Those who cannot remember the past are condemned to repeat it. George Santayana - American Philosopher, Poet

Introduction

Major aquatic weed problems in the United States began in about 1850.Prior to 1940, the management of aquatic plant problems in public waters was the responsibility of three federal agencies: The U.S. Army Corps of Engineers, the Bureau of Reclamation and the U.S. Fish and Wildlife Service. While each agency had unique problems, they dealt primarily with aquatic plants like cattails (Typha spp.), reeds (Phragmites spp.), alligator-weed (Alternanthera philoxeroides), water hyacinth (Eichhornia crassipes), and water-chestnut (Trapa natans).

The U.S. Army Corps of Engineers is responsible for maintaining the nation's navigable waterways. The Corps of Engineers became involved in the management of aquatic plants before 1900 primarily because excessive growths of water hyacinth and alligator-weed clogged many of the South's navigable waterways; waterways that were essential to early commerce and development in the region. The River and Harbor Act of 1899 authorized the U.S. Corps of Engineers to begin major aquatic plant control programs throughout the South. The U.S. Corps of Engineers based their early aquatic weed control program on the use of man-power and mechanical devices. The Corps started with drag lines and derricks designed to remove aquatic vegetation from structures (e.g., dams, locks, spillways) where plants accumulated as a result of water flow. Shore-based conveyer systems were then developed to remove vegetation with a shift to barge-mounted conveyers for work in rivers and large lake systems.

Crusher boats were used for a short time for the control of water hyacinth. On these boats, water hyacinth plants were lifted from the water and pressed through heavy rollers to crush and destroy the vegetation before discharging it back into the waterway. The saw boat or "destroyer barge" was one of the more effective boat mounted machines for use in rivers. These boats had sets of saw blades spaced about 1 inch apart mounted on a high speed rotating shaft to shred plants into an aquatic soup. This was an efficient method of immediately opening a clogged waterway. Saw boats had an operational range of up to 8 acres per day and less than 5% of the water hyacinths cut by the blades recovered and resumed growth. Water hyacinths, however, grew rapidly and soon closed the newly opened waterways.

Although an engineering or construction attitude encouraged the Corps of Engineers to develop mechanical solutions for weed control problems, the Corps of Engineers experimented with drawdown, water manipulation and large-scale chemical treatments. Drawdowns and water level manipulation were not particularly effective for the control of alligator-weed and water hyacinth in southern waters, but were effective in northern latitudes where freezing conditions effectively killed plant roots in drawdown areas. Early herbicides were limited to inorganic contact materials such as sodium arsenite, sodium chlorate, and copper sulfate. Although chemical treatments with sodium arsenite were effective, safety hazards associated with using sodium arsenite ultimately led to prohibiting the use of any chemical harmful to fish and cattle.

The Bureau of Reclamation of the United States Department of Interior has responsibility for developing irrigation systems in the arid and semi-arid west. A major problem for the Bureau of Reclamation is keeping thousands of miles of irrigation and drainage canals and their banks free of weeds that can interfere with water movement. Aquatic weed problems, however, followed the arrival of water in each developing irrigation district. Prior to 1940, the Bureau dealt primarily with two types of weed problems, submersed weeds in the canals and emergent species in the drains. The major submersed weeds were pondweeds and the major emergent weeds were cattails and tules (Scirpus spp.). Willows (Salix spp.) and tamarisk (Tamarix spp.) also caused problems along ditch banks.

The Bureau of Reclamation's early aquatic weed control programs, like those of the U.S. Army Corps of Engineers, were based on the use of man-power and mechanical devices. The Bureau used railroad rails, discs, harrows, binderwheels and chains. These devices were dragged up and down laterals and canals in an effort to dislodge weeds. The Bureau, however, encountered numerous problems with mechanical control. Mechanical control required large numbers of workers and the lack of access roads forced some irrigation districts to periodically use expensive methods of hand scything (physically using a tool with a long, single blade on a bent wooden handle that was used to cut grains in agricultural practices) to cut weeds from canals.

The Bureau of Reclamation also experimented with chemical control and water level manipulation. Chemical control with inorganic compounds was not particularly effective in flowing water systems and great caution was required when treating irrigation water. Drying out lateral canals was an effective method of weed control, but it could take up to 5 days to complete drying and kill submersed vegetation. This was not a popular method of weed control with farmers who depended upon irrigation water for their crops, but desperate conditions called for desperate measures.

