1. How did the Corps get involved in Invasive Species Management?
The Corps became involved in invasive species management in the late 1800’s with the introduction of the water hyacinth. Water hyacinths were introduced into the United States in the 1880's and by 1890 their populations had grown to such an extent as to impede private and commercial river traffic in both Florida and Louisiana. The states of Florida and Louisiana requested assistance from Congress to solve the problem. Congressional interest resulted in the passage of the Rivers and Harbors Act of 1899, and tasked the Corps with solving the invasive aquatic plant problem in affected Federal navigable waterways. Through various other congressional actions, executive orders and with the introduction of new invasive species, the Corps has been involved in invasive species management ever since.
Executive Order 13112, signed February 3, 1999, directs Federal agencies to “(i) prevent the introduction of invasive species, (ii) detect and respond rapidly to and control populations of such species in a cost-effective and environmentally sound manner; (iii) monitor invasive species populations accurately and reliably; (iv) provide for restoration of native species and habitat conditions in ecosystems that have been invaded; (v) conduct research on invasive species and develop technologies to prevent introduction and provide or environmentally sound control of invasive species; and (vi) promote public education on invasive species and the means to address them”. The Federal agencies are also directed not to “authorize, fund, or carry out actions that it believes are likely to cause or promote the introduction or spread of invasive species in the United States or elsewhere unless pursuant to guidelines that it has prescribed, the agency has determined and made public its determination that the benefits of such actions clearly outweigh the potential harm caused by invasive species; and that all feasible and prudent measures to minimize risk of harm will be taken in conjunction with the actions.”
The Jacksonville District has many years of experience with aquatic plant management and is home to the Aquatic Plant Control Operations Support Center (APCOSC). The APCOSC was established by Headquarters, U.S. Army Corps of Engineers (HQ) to serve as the Corps-wide center of expertise in the operational aspects of aquatic plant management. HQ also established the Aquatic Plant Control Research Program at the Engineer Research and Development Center (ERDC) in Vicksburg, Mississippi. ERDC is the largest Civil Engineering and Environmental Quality Research and Development complex in the United States. The Aquatic Plant Control Research Program is administered by the office of the Technical Director for Civil Works Environmental Sciences and Engineering at the ERDC Environmental Laboratory. It provides Federal money to fund research into the various aspects of aquatic plant control, including: chemical control, biological control, and mechanical control.
2. What invasive plants does the Corps control and why?
Under the Removal of Aquatic Growth (RAG) program, the Corps predominantly controls water hyacinth (Eichhornia crassipes), water lettuce (Pistia stratiotes) and tussocks (assorted species). However, the Corps has the authority to control any species that poses a threat to navigation, including native vegetation.
The water hyacinth was originally introduced from South America in the late 1800’s. The growth rate of water hyacinth is among the highest known of any plant. The plant’s ability to double in biomass in 7 to 12 days means that 10 of these plants can grow to cover 1 acre in a single growing season. Under optimum growing conditions, one acre of water hyacinth can deposit about 1.7 tons of organic material (dry weight of leaves, stems and roots) on the bottom of a water body per year. If not controlled, these plants will take over a water body and adversely impact navigation, flood control, recreation, native vegetation, wildlife, and fishes.
Water lettuce has been observed in Florida as early as 1765. It is believed that water lettuce may have originally been transported here in the ballast water of early explorers’ ships. Like water hyacinth, water lettuce has a very high growth rate. Large mats of water lettuce can rapidly cover a water body, blocking sunlight and the exchange of gases at the air-water interface. This can lead to the death of other submerged plant species, decreased oxygen levels and poor conditions for fish and other wildlife. In addition to the ecological effects, water lettuce also adversely impacts navigation, flood control and recreation.
The Corps also treats species such as melaleuca, (Melaleuca quinquenervia), Brazilian pepper (Schinus terebinthifolius), hydrilla (Hydrilla verticillata) and others which are on the Florida Exotic Plant Pest Council (FLEPPC) Category I and Category II invasive species lists. Category I species are defined as invasive plants that have impacted native plant communities by outcompeting native species, altering community structure or function or hybridizing with native species. Those on the Category II list have not yet had this type of impact, but their numbers are increasing and they may be approaching Category I status. The Corps treats a number of these species as part of their Comprehensive Everglades Restoration Plan (CERP) projects, Environmental Stewardship, Operations & Maintenance projects and in cooperation with other state and federal agencies.
