrix. 2001. Vegetation assessment and management plan for Big Bear Lake (San 

Bernadino County, California). Report prepared for Big Bear Municipal Water District. 

January 10, 2001. Remetrix, LLC. 18 pp. + Appendices. 

Rydin, E. and E.B. Welch. 1998. Aluminum dose required to inactivate phosphate in 

lake sediments. Water Resources. 32: 2969-2976. 

Sabbatini, M.R. and K.J. Murphy. 1996. Response of Callitriche and Potamogeton to 

cutting, dredging and shade in English drainage channels. Journal of Aquatic Plant 

Management. 34: 8-12. 

Salonen, V.P., Varjo, E. and P. Rantala. Gypsum treatment in managing the internal 

phosphorus load from sapropelic sediments:; experiments on Lake Laikkalammi, Finland. 

Boreal Environment Research. 6: 119-129. 

Santha, C.R., Martyn, R.D., Neill, W.H. and K. Strawn. 1994. Control of submersed 

weeds by grass carp in water lily production ponds. Journal of Aquatic Plant 

Management. 32: 29-33. 

Schulthorpe, C.D. 1967. The Biology of Aquatic Vascular Plants. Edward Arnold, 

London, 610 pp. 

Scheffer, M. 1999. Searching explanations of nature in the mirror world of math. 

Conservation Ecology 3(2): 11. http://www.consecol.org/vol3/iss2/art11

Scheffer, M., Hosper, S.H., Meijer, M.L. and B. Moss. 1993. Alternative equilibria in 

shallow lakes. Trends in Ecology and Evolution 8: 275-279. 

Schon, W. 2003a. Guppies (Poecilia reticulata) and their use in California mosquito 

control. Unpublished report. Sacramento – Yolo Mosquito and Vector Control District. 

Elk Grove, CA. 5 pp. 
Aquatic Pesticide Monitoring Program 

Review of Alternative Aquatic Pest Control Methods For California Waters

75 

Schon, W. 2003b. The stickleback family (Gasterosteidae). Unpublished report. 

Sacramento – Yolo Mosquito and Vector Control District. Elk Grove, CA. 5 pp. 

Shearer, J.F. 2002. The potential role of an endophytic fungus in the decline of stressed 

Eurasian water milfoil. Journal of Aquatic Plant Management. 40: 76-78. 

Shearer, J.F. and L.S. Nelson. 2002. Integrated use of endothall and a fungal pathogen 

for management of the submersed aquatic macrophyte Hydrilla verticillata. Weed 

Technology. 16: 224-230. 

Sheldon, S.P. and R.P. Creed, Jr. 2003. The effect of a native biological control agent 

for Eurasian water milfoil on six North American watermilfoils. Aquatic Botany. 76: 

259-265. 

Sheldon, S.P. and L.M. O’Bryan. 1996. The effects of harvesting Eurasian water milfoil 

on the aquatic weevil Euhrychiopsis lecontei. Journal of Aquatic Plant Management. 34: 

76-77. 

Sigee, D.C., Glenn, R., Andrews, M.J., Bellinger, E.G., Butler, R.D., Epton, H.A.S. and 

R.D. Hendry. 1999. Biological control of cyanobacteria: principles and possibilities. In

D.M. Harper, B. Brierley, A.J.D. Ferguson and G. Phillips (eds), The Ecological Bases 

for Lake and Reservoir Management. Hydrobiologia. 395/396: 161-172. 

Smeltzer, E., Kirn, R.A. and S. Fiske. 1999. Long-term water quality and biological 

effects of alum treatment of Lake Morey, Vermont. Journal of Lake and Reservoir 

Management. 15(3): 173-184. 

Sondergaard, M., Jeppesen, E. and J.P. Jensen. 2000. Hypolimnetic nitrate treatment to 

reduce internal phosphorus loading in a stratified lake. Lake and Reservoir Management. 

16(3): 195-204. 

Spencer, D.F. 1984. Oxygen consumption by the crayfish Orconectes propinquus 

(Girard) exposed to aquashade. Bulletin of Environmental Contamination and 

Toxicology. 33: 373-378. 

Spencer, D.F. and G.G. Ksander. 1995a. Differential effects of the microbial metabolite, 

acetic acid, on sprouting of aquatic plant propagules. Aquatic Botany 52: 107-119. 

Spencer, D.F. and G.G. Ksander. 1995b. Influence of acetic acid on regrowth of 

dioecious hydrilla from root crowns. Journal of Aquatic Plant Management 33: 1995. 

Spencer, D.F. and G.G. Ksander. 1997. Dilute acetic acid exposure enhances electrolyte 

leakage by Hydilla verticillata and Potamogeton pectinatus tubers. Journal of Aquatic 

Plant Management 35: 25-30. 
Aquatic Pesticide Monitoring Program 

Review of Alternative Aquatic Pest Control Methods For California Waters

76 

Spencer, D.F. and G.G. Ksander. 1999. Influence of dilute acetic acid treatments on 

survival of monoecious hydrilla tubers in the Oregon House Canal, California. Journal of 

Aquatic Plant Management 37: 67-71. 

Spencer, D.F., Ksander, G.G. and S.R. Bissell. 1992. Growth of monoecious hydrilla on 

different soils amended with peat or barley straw. Journal of Aquatic Plant Management 

30: 9-15. 

Stewart, R.M. and W.A. Boyd. 1999. The grass carp stocking rate model 

(AMUR/STOCK). TN APCRP MI-03. APCRP Technical Notes Collection. U.S. 

Army Engineer Research and Development Center, Vicksburg, MS. 

http://www.wes.army.mil/el/aqua

Su, T. 2003a. Pupfish (Cyprinodontiformes: Cyprinodontidae) and their potential use for 

mosquito control. Unpublished report. Coachella Valley Mosquito and Vector Control 

District. Indio, CA. 6 pp. 

Su, T. 2003b. Tadpole shrimp (Notostraca: Triopsidae), a potential biological control 

agent against immature mosquitoes. Unpublished report. Coachella Valley Mosquito and 

Vector Control District. Indio, CA. 10 pp. 

Systma, M. D. and Parker, M. 1999. Aquatic Vegetation in Irrigation Canals: A Guide to 

Integrated Management. Report for Oregon Department of Agriculture and U.S. EPA. 

Center For Lakes and Reservoirs, Portland State University, Portland, OR. 

http://www.clr.pdx.edu/publications.html

Taylor, S. and G. Gately. 1998. Lake Leland Integrated Aquatic Plant Management Plan. 

Jefferson County Conservation District. 

