After a "rain delay" Tuesday, pesticide spraying is set to begin in the first of two Baltimore County neighborhoods where health officials say they've identified two new cases of West Nile virus.
The Maryland Department of Agriculture is to spray parts of Catonsville after 7:30 p.m. Wednesday (Sept. 19) and again on the evening of Sept. 26. A planned spraying Tuesday night in Pikesville was postponed because of stormy weather; spraying there is now scheduled to take place Sept. 24 and Oct. 1, also after 7:30 p.m.
State agricultural officials also announced Wednesday new spraying in Anne Arundel County. Eastport Terrace, Knightsbridge, Primrose Acres, and Truxton Heights will be sprayed on Sept. 24 and Oct. 1 after 7:30 p.m., weather permitting.
State agriculture officials urge residents to stay indoors during the truck-borne spraying, to minimize direct contact with the pesticide, Biomist 30-30. It may also be advisable to keep cats and dogs inside, based on a fact sheet by the National Pesticide Information Center.
Biomist's active ingredient is permethrin, a synthetic pyrethroid that is approved by the Environmental Protection Agency for use in mosquito control and in controlling pests on some farm crops.
Permethrin is deemed of "low toxicity" to people and mammals in general, but the pesticide information center reports there've been reports of cats and dogs showing signs their skin is burning or itching, as demonstrated by "paw flickingor ear, tail or skin twitching, or rolling on the ground."
While those effects are considered mild and temporary, permethrin is extremely toxic to bees, fish and other aquatic organisms, according to the pesticide information center. At least some of the streets to be sprayed border streams.
Michael Cantwell, the agriculture department's mosquito control manager, said the pesticide is being sprayed at night, when bees are not active. The Biomist also will be diluted, he said, to minimize chances of harming fish and aquatic insects.
The amount of permethrin being applied will average .0035 pounds per acre, which is considered an "ultra-low volume dose," Cantwell said.
Even at that low a dose, Cantwell said one spraying should produce a "good knockdown" of mosquitoes, which are generally more active at night. To really reduce an area's mosquito population, he noted, repeated sprayings would be called for. But the onset of cool fall weather could obviate the need for many more sprayings, he suggested.
The Maryland Pesticide Network, which tends to view chemical insect controls skeptically, acknowledges the concern about West Nile virus, which so far has logged 25 cases in the state and been blamed in two deaths. But the group contends that spraying is the least effective long-term method for controlling mosquitoes. Removing breeding areas and going after mosquitoe larvae are better approaches, they argue, without exposing people, pets and fish and other insects to potential risks.
Cantwell acknowledges that health authorities consider spraying adult mosquitoes a last resort of sorts. But he said it's hard to target mosquito breeding areas because they're seemingly everywhere. He pointed out that a survey about a decade ago, when West Nile first appeared in Maryland, found containers with standing water where mosquitoes could breed in one out of every three households checked.