Since the late 1880s, various chemicals, from sea-salt to copper to 2,4-D to fluridone, have been applied to our freshwaters to control the growth of invasive aquatic plants. Chemical development and use was spurred by the realization that human- and machine-power were not able to keep up with the explosive growth of certain invasive plant species, such as water hyacinth (Eichhornia crassipes) and hydrilla (Hydrilla verticillata).

However, contemporary plant managers rely on research and guidelines that have been developed throughout Florida's 100+ year history of using chemicals in the water to control invasive plants. Before reading about the herbicides themselves, you may want to know a bit more about Florida's history of using chemicals in the water to control invasive plants.

Although old photos and documents often show blocked rivers, washed out bridges, and other problems created by water hyacinth and other aquatic weeds, these mechanical/manual efforts did attain a degree of success, but were not able by themselves to keep waters clear of invasive aquatic plant problems.

The ineffectiveness and high cost of mechanical control and rapid regrowth of invasive plant populations prompted engineers to experiment with chemicals such as steam, sulfuric/hydrochloric acid, copper sulfate, sodium arsenate and other inorganic contact "desiccants". Of these, only copper sulfate continues to be used albeit extremely sparingly, today; the others being ineffective or toxic to non target plants, animals, and sometimes the people who applied them.

Herbicidal control 1950-1975
The discovery of the herbicidal properties of 2,4-D during the 1940s began an era of rapid development of new herbicides for a plethora of agricultural and other uses, including aquatic weed control. By 1947, water hyacinth was shown to be particularly susceptible to 2,4-D. This herbicide also was shown to be effective against the submersed Eurasian water milfoil (Myriophyllum spicatum) and other herbicides were discovered to be effective against canal weeds (Potamogeton, Chara, etc.) even in rapidly flowing water.

Herbicides were relatively less expensive and more efficient than previous mechanical or manual methods because they could be applied to large areas of weeds in a short time period and could be applied to shallow areas inaccessible to mechanical methods. The use of herbicides also provided longer periods of weed control because some plants often regrow quickly following mechanical removal.

By 1975, as many as 500 new pesticides were discovered annually by the chemical industry and total pesticide use was increasing dramatically internationally. The publication of "Poison on the Land" in England by J. Wentworth Day in 1957 followed by "Silent Spring" by Rachel Carson in 1962 clearly outlined environmental and human health concerns of widespread pesticide use and mis-use, and called for greater regulation of pesticide manufacturing, distribution, labeling, and use. Public concern for the environment in the United States was so widespread that the U.S. Environmental Protection Agency (EPA) was formed in 1970 and was given the responsibility for pesticide regulation, a responsibility formerly held by the U.S. Department of Agriculture.

This prompted a series of laws regulating chemical use to be passed by state and federal governments. By 1975 and continuing to the present, the passage of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA), and periodic amendments, greatly reduced new pesticide development and required extensive, expensive studies to "re-register" old pesticides to current standards. Pesticide registration procedures change over time as new technologies and testing methods are developed. All pesticides, including aquatic herbicides, were ordered to be "re-registered" by the U.S. EPA. Extensive studies on human exposure, carcinogenicity, effects on fish and wildlife, persistence, evaluation of metabolites and other breakdown products and many other tests are now required.

Testing for registration of aquatic herbicides is much more stringent than that for terrestrial herbicides. And regulations often require additional testing and registration for additional uses. For example, in addition to its registration for aquatic weed control, diquat has an FDA registration for treatment of fish parasites in fish hatcheries.

During this period, insufficient funding often resulted in weed problems becoming very serious and massive in size before action was taken. The lack of a funded, sustained and organized management plan often allowed the plants to grow for 2-3 years at a time. Aerial spraying of thousand-acre water hyacinth infestations was not uncommon in the southeastern United States, including Florida. This large scale spraying periodically lead to reduced oxygen in the water and subsequent fish kills.

Although aquatic herbicides enabled more economical and efficient weed management, large scale use and public concerns about potential environmental and human health problems prompted state and federal regulatory officials to begin to more closely monitor aquatic plant management programs, demand additional testing for safety, and to support additional research.

1975-Present
By the end of the 20th century, a worldwide increase in aquatic weed control resulted in the development of planned programs for aquatic weed management which include biological, mechanical, physical and chemical methodologies, ideally organized into an Integrated Pest Management (IPM) program.

Still, the number of herbicides registered for use, particularly in the United States, has decreased dramatically as studies required for EPA re-registration increased along with expenses associated with these studies. In 2004, only eight general herbicide compounds are approved for use in Florida waters by the US EPA.

Part of the preceeding was excerpted from, Role of Herbicides in Aquatic Plant Management Programs, by W.T. Haller and A.M. Fox, 2002.

EVEN A BIT MORE...
Here is another History of Aquatic Plant Management by J.C. Joyce and K.A. Langeland.

YES, EVEN A BIT MORE...
Here is another History of Aquatic Weed Control in the U.S. by D. Canfield and M. Hoyer.