Teal, J.M and S.B. Peterson. 2003. The interaction between science and policy in control 

of Phragmites in oligohaline marshes of Delaware Bay. Abstract from the 17th Biennial 

Conference of the Estuarine Research Federation, Seattle, Washington. 

Terlizzi, D.E., Ferrier, D.M., Armbrester, E.A. and K.A. Anlauf. 2002. Inhibition of 

dinoflagellate growth by extracts of barley straw. Journal of Applied Phycology, 12:275-

280. 

The Nature Conservancy. 2003. Adirondack Park Invasive Plant Action Plan for the 

Adirondack Park Invasive Plant Program. Prepared by The Nature Conservancy, New 

York State (NYS) Adirondack Park Agency, NYS Department of Environmental 

Conservation, and NYS Department of Transportation. June, 2003. 27 pp. 

Tobiessen, P., Swart, J. and S. Benjamin. 1992. Dredging to control curly-leaved 

pondweed: a decade later. Journal of Aquatic Plant Management. 30: 71-72. 
Aquatic Pesticide Monitoring Program 

Review of Alternative Aquatic Pest Control Methods For California Waters

77 

Unmuth, J.M.L., Sloey, D.J. and R.A. Lillie. 1998. An evaluation of close cut 

mechanical harvesting of Eurasian water milfoil. Journal of Aquatic Plant Management. 

36: 93-100. 

U.S. Army Corps of Engineers. 2001. Aquatic Plant Information System. Version 2. 

Aquatic Plant Control Research Program. U.S. Army Corps of Engineers. 

http://www.wes.army.mil/el/aqua/apis/apishelp.htm

U.S. Army Corps of Engineers. 2002. Mechanical Control of Exotic Aquatic Plants. 

Aquatic Plant Control Operations Support Center (APCOSC), Jacksonville, FL 32232. 

USDA (United States Department of Agriculture) and CDBW (California Department of 

Boating and Waterways). 2003. Water hyacinth control program proposed winter season 

non-chemical control methods. Draft Proposal. 

U.S. Fish and Wildlife Service. Endangered Species Regional Permit Offices. 

http://forms.fws.gov/esrtnaddr.html

Ussery, T.A., Eakin, H.L., Payne, B.S., Miller, A.C. and J.W. Barko. 1997. Effects of 

Benthic Barriers on Aquatic Habitat Conditions and Macroinvertebrate Communities. 

Journal of Aquatic Plant Management. 35: 69-73. 

Van Hullebusch, E., Deluchat, V., Chazal, P.M. and M. Baudu. 2002. Environmental 

impact of two successive chemical treatments in a small shallow eutrophied lake: Part I. 

case of aluminum sulfate. Environmental Pollution. 120: 617-626. 

Van Nes, E. H., van den Berg, M. S., Clayton, J. S., Coops, H., Scheffer, M. and E. van 

Ierland. A simple model for evaluating the costs and benefits of aquatic macrophytes. 

Hydrobiologia. 415: 335-339. 

Van Vierssen, W., Van Hofwegen, P.J.M. and J.E. Vermaat. 2001. The age of water 

scarcity: in search of a new paradigm in aquatic weed control. Journal of Aquatic Plant 

Management. 39: 3-7. 

Varjo, E., Liikanen, A., Salonen, V.P. and P.J. Martikainen. 2003. A new gypsum-based 

technique to reduce methane and phosphorus release from sediments of eutrophied lakes: 

(Gypsum treatment to reduce internal loading). Water Research. 37: 1-10. 

Wagner, T. and C.M. Falter. 2002. Response of an aquatic macrophyte community to 

fluctuating water levels in an oligortrophic lake. Lake and Reservoir Management. 

18(1): 52-65. 

WDFW (Washington State Department of Fish and Wildlife). 1997. Aquatic Plants and 

Fish. Publication Number APF 11-97. 
Aquatic Pesticide Monitoring Program 

Review of Alternative Aquatic Pest Control Methods For California Waters

78 

Washington State Department of Ecology. 2001. Final Supplemental Environmental 

Impact Statement for Freshwater Aquatic Plant Management. Publication Number 00-10-

040. 

Watson, A.K. 2003. Where did it go wrong? Why is the concept of bioherbicide 

suffering from limited success? Proceedings of the Fourth International Bioherbicide 

Workshop. Canberra, Australia. 

Webb, M.A., Elder, H.S., and Howells, R.G. 1994. Grass carp reproduction in the Lower 

Trinity River, Texas. In: Proceedings of the Grass Carp Symposium, 7-9 March 1994, 

Gainesville, Florida. US Army Engineer Waterways Experiment Station, Vicksburg, 

Mississippi. pp. 29-32. 

Welch, E.B. and G.D. Cooke. 1999. Effectiveness and Longevity of Phosphorus 

Inactivation with Alum. Journal of Lake and Reservoir Management. 15(1): 5-27. 

Williams, V.P. 2001. Effects of point-source removal on lake water quality: a case 

history of Lake Tohopekaliga, Florida. Journal of Lake and Reservoir Management. 

17(4): 315-329. 

Wisconsin Department of Natural Resources. 2001. Restoration of Devil’s Lake by 

bottom water withdrawal. Environmental Analysis and Decision on the Need for an 

Environmental Impact Statement (EIS). Prepared by Richard Lathrop, WDNR, Madison, 

Wisconsin. 10 pp. 

Wittenberg, R. and M.J.W. Cock (eds.). 2001. Invasive alien species: a toolkit of best 

prevention and management practices. CAB International. Wallingford, Oxon, UK. 228 

pp. http://www.cabi-bioscience.ch/wwwgisp/

Woodard, S.E. and C.A. Rock. 1995. Control of residential storm water by natural buffer 

strips. Lake and Reservoir Management. 11(1): 37-45. 

Zisette, R. 2001. Eurasian water milfoil control and exotic species prevention in Seattle’s 

Lake Youngs Reservoir. Herrera Environmental Consultants, 2200 Sixth Avenue, Suite 

601, Seattle, WA 98121.
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APPENDIX A: CONTRACTORS/ RETAILERS THAT SPECIALIZE 

IN NON-CHEMICAL CONTROL METHODS 

This listing includes contractors who regularly perform some of the aquatic pest 

control methods described in the literature reviews. All California-based contractors we 

are aware of have been listed. 

Contractors who conduct Non-Pesticide Control Methods 

American Civil Constructors 

3701 Mallard Dr. 

Benicia, CA 94510 

Contact: Dan Palmer 

707-746-8028 x28 

http://www.acconstructors.com/index.html 

Specialties include: mechanical harvesting; mechanical excavation 

Aquatic Environments Inc. 

P.O. Box 1406. 