The U.S. Fish and Wildlife Service of the U.S. Department of Interior is responsible for establishing and maintaining both coastal and interior wetlands for waterfowl habitat. The Fish and Wildlife Service became involved in the effort to manage aquatic weed problems when public interest in the restoration of waterfowl increased in the early part of the 20th century. The U.S. Fish and Wildlife Service initiated weed control programs to encourage establishment and spread of desirable duck food plants.

Plant species, such as pondweeds (Potamogeton spp.) and bulrush (Scirpus spp.), were considered by the U.S. Fish and Wildlife Service as highly desirable native plants. The primary aquatic weed species for the Fish and Wildlife Service were alligator-weed, water hyacinth, phragmites, and cattails, which were considered undesirable invaders and subjected to large-scale control operations. Fish and Wildlife Service employees used fire, water manipulation (flooding and drawdown), and mechanical equipment for weed control.

The development of objectionable marsh weeds and destruction of desirable species was linked by U.S. Fish and Wildlife researchers to alternate wet and dry cycles that favored the introduction and establishment of undesirable species. Prior to 1945, the U.S. Fish and Wildlife Service relied extensively on water level management to reduce growth of certain aquatic weed species. Dikes and small dams were used to raise water levels to a permanent depth of at least 3.5 ft (1.1 m) to eliminate alternate wet and dry periods. The Service, however, recognized the value of combination treatments for more predictable control. Mechanical control, including hand-pulling and underwater mowing, was used extensively. Methods developed by the Corps of Engineers were also used for crushing aquatic vegetation.

The U.S. Fish and Wildlife Service in its early efforts to control undesirable growths of aquatic weeds experimented with biological control and chemical control. The Service, in order to control submersed plants used fertilization to produce planktonic algae blooms to reduce light penetration. European or common carp (Cyprinus carpio) were also used to reduce light penetration because carp muddied the water during bottom feeding. Carp, however, also destroyed plants by uprooting vegetation during feeding. Inorganic herbicides were used, but only on limited basis or in small areas. Mechanical manipulations became favored over biological and chemical control methods by the U.S. Fish and Wildlife Service because weeds were usually interspersed with desirable species and both were controlled by the non-selective herbicides and biological controls available at the time.

The U.S. Army Corps of Engineers, the Bureau of Reclamation, and the U.S. Fish and Wildlife Service had by 1945 brought the "state of the art" of weed control methods, other than herbicides, to a higher efficiency. The three agencies, however, recognized that mechanical weed control methods had reached their economic limitations. Individual states, usually through state game and fisheries agencies, kept abreast of operations by the federal agencies and also utilized similar methods of aquatic weed control. However, unless newer and less expensive methods became available, aquatic plant management operations would be severely restricted at a period when utilization of waterways was increasing and introduced weeds were spreading rapidly.

The U.S. Department of Agriculture (USDA) assumed the role of lead agency in aquatic weed research when funding became available for weed science in the late 1940s. Cooperative arrangements were established with the Corps of Engineers and the Bureau of Reclamation as part of the federal government's efforts to develop effective aquatic plant management programs. USDA scientists tested and evaluated many new herbicides to help resolve the aquatic weed problems.

An era of chemical weed control began during the period of 1945 to 1970. The new herbicide 2,4-D was extensively tested and used for the control of water hyacinth as well as various submersed and emersed species including Eurasian watermilfoil (Myriophyllum spicatum) in mid-Atlantic and northern states. Following the development of 2,4-D, the chemical industry made available an apparently inexhaustible supply of new weed control compounds for agriculture. What initially started as trial and error testing of terrestrial herbicides soon changed into a very intensive test program once a compound proved to be effective for a problem aquatic species.

Aquatic weed scientists reviewed the toxicity, environmental fate, and persistence of potential weed control compounds. The U.S. Fish and Wildlife Service established fish toxicity programs at several locations around the country. After initial herbicide screening studies, broad-based field trails were established to test the efficacy (the power to produce intended results, with herbicides usually the death of a plant) and selectivity of the herbicide. These tests were then followed by basic physiological studies that determined the most effective time during the growth of a plant and method of application to achieve the best results.

