March 2002 Source Reduction Source reduction, also known as physical or permanent control, is the actual elimination of habitat conducive to the production of mosquitoes. Source reduction is, initially, quite costly but because it solves the mosquito problem, it is actually the most cost effective method of mosquito control and virtually eliminates the need for pesticide usage in nearby areas. Source reduction can be as simple as properly discarding old tires and other water holding items or as complex as Rotational Impoundment Management (RIM) of vast coastal salt marsh and mangrove swamps.
The history of source reduction efforts in Florida dates back to the 1920's when ditching of high marshes along coastal areas was done by hand or with explosives. Other projects included the filling of wetlands and the creation of impoundments. While all these activities had mosquito control benefits, environmental impacts occurring from their implementation have been realized. Since the 1980's a concerted effort has been made to restore impacted habitats. Today source reduction activities have been modified to minimize environmental impacts yet still work effectively to control mosquitoes. Rotational Impounding Management (RIM), Open Marsh Water Management (OMWM), constructing and maintaining drainage ditch systems, the design and engineering of stormwater systems, the control of certain aquatic plant species, proper treatment of domestic, agricultural, and industrial wastewater, waste tire disposal facilities, and the education of the public are all techniques that can be used to reduce or eliminate mosquito habitat.
RIM, Rotational Impoundment Management, is an extensive system of dikes, culverts and pumps used to keep coastal marsh areas flooded and still maintain an exchange of water. By keeping these areas flooded it eliminates the habitat saltmarsh mosquitoes use to lay their eggs (damp marsh soil). The pumps exchange the water to keep it fresh and the culverts allow nutrients, fish and other organisms to move in and out of the marsh. RIM is currently considered the most favorable technique because it accomplishes mosquito control while allowing the marsh to function, close to natural, most of the year.
OMWM, Open Marsh Water Management, is a network of shallow ditches dug to connect permanent water habitats in the open salt marsh. These ditches allow larvae eating fish the ability to access mosquito breeding habitat. OMWM has been done in South Walton and can be seen on aerial maps of the area.
Drainage ditch systems, like those dug in South Walton, mostly north of Highway 98, function both as a flood control system and as a source reduction technique for mosquito control. They provide flood control by conveying stormwater quickly to the Bay and they eliminate mosquito habitat by lowering the water table and allowing water to percolate quicker. Without this ditch system most of South Walton would be like a saturated sponge, producing large numbers of mosquitoes every time it rained. In South Walton we maintain 45 drainage ditches, about 10 ½ miles worth.
Stormwater systems are designed with mosquito control in mind. Drainage retention areas (DRA) for stormwater runoff are designed as wet or dry. The dry DRA is designed for soil types that percolate rapidly, within 3 days. The wet DRA is designed for areas that have a high water table and/or soils that don’t percolate well. Wet DRA’s are fine, even favorable because the habitat stabilizes as an aquatic system in which mosquito fish and other natural predators can become established and control mosquitoes.
Wastewater treatment systems can be onsite septic tanks utilizing anaerobic bacteria to breakdown the nutrient load or sewage treatment facilities that use aerobic bacteria to digest the nutrient load of the wastewater. Septic tanks and their associated drainfields, when properly sized and in the proper soil, are safe and efficient systems. Mosquito problems occur if there is access to the septic tank by adult mosquitoes or if drainfields become saturated and the wastewater comes to the surface or migrates laterally into nearby swales or ditches. Sewer systems transfer sewage to a central wastewater treatment facility, thereby eliminating thousands of individual septic tank systems. Treatment of agricultural or industrial wastewater is usually done on-site, decreasing nutrient loads using techniques similar to those of large regional sewage treatment plants. These small on-site treatment systems are called “package plants.” Mosquito problems occur in sewage treatment plants when the design capacity of the facility is exceeded. Whether by spray irrigation, rapid dry ponds or use of aquatic plant systems, exceeding their ability to handle the nutrient load of the wastewater being supplied, will invite mosquito problems.
Elimination of certain aquatic plants from a habitat is also a technique of source reduction. Removal, physically or with herbicides, alters mosquito habitat just enough to discourage mosquito breeding. Elimination of emergent vegetation removes shade, reduces stagnation, and takes away the hiding areas that protect larva from fish and other natural predators. In addition to habitat alteration, several species of mosquitoes utilize specific plants to obtain their oxygen needs while in the larval stage. By eliminating the plant you also eliminate the mosquito specie associated with that plant.
Waste tire disposal facilities are another form of source reduction. Old tires out in the weather are a perfect mosquito breeding place. They catch water and it doesn’t get out, they provide shade so the water doesn’t get too hot, they usually don’t support natural predators and they are pretty much indestructible. Other water holding items, as well as tires, can support mosquito production. In South Walton citizens can bring waste tires and old appliances to our facility and we will dispose of them, free of charge. Another activity we perform is residential inspections. When we suspect a container mosquito problem we will inspect the property at and around the citizen’s complaint. If we find containers breeding mosquitoes we inform the property owner of our findings. A lot of people think that by “just spraying” it will get rid of their problem, it doesn’t. Mosquitoes continue to emerge from the containers and the problem never ends until the containers, the sources, are eliminated.
This brings us to our final method of source reduction, education. Whether it is one on one education of the homeowner; showing them the larva in a bird bath, raingutter, animal watering buckets, old tires, tree holes, tarps covering equipment, and other water holding items or by giving presentations to civic groups or at schools, understanding and identifying what causes mosquito problems is the first and most important step to solving the problem. In South Walton we will be happy to provide an educational presentation to schools, civic or homeowner associations, just call us at 850 267-2112. |