Alamo, CA 94507 

Contact: George Forni 

925 314-0831 

email: gforni@covad.net 

www.aquaticenvironmentsinc.com/

Specialties include: mechanical harvesting, cutting, and rotovation; mechanical 

excavation; shading; biocontrol (bacteria); aeration; habitat restoration 

Clean Lakes, Inc. 

P.O. Box 3186 

Martinez CA 94553 

Contact: Tom McNabb 

925 - 957 1905 

1-877-FIX-LAKE 

Fax: 925 957-1906 

email: info@cleanlake.com 

www.cleanlake.com

Specialties include: mechanical harvesting and cutting; shading; biocontrol (bacteria); 

aeration 

Environmental Water Works 
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Contact: Steve Walters 

714 801-8546 

email: stevenwalters@msn.com 

Specialties include: mechanical cutting and harvesting on small ponds, biocontrol 

PMC Production 

10173 Croydon Way, Suite 3 

Sacramento, CA 95827 

916 638-8990 

fax: 916 638-8991 

email: info@pmcproduction.com 

http://pmcproduction.com/

Specialties include: mechanical harvesting and cutting 

Southwest Aquatics 

P.O. Box 13212 

Palm Desert, CA 92225 

Contact: Paul Beaty 

760 568-5499 

Fax: 760 568-4019 

email: SWAquatics@aol.com 

Specialties include: small pond management; grass carp 

United Storm Water, Inc. 

14000 E. Valley Blvd., Suite B 

City of Industry, CA 91746-2801 

Contact: Paul Corn 

1-877-71-STORM 

Fax: 626-961-3166 

email: pcorn@unitedstormwater.com 

Specialties include: mechanical excavation and dredging 

Companies that Manufacture and Sell Aquatic Plant Harvesters or Other NonChemical Devices 

Aquamarine 

1444 S. West Avenue, Waukesha 

Wisconsin 53186, USA 

Tel: (262)547-0211 

Fax: (262)547-0718 

E-Mail: weedharvesters@aol.com 

http://www.aquamarine.ca/
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Aquarius Systems 

PO Box 215 

North Prairie, Wisconsin 53153-0215 

262-392-2162 (phone) 

800-328-6555 (toll free) 

262-392-2984 (fax) 

email: info@aquarius-systems.com 

http://www.aquarius-systems.com/

Lake Restoration, Inc. 

12425 Ironwood Circle 

Rogers, Minnesota 55374 

Phone: (763) 428-9777 

Toll free: (877) 428-8898 

Fax: (763) 428-1543 

E-mail: lrmail@lakerestoration.com 

http://www.lakerestoration.com/

Miller Aquatic Technologies LLC 

358 S Main Street, No 86 

Orange, California 92868 

1-714-667-5053 

email: info@milleraquatics.com 

http://www.milleraquatics.com/

PMC Production 

10173 Croydon Way, Suite 3 

Sacramento, CA 95827 

916 638-8990 

fax: 916 638-8991 

email: info@pmcproduction.com 

http://pmcproduction.com/
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APPENDIX B: PRACTITIONERS INTERVIEWED FOR REVIEW 

California Practitioners 

Bob Acker 

Merced Irrigation District 

P.O. Box 2288 

Merced, CA 95344-0288 

(209) 722-5761 

rack@mercedid.org 

Earl Andress 

USDA-APHIS-PPQ-PPPC 

4151 Hwy 86 Bldg 10 

Brawley, CA 92227 

Phone 760-344-7857 

FAX 760-351-0532 

e-mail: eandress@quix.net 

Steve Andrews 

University of California Berkeley 

301 Campbell Hall 

Berkeley, CA 94720-2922 

(510) 381-1321 

sandrews@uclink.berkeley.edu 

Dr. Richard Bailey 

Lake Merritt Institute 

568 Bellevue Avenue 

Oakland, CA 94610 

(925) 314-0531 

lmi@netwiz.net 

Walt Barret 

Golf Course Vegetation Manager 

Green Hills Country Club 

Millbrae, CA 

(650) 588-4616 

Dr. Paul Beaty 

Southwest Aquatics 

P.O. Box 13212 · Palm Desert, CA 92255 

(760) 568-5499 

swaquatics@aol.com 
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Larry Bezark 

California Department of Food and Agriculture 

(916) 654-0768 

Lbezark@cdfa.ca.gov

Dick Bogaert 

Mt. View Sanitary District 

dbogaert@mvsd.org 

Steve Brueggeman 

California Department of Fish and Game 

Mendota Wildlife Refuge 

(559) 655-4645 

Mark Bryant 

Garberville Sanitary District 

P.O. Box 211 

Garberville, CA 95542 

(707) 923-9566 

scs@redwaymail.net 

Jason Churchhill 

Lahontan RWQCB 

(530) 542-5571 

Don Conley 

California Department of Boating and Waterways 

2000 Evergreen Street Suite 100 

Sacramento, CA 95815-3888 

(916) 240-8722 

Bill Cook 

Los Banos Wildlife Area 

18110 W. Henry Miller Rd. 

Los Banos, CA 93635-9508 

(209) 826-0463 

Laura Crum 

California Department of Fish and Game 

South Coast Region (Region 5) 

4665 Lampson Ave., Suite C 

Los Alamitos, CA 90720 

(562)493-6897 (Office) 

lcrum@dfg.ca.gov 

Nate Dechoritz 
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California Department of Food and Agriculture 

Ndechore@cdfa.ca.gov 

1220 N Street, Rm A-357 

Sacramento, CA 94271 

Ron Derma 

Bard Irrigation District 

PO Box 776 

Bard, CA 92222 

(760) 572-0704 

George Forni 

Aquatic Environments, Inc. 

gforni@covad.net 

(925) 314-0831 

Tony Gallegos 

Lake County Water Resources Division 

255 North Forbes Street 

Lakeport, CA 95453 

Telephone: (707) 263-2341 

Fax: (707) 263-7748 

tonyg@co.lake.ca.us 

Cynthia Gause 

California Department of Boating and Waterways 

2000 Evergreen Street Suite 100 

Sacramento, CA 95815-3888" 