Aquatic plant managers rapidly accepted herbicides as an affordable means of solving increasing aquatic weed problems. New application techniques were developed and an intensive search was begun by industry for new aquatic herbicides. Whatever the end use of a body of water, there was usually a choice of available herbicide or algaecide that could adequately control aquatic weeds when used properly. Between 1945 and 1970, the chemical industry could justify spending development time and money on aquatic weed control research. Most herbicides would find a use determined by the parameters of cost, safety to non-target organisms, species specificity or resistance, and persistence in treated waters.

Although herbicides were tested to ensure that they were not acutely toxic to applicators and fish and wildlife, concerns soon arose over the long-term effects of herbicides on humans and aquatic ecosystems. In the early 1960's, public health authorities were concerned about pesticide persistence and in particular the effects of aquatic herbicides on potable water. The publication of Rachel Carson's (1962) Silent Spring gave momentum to environmental concerns over the long-term effects of pesticides in general. With the establishment of the United States Environmental Protection Agency (USEPA) in the early 1970s, aquatic scientists began to re-evaluate data packages prepared during testing of herbicides for aquatic use. Regardless of use limitations, research data generated in one area that dealt with a specific aquatic system, was subjected to additional testing and evaluation for use in other areas under different conditions. These limitations did not prevent early testing of many new herbicides, but they affected the survival or sales of many aquatic herbicides. The aquatic registrations of several aquatic herbicides were eventually withdrawn by industry because of the high cost of further testing. Effective aquatic herbicides that made it through the testing process quickly became national in scope but were few in number.

Many of the older herbicides were eventually phased out because of health and environmental concerns, but it is important to remember that these herbicides filled an important need between 1945 to 1970 and were generally used safely until they could be replaced by newer products. For example, certain toxic materials such as sodium arsenite continued to be used in the midwestern and northeastern United States throughout the 1950s and 1960s. Insight into why sodium arsenite remained available for such a long period of time was provided by Kenneth MacKenthum, a public health biologist. In Wisconsin, it was first used in 1926 for weed control and to enhance the recreational value of Madison area lakes. Qualified applicators, aware that sodium arsenite was a poison, made successful lake treatments with no harm to spray personnel, lake users, or to fish and fish food organisms. It was a broad spectrum herbicide controlling a wide range of submersed and emersed species; it also was relatively inexpensive. Sodium arsenite use ceased when new, biodegradable, selective and easier to use herbicides became available.

Of the many products tested for aquatic weed control between 1945 and 1970, the following were in operational control programs or in process of obtaining registration by 1970: sodium arsenite, copper sulfate, 2,4-D, silvex, diquat, endothall, dalapon, amitrole, simazine, dichlobenil, fenac, acrolein, aromatic solvents (usually grade B xylene), diuron and dicamba. By the mid-1980s, only three new compounds were being actively researched: glyphosate [N-(phosphonomethyl)glycine], fluridone [1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl](1H)-pyridone] and chelated copper formulations. What seemed to be an inexhaustible supply of potential new aquatic herbicides soon decreased to relatively few by 1989 due, in part, to political pressures from a growing environmental movement and increased regulatory demands for more and very expensive toxicological data. Industry support for aquatic herbicides waned because profits from a limited aquatic market became insufficient to support high costs of herbicide registration and additional testing required by federal and state agencies.

The discipline of aquatic weed science also began adjusting to social, political, and economic pressures after 1970 through more diversified research. There was a shift in aquatic plant management from an emphasis on operational problem solving to increased interest in basic knowledge, environmental concerns, alternative control methods, and concern for non-target organisms. This shift occurred in part because many of the major aquatic weed problems were under control or at least were not causing major economic losses. For example, successful introduction of the alligator-weed flea beetle (Agasicles hygrophyila) in the 1960s into the Southeast had significantly reduced aquatic weed problems caused by alligator-weed. The use of 2,4-D and the adoption of the philosophy of maintenance control (managing at the lowest plant level economically possible) soon resulted in the elimination of major water hyacinth problems on most southern waters.

