Presented by: Marty Scholl, Ecological Management Supervisor; Sacramento-Yolo Mosquito & Vector Control District, CA
California’s Sac-Yolo Mosquito and Vector Control district spans the bottom end of the Sacramento Valley and the top end of the San Joaquin valley. The district is home to a series of rivers that converge to make up what’s called the California Delta, which contains numerous public and private managed wetlands. A movement to restore wetlands is being experienced not only in California, but across the country. If left unchecked, however, wetlands can become prime breeding grounds for floodwater mosquitoes that pose a risk to public health.
The complex Delta landscape provides numerous challenges for the Sac-Yolo district, challenges which require thoughtful and creative management. A key presenter at Valent BioSciences’ January 19, Virtual Floodwater Mosquito Control Summit for the Western US, Sac-Yolo’s Ecological Management Supervisor Marty Scholl shared the district’s Managed Wetlands approach with an audience totaling 275 mosquito abatement professionals and other stakeholders.
In the Sac-Yolo district, wetlands ownership runs the gamut of federal, state, and county agencies as well as non-agency entities such as conservancies, wildlife organizations, and private estates and hunting grounds. Some of the wetlands are natural, but a significant portion of the acreage is manually flooded at various points throughout the year. (insert image from slide 11 in this general vicinity)
The close proximity of these locations to urban areas in and around Sacramento, and the corresponding risk of vector-borne disease to public health, makes mosquito control in wetlands a priority. Federal agency owners such as the US Fish and Wildlife Service and the Bureau of Land Management, along with State agencies such as the California Department of Fish and Wildlife, the Department of Water Resources, and the Department of Parks and Recreation may oversee management of some or all of their own wetlands. For many non-agency wetlands, however, the Sac-Yolo district is called upon to help owners to actively manage mosquito populations. Scholl indicated this is where his team spends much of its time.
While the district treats a small amount of permanent wetlands, more of its resources are required for wetlands that are dry for most of the year, then flooded. Scholl said these wetlands range from private hunting grounds to agricultural land (mostly rice), totaling more than 60,000 acres. He said that a typical scenario is wetlands that hold their water through the winter months, then drain it sometime between March and May to promote vegetation growth. Irrigation is then used for 30 to 90 days to drown weeds and germinate desirable plants, then perimeters are mown down and the ground is disked under toward the end of summer. At some point in the late summer or fall, the lands are then flash flooded to moisten the soil, and the cycle repeats.
Communication and Collaboration
Scholl made it clear that effective control in their managed wetlands starts with proactive communication and collaboration with property owners. To assist in these efforts, the district created a Mosquito Reduction Best Management Practices Manual (BMP)s, available on its website. First published in 2008, the BMP Manual was compiled from several sources including scientific literature, collaborative inter–agency documents, and experienced vector control professionals. The Manual lays out the guidelines for program development and execution in managed wetlands and other source areas.
Plan development starts from scratch for a new wetland area or involves an annual review process for existing programs. Regardless, Scholl’s first step is to understand what the property manager is trying to accomplish so they can determine how the district can help and where it fits in. Potential treatment areas can range from very small to more than ten thousand acres.
Together with ownership, Scholl facilitates a pre-season meeting to review how the Sac-Yolo district approaches different types of mosquitoes and the different habitats that can be found on the property. Since it promotes an Integrated Vector Management strategy, the district helps property owners understand mosquito control technology and the possibilities and limitations of each. Beyond the discussion of annual goals, the pre-season meeting includes important topics such as irrigation timing, fall flooding timing, and timing of maintenance. Central to all of these discussions, of course, are costs, and how BMPs can be utilized to keep costs down both for the district and property owner. In addition to application services, the district offers imaging services, mowing and backhoe services, and heavy equipment rentals.
Since the district is responsible for managing such a wide area that includes both urban and rural areas, demands on district resources during the summer months are high. As a result, Sac-Yolo has implemented an innovative cost share incentive program to encourage managed wetland property owners to delay flooding as late into the fall as possible. By agreeing to delay application of floodwater larvicides into the latter part of the year, property owners can reduce their portion of material costs by as much as 100%. (See Fall Flooding Cost Share)
Sac-Yolo uses technology to its advantage. Unmanned aerial system imaging helps the team understand the dynamics of the changing landscape and what application technologies will make the most sense, and when. In addition to fixed wing aircraft, the team also makes extensive use of drones in areas where it doesn’t make sense to treat with a plane.
From a product standpoint, Scholl says he tries to use single brood Bacillus thuringiensis israelensis (Bti) when possible, especially in habitats with open water and less vegetation. In the fall, he looks at using residual products, initially, depending on flood timing. If the property will be flooded in early September, he starts with a residual followed by a cleanup, and often uses two to three Bti or single brood products to help manage resistance.
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