(916) 263-1819 

CGause@dbw.ca.gov 

Larry Grabow 

Marin Municipal Water District 

220 Nellen Ave. 

Corte Madera, Ca. 94925 

(415) 945-1551 

lgrabow@marinwater.org 

Erik Grijolva, Peggy Olofson, Katy Zaremba 

Coastal Conservancy Invasive Spartina Project 

(510) 681-5371 

ISPOlofson@aol.com, kzaremba@scc.ca.gov 

Dan Hamon 

USDA-APHIS 

(916) 857-6260 
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Dave Hardt 

USFWS Kern NWR 

Kern National Wildlife Refuge Complex 

P.O. Box 670 

Delano, CA 93216-0670 

(661) 725-2767 

dave_hardt@r1.fws.gov 

Jim Husting 

Golf Course Vegetation Manager 

Woodbridge, CA 

(209) 368-9040 

jchust@softcom.net 

Jeff Janik 

California Department of Water Resources 

jjanik@water.ca.gov 

Tom Jordan 

Harbor Bay Homeowner's Association 

(510) 865-3363 

Troy Kellet 

Richvale Irrigation District Manager 

P.O. Box 147 

Richvale CA 95974 

(530) 882-4243 

Dr. Robert Leavitt 

California Department of Food and Agriculture 

1220 N Street, Sacramento, CA 95814 

(916) 654-0768 

rleavitt@cdfa.ca.gov 

Chuck Locher 

Turlock Water District 

333 E. Canal Dr. 

Turlock, California 95380 

(209) 883-8300 

Dr. Karl Malamud-Roam 

Environmental Projects Manager 

Contra Costa Mosquito and Vector Control District 

155 Mason Circle 

Concord, CA 94520 
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(925) 685-9301 x107 

Florence Maly 

California Department of Food and Agriculture 

1220 N Street 

Sacramento, California 95814 

Gene Martin 

Big Bear Municipal Water District 

P.O. Box 2863 

40524 Lakeview Dr. 

(909) 866-5796 

gmartin@bbmwd.org 

Tom McNabb 

Clean Lakes, Inc. 

P.O. Box 3186 

Martinez, CA 94553 

(925) 957 1905 

info@cleanlake.com 

Mike Mizumoto 

Imperial Irrigation District 

(760) 339-0565 

mrmizumoto@iid.com 

Marty Muschinske 

California Department of Fish and Game 

(619) 468-3064 

mmuschin@dfg2.ca.gov 

Dave Najera 

Aquatic Environments, Inc. 

(510) 406-0784 

davenajera@hotmail.com 

Ross O'Connell 

California Department of Food and Agriculture 

1220 N Street, Sacramento, California, U.S.A. 95814 

(916) 654-0768 

roconnel@cdfa.ca.gov 

Dave Omoto 

Contra Costa Water District 

1331 Concord Ave. 

Concord, CA 94524 
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925-688-8023 

domoto@ccwater.com 

Pat Panus 

Contra Costa Water District 

1331 Concord Avenue. P.O. Box H2O 

Concord, CA 94524 

(925) 688-8090 

Jeff Pasek 

Water District of San Diego 

City of San Diego 

Water Production Div., Water Quality Lab 

5530 Kiowa Drive 

La Mesa, CA 91942 

619-668-3240 

jpasek@sandiego.gov 

Bill Paznokas 

CDFG S. Coast Region 

(858) 467-4218 

Jane Sooby 

Organic Farming Research Foundation 

P.O. Box 440 

Santa Cruz, CA 95061 

831-426-6606 

jane@ofrf.org 

Dr. David Spencer 

USDA Agricultural Research Station 

(530) 752-1096 

dfspencer@ucdavis.edu 

Jeff Stuart 

National Oceanic & Atmospheric Administration 

National Marine Fisheries Service 

Protected Resources Division 

650 Capitol Mall, Suite 8-300 

Sacramento, CA 95814-4706 

(916) 930-3607 

j.stuart@noaa.gov 

Brian Sullivan 

Golf Course Vegetation Manager 

Bel Air Country Club 
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Thousand Oaks, CA 

(310) 440-2428 

Dr. Bill Taylor 

Metropolitan Water District of Southern California 

700 Moreno Avenue 

La Verne, CA 91750 

(909) 392-5149 

wtaylor@mwdh2o.com 

Greg Tischler 

Tahoe Keys Property Owners Association 

356 Ala Wai Blvd. 

South Lake Tahoe, CA 96150 

(530) 542-6444 

Mark Vale 

Solano Irrigation District 

(707) 448-6847 ext. 40 

Mark Wander 

Santa Clara Valley Water District 

5750 Almaden Expressway 

San Jose, CA 95118-3686 

mwander@valleywater.org 

Bob Weber 

Reclamation District 999 

(916) 775-2144 

recdist999@sprintmail.com 

Frank Zarate 

California Department of Food and Agriculture 

(559) 445-5031 

Out of State Practitioners

Jonathan Bates 

Willopa National Wildlife Refuge 

360-484-3482 

Washington 

Dr. John Barko 

Waterways Experiment Station, USACE 
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Vicksburg, Mississippi 

(601) 634-3654 

Ann Bove 

Vermont DEC 

Vermont Department of Environmental Conservation 

Water Quality Division 

103 South Main Street 

Building 10 North Waterbury, Vermont 05671-0408 

(802) 241-3782 

annbo@dec.anr.state.vt.us 

Dr. Raghavan Charudattan 

Professor, Plant Pathology Department 

PO Box 110680 

University of Florida 

Gainesville, FL 32611-0680 

TEL: 352-392-3631, ext: 354 

FAX: 352-392-6532 

EMAIL: rc@ifas.ufl.edu 

Wayne Corban 

St. John’s River Water Management 

386-329-4276 

wcorban@sjrwmd.com 

Florida 

Dr. Al Cofrancesco 

Waterways Experiment Station, USACE 

Vicksburg, Mississippi 

cofrana@wes.army.mil 

Dr. Lee DeHaan 

The Land Institute 

2440 E. Water Wells Road 

Salina, Kansas 67401 

785-823-5376 

theland@landinstitute.org 

Dr. Bill Haller 

Institute for Food and Agricultural Sciences 

University of Florida 

352-392-9615 

wth@mail.ifas.ufl.edu 

Kathy Hamel 
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Aquatic Plant Specialist 

Washington Department of Ecology 

360-407-6562 

Daniel Helsel 

Wisconsin Department of Natural Resources 

Water Program Supervisor 

Black-Buffalo-Trempealeau River Basins 

910 Hwy 54, Black River Falls, WI 54615 

715-284-1431 

Daniel.Helsel@dnr.state.wi.us 

Bret Henninger 

Resource Quality Department 

513-728-3551 ext. 265 

www.greatparks.org

Ohio 

Martin Hilovsky 

President 

EnviroScience, Inc. 