Perhaps the most important factors involved in the shifting attitudes towards a concern with the total environment rather than the "immediacy of the weed problem" were the promises of cleaner water and new biological controls. For many aquatic scientists and much of the public-at-large, aquatic weed problems were viewed as the end result of excessive nutrient enrichment. In the 1970s, programs were instituted to reduce the nutrient enrichment (eutrophication) of the nation's waters. Between 1971 and 1989, major searches were also underway for effective biological solutions to aquatic weed problems. Attitudes towards aquatic weed problems and the techniques used to manage aquatic plants were strongly influenced by news stories on biological controls. For example, there was the "wonder fish", the grass carp (Ctenopharyngodon idella ). Three insects, two weevils (Neochetina bruchi and Neochetina eichhorniae) and a moth (Sameodes albiguttalis), were touted as the answer to the South's water hyacinth problem. These insects were followed in the news by insects for the control of water lettuce (Neohydronomus affinis and Neohydronomus pulchellus), Eurasian watermilfoil (Parapoynx stratiotata and Acentria ephemerella), and hydrilla (Bagous affinis and Hydrellia pakistanae). The media also ran stories on fungi, snails, manatees, and a host of other potential biocontrol organisms including water buffalo.

Despite high hopes for the ultimate success of nutrient control programs and biological controls, the reality of the 1980s was once again expanding aquatic weed problems. Non-native plants like hydrilla, Eurasian watermilfoil, and purple loosestrife (Lythrum salicaria) spread to many new areas and soon reached problematic levels. Eurasian watermilfoil became particularly problematic as it began to colonize northern lakes where people often had never experienced an aquatic weed problem and thought such weed problems were limited to southern waters or polluted waters. As more people built or purchased homes on lakes or used waters for recreation, the presence of native species of aquatic plants also became more problematic for some individuals, but other individuals began to argue that desirable native vegetation should not be controlled. Intense debates erupted over how much vegetation should be in a lake and how vegetation should be managed.

Aquatic plant management programs in the 1980s began to develop along a regional basis. Nutrient control programs and mechanical harvesting often became the methods of choice in the northern states where aquatic weeds have shorter growing seasons and a single annual harvest often provided control for the recreational season. Aquatic herbicides and biological control (i.e., grass carp, insects) methods were used more frequently in southern states. Although the technology for control was often available, factors beyond the direct control of aquatic plant managers regulated the availability of the methods of weed management. For example, many northern states legislatively prohibited the use of grass carp or through agency rules greatly restricted the use of aquatic herbicides.

Anyone plagued with aquatic plant problems usually demands use of any management activity that may relieve their problem. Drawdowns, rotovation, dyes, fertilization, benthic mats, suction dredging and other rather exotic means of weed control are generally considered as well as integrated weed control techniques. Aquatic plant managers, however, must consider budget, efficacy, public perception, water use priorities, legislative mandates, and other factors when choosing a course of action. Economics alone has not always been the determining factor, but the scale of aquatic weed problems can significantly influence courses of action.

Aquatic weed control activities in the public waters of Minnesota and Florida, two states with vastly different climates, were minimal prior to the 1960s because aquatic weed problems were relatively minor. Soon thereafter, public concern over the management of aquatic vegetation was heightened by an expansion of purple loosestrife and Eurasian watermilfoil in Minnesota and water hyacinth and hydrilla in Florida. Debates over what should be done and how it should be done became common in both states. Controversies between homeowners and fisheries biologists over the ecological value of vegetation fueled opposition to control programs. Eventually the two states evolved different game plans for the management of aquatic plants based on different social and political climates in the two states.

Grass carp for weed control were not permitted in Minnesota but were used experimentally in Florida and finally allowed in Florida after the development of triploid grass carp (a sterile grass carp with three sets of chromosomes, which prevent the fish from reproducing). Several herbicides are used in Minnesota and in Florida, however Florida allows treatments of larger portions of the littoral areas due to Florida lakes being shallower than Minnesota lakes. Both states use several means of mechanical harvesting to control problem aquatic plants. The amount of state money spent on aquatic plant control in the mid 1980's ranged from a half of a million dollars in Minnesota (which had only a few lakes infested with weeds) to over 13 million dollars in Florida.

The examples of aquatic plant management provided for Minnesota and Florida are meant to compare aquatic weed problems and management activities in two extreme latitudes. The weed problems are similar but of different magnitude and with different problem species: purple loosestrife versus water hyacinth and Eurasian watermilfoil versus hydrilla. The lakes and lake uses are also very different with dramatic seasonal changes occurring in northern lakes and minor changes in the South. Nevertheless, aquatic plant managers in these regions and throughout the United States share the same methods of control, the same controversial debates on how much and how to control aquatic weeds, and the continued advances of exotic species.