The Corps has recently identified two new species that pose a threat on Lake Okeechobee,South American water grass (Luziola subintegra) and crested floating heart (Nymphoides cristata). Both of these species were recently added to the FLEPPC Category I list.
3. How does the Corps control these invasive plants?
The Corps utilizes Integrated Pest Management (IPM) strategies which include a combination of biological, mechanical, and chemical control measures.
Biological control has involved the release of insects that feed on the target plants. The release of a bio-control agent into the U.S. requires years of research to determine that the agent will not cause adverse impacts to plant or animal life in this country. The Corps funded portions of the research by ERDC, U.S. Department of Agriculture, and various U.S. and foreign Universities to allow these biocontrol agents to be brought into the U.S. Insects have been released to control alligatorweed, water hyacinth, water lettuce, old world climbing fern, hydrilla and melaleuca. So far, only the insects to control alligatorweed have been completely successful (eliminating the need to use herbicide to treat the plants). Research continues to identify more effective biological control agents.
Mechanical control involves the use of various types of machinery to chop, harvest and remove plants and tussock material. Mechanical control is extremely expensive, cannot be utilized in all areas, can cause damage to native vegetation, and kills some fish and wildlife that cannot escape during operations. When harvesters replaced chemical control on Lake Okeechobee in the mid 1980's, the plants outgrew the ability of the harvesters to remove them. Chemical control had to be utilized to gain control of the plant populations. The effort to regain control of the floating vegetation took much more herbicide than normal operations. The Corps and the State of Florida continue to evaluate new mechanical harvesters. Mechanical control is used for tussock removal, cutting trails, removing plants around water intake structures and opening navigation channels, water control structures and navigational locks. This control method is not cost effective or practical for large-scale control of water hyacinth and water lettuce.
Chemical control involves the application of aquatic herbicides on target plants. The chemicals used are labeled for use in the aquatic environment by the U.S. Environmental Protection Agency (EPA) and approved by the State of Florida. When used as directed, these chemicals are safe for people and the environment. Federal and State law requires the herbicide applicators be properly trained. The Florida Department of Agriculture and Consumer Services (FDACS) certifies applicators and the University of Florida Institute of Food and Agricultural Sciences (IFAS) provides training and testing services for the certification of applicators.
4. What herbicides are used in the Corps' Aquatic Plant Control Program?
The Corps uses herbicides labeled for the environment that work is being conducted in and that are approved by the EPA. The EPA develops labels for each herbicide which identify how they are to be used. Using a herbicide in a manner that is inconsistent with its label is against the law. For more information about the use of herbicide to control invasive aquatic plants, please visit the University of Florida control methods website. For more detailed information about the herbicides approved for aquatic use in Florida, please visit the University of Florida herbicide reference guide website.
5. What is the Corps' philosophy for invasive species management?
The Corps utilizes Integrated Pest Management (IPM) techniques to achieve maintenance control of problematic invasive species. IPM techniques include biological, chemical and mechanical control (as described in Question 3). Maintenance control is defined as controlling an invasive species so that its population can be maintained at the lowest feasible level. For the most widespread invasive species, such as water hyacinth, water lettuce, melaleuca, and Brazilian pepper, complete eradication is not a realistic goal. Maintenance control allows the populations to be kept in check while minimizing the amount of herbicide used, decreasing the deposition of organic matter and reducing the management costs. Maintenance control also prevents species from spreading further and having greater impacts on the environment.
For newly emerging invasive species problems, the Corps embraces the philosophy of Early Detection, Rapid Response (EDRR). If monitoring efforts detect a new invasive species in an area, there should be a rapid response to the threat. Ideally, this will lead to eradication of the newly identified invasive species and eliminate the need for future control efforts, the cost of which would increase exponentially with time if the species was not treated.