3781 Darrow Road 

Stow, Ohio 44224 

(800) 940-4025 

www.enviroscienceinc.com

Jill Hoffmannn 

Aquatic Biologist 

Lake and River Enhancement Program 

IDNR - Division of Soil Conservation 

Indianapolis, Indiana 

(317) 233-5468 

Vanessa Howard 

Center for Lakes and Reservoirs 

Portland State University 

Portland, Oregon 

(503) 725-9076 

vhoward@pdx.edu 

Marleen Kromer 

Director of Interagency Program Development 

The Nature Conservancy – Ohio Chapter 

6375 Riverside Drive 

Dublin, Ohio 43017 

614-717-2770 
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mkromer@tnc.org 

Dr. Richard C. Lathrop 

Aquatic Community Ecologist 

Wisconsin Department of Natural Resources 

c/o UW Center for Limnology 

Madison, WI 53706 

Telephone (608)-261-7593; fax (608)-265-2340 

email: rlathrop@facstaff.wisc.edu 

Judy Ludlow 

Bureau of Invasive Plant Management 

850-245-2816 

Florida 

Dr. John Madsen 

Mississippi State Georesources Institute 

ERC, Rm 225 

Box 9652 

Mississippi State University, MS 39762 

(662) 325-2428 

Terry McNabb 

AquaTechnex 

P.O. Box 118 

Centralia, WA 98531 

(360) 330-0152 

Fax: (360) 330-0174 

Nancy J. Mueller 

New York State Federation of Lake Associations 

fola@nysfola.org 

Hilary Oles 

Adirondack Park Invasive Plant Program 

c/o Adirondack Nature Conservancy 

P.O. Box 65 

Keene Valley, New York 12943 

518-576-2082 x 131 

holes@tnc.org 

Fritzi Olson 

Adopt a River 

PO Box 357098 

Gainesville, Florida 32635 

352-264-6827 
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aar@currentproblems.org 

Sheilpa Patel 

Florida Orange Port 

President of Dredging and Marine Consultants 

spatel@dmces.com 

(386) 304-6505 

David Penny 

Masters Dredging, Inc. 

Kansas 

(913) 583-3335 

Dr. Judy Shearer 

Waterways Experiment Station, USACE 

Vicksburg, Mississippi 

shearej@wes.army.mil 

(601) 634-2516 

Hannah Spaul 

The Nature Conservancy – Wisconsin Field Office 

Madison Field Office 

633 West Main Street 

Madison, WI 53703 

(608) 251-8140 

wisconsin@tnc.org 

Dr. Mark Sytsma 

Portland State University 

Portland, Oregon 

www.clr.pdx.edu 

(503) 725-3833 

Dean Wong 

New York State Federation of Lake Associations 

(518) 587-8100 ext.219 
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APPENDIX C: FEASIBILITY SCREENING FOR DIFFERENT 

WEED CONTROL METHODS 

This Appendix develops practical recommendations, based on best available 

science, for what control methods may be appropriate in different plant management 

scenarios. The focus of the Appendix is on alternative methods used to control aquatic 

weeds. The end-users of this information will include the California State Water Quality 

Control Board, special interest groups, and the various state, local, and private agencies 

that control aquatic plants. This Appendix is not an evaluation of all potential aquatic pest 

control methods presented in the main body of the report. Rather, it provides a general 

starting point for practitioners having little experience with aquatic plant control methods, 

to decide if some of the most commonly used methods are appropriate for their 

management circumstances. This information may also be a useful reference in permit 

preparation, as it summarizes the recommendations of local experts regarding what 

methods may or may not be appropriate in various management scenarios. 

This Appendix presents tables indicating what non-chemical control methods may 

work for plant management scenarios that are common in California. Once a manager has 

identified a water body type and plant problem to control, they may use these tables to 

quickly determine potential control methods. The tables provide information on 

feasibility of the methods, expected control costs, and permitting requirements. These 

tables were developed based on the recommendations of the aquatic plant scientists and 

managers from the Non-Chemical Alternatives Environmental Economic Workgroup, 

interviews with field practitioners in the state, and reviews of the scientific and 

management literature on these plant control methods. 

Table 1 depicts an initial screening of plant control methods, to determine which 

ones are likely to be feasible for a given water body and plant type (the methods are 

described in much greater detail in the main body of the report). Numbered cells indicate 

significant limitations that may make a particular method unfeasible in a particular 

management scenario. Table 2 presents narrative information about the limitations of the 

particular methods. As with Table 1, this information is organized according to water 

body type and plant type. Additionally, environmental hazards associated with the 
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methods are presented, as well as other potential limitations. Both tables should be 

considered in creating an initial listing of potential methods. 

Table 3 indicates the permitting requirements of the different control methods. 

Permits that may be required include Section 404 permits, Section 401 permits, 1600 

permits, and NPDES permits. Several other types of permits are only required for one 

type of method, as presented in the table. Several permitting requirements may be 

addressed by filing a Joint Aquatic Resource Permit Application (JARPA). 

The Army Corps of Engineers (USACE) requires a Section 404 permit if large 

volumes of soil, sediment, or vegetation are discharged into “waters of the United 

States”. Waters of the United States are defined as any water body connected to U.S. 

navigable waters. Whether the discharge is of sufficient scale to require a permit is 

somewhat subjective, but permits are typically required for operations that discharge 

more than 750 cubic yards of material. The California Regional Water Quality Control 

Boards (RWQCB) administers Section 401 permits, which are required for certain 

activities that affect water quality (these are also referred to as CEQA permits). For 

practices possibly requiring Section 401 permits, an inquiry should be made with the 

RWQCB office. California Department of Fish and Game require “1600 Lake and 

Streambed Alteration Permits” for practices that may damage benthic habitat. NPDES 

permits are required for all chemical control methods that result in discharge of 

chemicals into “waters of the United States”. 

Additionally, many control methods may require that a Biological Assessment be

submitted to USFWS and/or NMFS, who will then prepare a formal Biological Opinion.

A formal review by these agencies will be required if there is the possibility that federally 

endangered or threatened species will be harmed or killed, or their habitat degraded, by 

the control methods. This pertains to locations where USFWS or NOAA/NMFS has 

identified habitat for listed species. The USFWS/NMFS reviews can take upwards of a 

year or more, particularly for projects that are not conducted in collaboration with a 

federal organization. 

Table 4 presents general cost information on the implementation of the methods. 

This table can be usable to generate some “back of the envelope” cost calculations for the 
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methods. Managers wanting guidance on how to perform a more detailed cost 

effectiveness analysis for their particular management scenario should consult the report 

prepared by Mann (2003). 

With many aquatic weed species, the risk of further spreading of the infestation 

should also be considered in control method selection. This is particularly important for 

species that readily spread by fragmentation. Although it is difficult to exactly quantify 

the risk that a particular control method will cause new infestations to develop, Table 5 

qualitatively compares the relative risk among control methods and plant species. It 

should be noted that the risk of control methods spreading infestations within or among 

water bodies is an area where future scientific research is needed. 

