Mosquito control season begins with spraying wooded wetlands

Weather permitting, the Department of Natural Resources and Environmental Conrtol’s Mosquito Control Section has started its annual spring woodland-pool spraying this week, treating wooded wetlands for control of immature (larval) mosquitoes near populated areas in New Castle, Kent and Sussex counties. Approximately 5,000 to 8,000 acres with woodland pools where early season mosquitoes breed in quantity will be strategically larvicided by helicopter and possibly fixed-wing aircraft.

If larval stages of these early season mosquitoes are not successfully controlled, an intolerable number of biting adult mosquitoes could take wing by early to mid-May and remain through late June, becoming particularly troublesome within one to two miles of their woodland pool origins, significantly affecting local quality of life for residents and visitors alike, said Mosquito Control Administrator Dr. William Meredith. As in past years, only woodland pools near populated areas will be treated.

“Delaware has about 100,000 acres of wet woodlands in the spring, and it’s not possible logistically or for budgetary reasons to larvicide all woodland mosquito-rearing habitats. Additionally, not all of these wet woodlands contain pool habitats suitable for producing large numbers of mosquitoes,” said Meredith. “Targeting woodland pools that are good habitats for mosquito larvae near populated areas is the best return on investment in providing mosquito relief to the most people.”

Over the next few weeks, mosquito control will apply a bacterially produced insecticide, Bti, for larval mosquito control. “Like all insecticides used by the Mosquito Control Section, the U.S. Environmental Protection Agency has determined that Bti, when used in accordance with all EPA-approved instructions as required by federal law, can be applied without posing unreasonable risk to human health, wildlife or the environment,” said Meredith.

The amount of spraying needed is determined by where and how wet the woodlands are, which can vary from year to year depending on the location and amount of precipitation that has occurred over the past autumn, winter and early spring. At present, with the exception of some wetter areas in Sussex County, woodland pool acreage is below normal statewide, and larval densities also appear a bit lower than normal.

Relatively cool weather this spring is also slowing larval growth progression.

These factors can be favorable for effectively treating in timely manner woodland pool mosquito production during early spring. However, all of this can quickly change, depending upon rainfall amounts and temperatures over the next few weeks.

Aerial spraying of woodland pools must be completed before the forest canopy fills in with foliage, usually around mid-April, because leaves prevent the insecticide from reaching pools and other wet spots containing larvae on the forest floor. The spring campaign marks the beginning of Delaware’s mosquito season, which in most years continues until sometime between mid-October and early November, depending upon when the first killing frost occurs.

Throughout the rest of the year, mosquito control needs expand to include saltmarsh mosquito control, treatment of myriad types of freshwater habitats to control other species of freshwater mosquitoes, and control of mosquitoes in urban or developed areas that are produced in standing water or container habitats.

As in the past, advance public notice of when and where spraying will occur this year will be given daily via radio announcements, by calling 800-338-8181 toll-free, or by going to at www.dnrec.delaware.gov/fw/Services/Pages/MosquitoSection.aspx and clicking “Mosquito Spraying Announcements.” Interested parties may also subscribe to receive email notices by visiting DNREC’s homepage, clicking on “Email List Subscription” under Services and following directions to sign up for mosquito control spray announcements.

During mosquito season, the public is encouraged to do its part to reduce mosquito-rearing habitat by cleaning clogged rain gutters, keeping fresh water in birdbaths, draining abandoned swimming pools and emptying standing water from such containers as scrap tires, cans, flower pot liners, unused water cisterns, upright wheelbarrows, uncovered trash cans, depressions in tarps covering boats or other objects stored outside.

To request local relief, call mosquito control’s field offices: Milford office, 302-422-1512, serving the southern half of Kent County south of Dover and all of Sussex County.

For more information about Delaware’s Mosquito Control program, call the Dover office at 302-739-9917.