Several aspects of the water body are important in determining whether further 

spread is a concern. Spreading poses a much greater risk in water bodies with outlets 

flowing into other water bodies. Also, great caution should be exercised in controlling 

new infestations or infestations that have not taken over the entire water body. For 

example, CDFA’s hydrilla eradication program on Clear Lake does not permit methods 

that spread fragments in areas adjacent to hydrilla infestations (CDFA 2003a). In 

contrast, closed systems that are completely taken over by an infestation do not pose a 

significant risk for further spread. In these systems, method selection may be more driven 

by other factors, such as the method that is likely to provide immediate relief from the 

infestation. 

For methods listed as high risk in Table 5, specific management practices may be 

conducted to mitigate the risk of infestation spreading. For example, booms, curtains, 

nets, or other structures may be set up in the water bodies to keep fragments from 

spreading. 

There is a trade-off in presenting these tables; by condensing a wide variety of 

management recommendations into a short space, many subtleties are overlooked. Please 

refer to the main body of the report to address these subtleties. Tables 1 and 2 should be 

viewed only as practical screening devices for identifying methods that may be effective 

for a given management problem. Table 3 should be used as an indicator of what 

agencies should be contacted to evaluate whether their permits will be required. 
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Table 1. Look-up table for feasibility of aquatic plant management practices by water body and plant type.

Water Body Type Common Weed Species Plant Type

Practice 

Delta 

Small Lake 

Large Reservoir 

Irrigation Canal 

Stormwater Canal 

Wildlife Refuge 

Estuarine Wetland 

Eurasian watermilfoil 

Hydrilla 

Water hyacinth 

Pondweed 

Egeria densa 

Spartina

Cattail/Tule 

General Emergent 

General Floating 

Harvesting 5 4,5 5Cutting 5 4,5 5Excavation 1 1 2Manual Removal*Bottom Barriers* 6 6 6 6 2Rotovation 5 4,5 2 5 2Water Drawdown 1 6 5 5 5 3 3 2Sterile Grass Carp 4, 8 3,8 4 3,8 7 7 3,

6,7

3,6,7 2,3,6,7

Insect 3 7 7 7 7 7Chemical Controls Cells containing footnotes may not be feasible because of reasons listed below.

*Method works best on small infestations

1 – Likely to be very costly and logistically difficult 2 – Unlikely to be effective

3 – Feasibility unknown; never tried in CA waters 4 – Illegal or possibly illegal in CA

5 – May enhance species or spread infestation 6 – Rapid water flow or estuary conditions may interfere

7 – Not a preferred food item 8 – Fish escape or mortality likely

9 – Effective biological control agent not available
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Table 2. List of Aquatic Plant Management Practices And Limitations

Practice Description Restrictions by Type

of Water Body

Restrictions by Type

of Plant

Environmental

Restrictions

No Practice No intentional actions to

reduce aquatic plants

Plant impacts on the

ecosystem and the

environment may beunacceptable

Harvesting Cut, harvest and

disposal

Potential for fragment

release is worse in

flowing water

May spread infestation

for milfoil, hydrilla,

egeria, or other species

that spread by

fragmentation

Will remove aquatic

animals (e.g., juvenile

fish), particularly in

dense vegetation

Cutting Cut aquatic weeds Potential for fragment

release is worse in

flowing water

Likely to spread

infestation for milfoil,

hydrilla, egeria, or other

species that spread by

fragmentation

May add excess

nutrients to water

column and cause

dissolved oxygen

reduction

Excavation Remove sediments and

overlying plants.

Methods includerotovation, chaining,

suction dredging,

backhoe with rake

Generally require easy

shoreline access for cost

effectiveness; preferable

in dewatered systems

Turbidity and

contaminant flux. May

spread infestation

downstream

Manual Removal Individuals "weed"

bottoms, may require

divers

Bottom Barriers Semi-permanent

materials laid over plant

beds

Difficult to maintain in

flowing or tidally

influenced waters

Not usually effective for

floating or emergent

plants

Could affect benthichabitat
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Table 2. Continued. List of Aquatic Plant Management Practices and Limitations

Practice Description Restrictions by Type

of Water Body

Restrictions by Type

of Plant

Environmental

Restrictions

Rotovation Submerged aquatic

rototilling

Water must be at least

6” - 8” deep, but not too

deep

Will not work for

floating plants

May contribute to

turbidity and

contaminant flux

Water Level Drawdown Dewater system to kill

plants

Must have water control

structures

Some species enhanced

by drawdown

Sterile Grass Carp Stock juvenile carp Eurasian watermilfoil,

parrotfeather, and water

hyacinth not preferred

foods

Can switch lake from

macrophyte dominated

to algae dominated. Not

permitted in waters that

outflow to other natural

waters

Insect Introduce insects that

specialize in consuming

target plants

Population

establishment more

difficult in flowing

waters

Currently available in

CA for purple

loosestrife and water

hyacinth.

Insects have

substantially controlledalligatorweed in coastal

states from Virginia to

Texas.

Pathogens or predators

in system may reduce

biological control agent

population
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Table 3. Permitting Requirements For Aquatic Plant Management Practices (not definitive)

Practice Permits That May Be Required

General USFWS or NMFS formal Biological Opinion may be requiredHarvesting RWQCB Section 401Cutting RWQCB Section 401Sediment Excavation CDFG 1600; RWQCB Section 401; USACE Section 404Hand pull Certification required if SCUBA used.Bottom Barriers CDFG 1600Rotovation CDFG 1600; USACE Section 404; RWQCB Section 401Water Level Drawdown RWQCB Section 401; CDFG Permit to kill fish, if drawdown will cause

mortality in natural waters

Sterile Grass Carp RWQCB Section 401; CDFG Stocking Permit; Method only permitted when not

contiguous with other California waters or in FEMA defined 100 year

floodplain; not permitted in water bodies containing endangered species.

InsectChemical Control NPDES permits; RWQCB Section 401; applicator must be licensed by DPR
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Table 4. Estimated Costs for Various Aquatic Plant Control Methods.

Non-Chemical Control Cost Estimates per

Acre in U.S. Dollars

Number of

Treatments per

Growing Season

References

Grass Carp 45 - 125 1

Washington State

Department of Ecology

2001

Mechanical Harvesting

500 - 900

2 – 6

(2 – 3 for submersed,

3 – 6 for floatingplants)

Washington State

Department of Ecology

2001

Rotovation 1,200 – 1,700 1 - 2 Taylor and Gately 1998Diver Dredging 1,100 – 2,000 1 - 2 Taylor and Gately 1998Bottom Barriers 14,000 – 26,200 0.5 Taylor and Gately 1998Mechanical Cutting 100 – 11,000 10 - 12

Washington State

Department of Ecology

2001

Weed Rollers 2,000 10 - 30 Washington State

Department of Ecology

2001

Manual Pulling 500 – 2,400 1 Gibbons et al. 1994

Note: A range of different environmental conditions and different contract agreements apply for all of the above methods.
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Table 5. Relative Risk That Aquatic Plant Management Practices Will Cause an Infestation to 

Spread to New Locations. 

H = high risk of infestation spreading; M = medium risk; L = relatively low risk. N/A = Method not 

appropriate for that species for other reasons. 

Practice 

E

urasian

watermilfoil

Parrotfeather

H

y

drilla

Egeria densa

Salvinia molestaWater h

yacinth

Cattail/T

ule

S

partina

Pon

d

weed

Mechanical Cutting* H H H H H M M H H 

Mechanical Harvesting* H H H H H M M M M 

Rotovation * H H H H N/A N/A H H H 

Sediment Excavation M M M M N/A N/A L1 L1 L1 

Grass Carp** L L L L N/A L N/A N/A L 

Hand Pulling L L L L L L L1 L2 L 

Bottom Barrier L L L L N/A N/A L L L 

Insects N/A N/A N/A N/A L L N/A N/A N/A 

Chemical Treatment L L L L L L L L L 

*Specific management practices may reduce potential of spreading (e.g., booms, curtains) 

**Grass carp is an introduced species that may not be used when spread between water bodies is likely. 

L1Assumes complete removal of cut/harvested material. 

L2 Only seedling, or very young Spartina is feasible to remove by hand. 
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APPENDIX D: PEER REVIEW 

The following peer review of this report was provided by Dr. John Madsen, Faculty 

Member, Mississippi State University. Dr. Madson is the author of many aquatic plant 

management publications, including ”Advantages and disadvantages of aquatic plant 

management techniques,” LakeLine 20(1): 22-34. Available at 

http://www.aquatics.org/pubs/madsen2.htm. This document has been revised in April, 

2004, in response to the comments of this peer review. 

Review of Report: 

“Review of Alternative Aquatic Pest Control Methods for California Waters” 

Written by San Francisco Estuary Institute 

Reviewed by John Madsen, 2 March 2004 

General Comments: 

1. The review of alternative management techniques was complete in both breadth and 

depth, without being encyclopedic. I think the discussion of each technique was objective 

and balanced. I have made numerous specific points below, but I think that these points 

are, on the whole, minor. 

My main comment is a caution in terms of how this review is used. For managing 

invasive aquatic plants we need all the tools at our disposal, without unnecessarily 

restricting our selection. To eliminate one set of tools, herbicides, from our arsenal would 

be as foolhardy as to use this tool in a completely indiscriminate manner. The exact 

balance between chemical and nonchemical methods is one determined by the species 

managed, the ecological system, and other factors. The main problem is the invasive 

plant species, not the management. Invasive species are the second leading cause of 

species extinction and reduction of species diversity, as well as having other negative 

impacts on ecosystems. 

In particular, herbicides are the single best tool for managing intermediate to large dense 

infestations. While significant progress can be made with a number of difference 

techniques on small infestations, the use of alternative techniques becomes progressively 

more difficult as the infestations grow in size. 

Eliminating herbicides from management planning may only serve to unnecessarily 

increase the cost of managing invasive plants, or allow infestations to grow in size 

unchecked to the point where available tools or resources are not capable of managing the 

population. Often, these are resources that might be better placed in mitigating nontarget 

impacts of management. 
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If we sit back and reconsider how we are managing invasive species, without continuing 

our management activity, the invasive species will not observe our moratorium. They will 

continue to grow, developing a larger problem once we decide to address the issue once 

more. 

2. I sensed a general willingness to introduce exotic animals (insects, snails, etc.) to 

control exotic plants, in lieu of using synthetic pesticides. I think that, while it is a value 

judgment whether the risk of new exotic infestations is more significant than the risk 

from synthetic pesticides in the environment, the potential for these exotic biocontrol 

agents to then become a problem has not been addressed. Aquatic pesticides, to be 

labeled for use in the US, must have no evidence of biomagnification, must break down 

and dissipate in the environment, and have a short half- life. A biocontrol agent, to be 

effective, must biomagnify (e.g., reproduce), ha ve a long and increasing half- life, and 

not dissipate in the environment but in fact persist. As an ecologist, this concerns me. 

John Magnuson aptly put it in 1976, that managing exotics with exotics is playing with 

fire. 

Specific Comments: 

1. Literature review, pg. 5. You did not specifically cite the Aquatic Plant Information 

Retrieval Service (APIRS) at the University of Florida. They are a particularly good 

source of information on gray literature regarding aquatic plant management, at 

http://plants.ifas.ufl.edu/search80/NetAns2/.

2. Practitioner Survey, page 5. I commend you for interviewing practitioners – they are 

an important source of information that is often overlooked. 

3. Fish Biomanipulation, Page 10. Fish biomanipulation only works on planktonic algae, 

and has generally been most successful in small lakes when combined with nutrient input 

control. In addition, most lakes have only had successful water quality improvement 

(e.g., reduction in algal growth) for a few years after manipulation. Fish manipulation 

usually results in an increase in the growth of submersed plants. Fish biomanipulation 

works best in shallow lakes when top predator fish are increased AND omnivorous, 

benthivorous fish (e.g., carp) are controlled. 

4. Insect biocontrol, pg. 12. It is highly debatable how effective insect biocontrol has 

been for waterhyacinth in Florida. Florida State DEP officials put so little stock in its 

effectiveness that they have continued their management program of maintenance 

management with herbicides on small populations of waterhyacinth. While some 

researchers contend that biocontrol on waterhyacinth reduces plant height and flowering, 

they concede it does little to prevent the expansion of the mat. 

The hydrilla flies have shown even less propensity to control hydrilla in the field, though 

sporadic declines of hydrilla have been noted in the presence of the hydrilla flies. This 

contrasts with the hugely successful use of the alligatorweed flea beetle to control 

alligatorweed, which rapidly reduced the aquatic infestations of this pest throughout 
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much of its range (though not its terrestrial or wetland growth). Other biocontrol projects 

with purple loosestrife and melaleuca have likewise shown demonstrable results. 

All of the projects above are examples of the classical approach to biocontrol, in which 

insects that feed on the target plant are found in the overseas native habitat and, after a 

long series of studies, released into the wild in the US. Eurasian watermilfoil biocontrol is 

completely different. The naturalized milfoil weevil was found to feed on Eurasian 

watermilfoil, but also feeds on the native northern watermilfoil, but with less damage. By 

serendipity, the milfoil weevil can cause declines of Eurasian watermilfoil under 

laboratory, experimental field, and natural field conditions. However, there is no 

guarantee that these high populations of weevils are sustainable. Simply put, there is no 

theoretical basis for believing that release of the milfoil weevil alone with suppress 

Eurasian watermilfoil populations, and no operational plan for their use has been

implemented. The only way to make the weevils work predictably is to perform 

augmentive releases from reared populations, a prospect that is prohibitively expensive. 

5. Organic Material Amendment, page 17. While some organic additions may reduce 

algal growth and some rooted plants, they may actually increase the growth of 

waterhyacinth and other free-floating plants, which prefer acidic water for nutrient 

uptake. 

6. Acetic Acid, page 18. Acetic acid is effective on waterhyacinth, but has not been 

approved for use in aquatic environments by the US EPA as a pesticide, and is unlikely to 

receive this approval. Likewise, application of acetic acid to aquatic vegetation will 

increase acidity of surface waters and impact aquatic life. While it may be effective for 

floating vegetation, I predict that the impact on aquatic life will be far more than 

conventional herbicides. 

7. Plant Competition, page 19. I have done a number of plant competition or native plant 

revegetation experiments. Invariably, the nuisance plant must first be controlled, and then 

the native plant added. Native plant revegetation is less a control technique itself than a 

remediation to prolong the effectiveness of control – and even at that, it does not always 

work as intended. 

8. Mechanical Harvesting, page 22. The main problem with mechanical harvesting is that 

it is relatively slow; a single harvester may only be able to cut 1 to 4 acres per day. 

Mechanical harvesting of large infestations is therefore problematic, requiring a large 

number of harvesters. 

The ability of harvesting to remove nutrients from lakes has been dramatically overstated. 

Carpenter’s calculations, while correct, assume that one harvests all of the plants in the 

littoral zone – an unlikely scenario. The amount of nutrients removed by a typical 

management program is usually far less than internal loading rates, much less external 

inputs to the lake. 
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9. Mechanical Cutting, page 24. One overlooked aspect of cutting is that it is 

demonstrably faster than harvesting, thus allowing the same area to be treated by fewer 

machines than harvesting. 

10. Rotovation, page 26. Rotovation creates a lot of turbidity, resuspends nutrients from 

the sediment, and produces large numbers of fragments that may spread target species, 

even if a harvester is attempting to collect fragments. 

11. Weed Rollers, page 27. The State of Minnesota (DNR) requires permitting of weed 

rollers and limits their size and location to reduce impacts on littoral habitats. They are 

particularly concerned about the use of weed rollers on sediments high in organic matter. 

12. Manual Removal, page 31. Manual removal seems to work best when occasional 

scattered plants are the target, rather than dense growths of plants. Particularly with

submersed plants, once the first plant is pulled, visibility drops to almost nothing and 

companion plants are difficult to locate and remove. 

13. Non-conventional Chemical Controls, page 38. One overlooked problem with 

nonconventional chemical controls is that US EPA has approved none of these chemicals 

for use in aquatic environments as pesticides, with the exception of Aquashade. The 

effects of many of these chemical treatments on aquatic life are virtually unknown. While 

many of these chemicals are widely used on pelagic algal growth, with generally 

predictable results, their use in the littoral zone for control of rooted or free- floating 

vascular plants are largely experimental or untested. 

14. Relative Reliance, page 44. While I agree that some natural resource and regulatory 

agencies are attempting to manage invasive aquatic plants, notably Eurasian watermilfoil, 

using alternative methods exclusively, in Lake George they are losing that battle. 

Alternative methods work best if the infestation is managed as soon as possible, and on 

populations before they reach dense beds of greater than 1 acre. Once dense beds are 

formed, it is difficult if not impossible to control them with available appropriate 

alternative techniques. 

Vermont recently approved the use of fluridone to control Eurasian watermilfoil, with 

considerable success. The number of applications and pressure to follow this up with 

additional treatments in other lakes was significant. 

15. Preventive Measures, page 47. I heartily concur that any aquatic plant management 

program should include an element of prevention – both to prevent the spread of the 

target plant to other waters, and to prevent the introduction of new invaders to the waters 

being managed. 

16. Mix of techniques, page 47. I would concur that any aquatic plant management 

program should have a mix of manage ment techniques, including both chemical and 

nonchemical techniques. Preferably, nonchemical techniques would predominate when 

target invasive plant populations would reach small numbers and density. Likewise, any 
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management effort focusing on reducing the growth of planktonic algae must include 

reducing the source of nutrients in the watershed. With nuisance rooted and floating 

plants the problem, however, is not the management technique itself, but all-too-often is 

the results of an introduction of no nnative aquatic vascular plants. 

17. Page 49. Recheck the citation for Caffrey et al. 1996. I suspect that this is an article 

authored by either Boylen or Eichler, in a volume edited by Caffrey et al. 

18. Page 55. Madsen 1997 was cited in the text, but is not listed in the literature cited 

section.

19. Appendix 3, Table 2, page 82, No practice. The “no management option” overlooks 

the impact of the nonnative aquatic plant invader on the ecosystem and environment that, 

in some cases, can be significant. 

20. Appendix 3, Table 2, Page 83, Insect. Insects may be available for waterhyacinth in 

California, but they won’t make much difference to the problem growth of waterhyacinth 

in the Delta. You could add insects have substantially controlled alligatorweed. 

21. Appendix 3, Table 4, Page 85, Mechanical Cutting. I think 10-14 cuts per year are 

pretty excessive for mechanical cutting of submersed plants and, even, emergent plants. I 

don’t see why cutting would be an order of magnitude higher than harvesting, which is 

essentially the same thing except that the cut material is collected. This might need 

clarification. 

22. Appendix 3, Table 4, Page 85, Mechanical harvesting. I think 1-2 cuts per year is on 

the low side for submersed plants (in California), and well below what would be needed 

for emergent and floating plants – a better estimate would be 2 to 6 (2 to 3 for submersed, 

3 to 6 for floating plants). 

Completeness of Report: 

The report on alternative pest control methods for California waters produced by the San 

Francisco Estuary Institute is thorough in both breadth (options discussed) and depth, 

without being unnecessarily verbose or encyclopedic. The most likely and applicable 

alternative technologies are discussed, a significant proportion of the scientific literature 

(both peer-reviewed and agency reports) is reviewed, and a relatively balanced view 

presented.