Md. steps up killing of gypsy moths

$4 million allocated to double aerial spraying of trees

May 10, 2008|By Tom Pelton | Tom Pelton,Sun reporter

Maryland is doubling its effort to kill gypsy moths, an invasive Eurasian pest that defoliated tens of thousands of acres of trees across the state last year.

Airplanes are spraying pesticides on about 100,000 acres of trees in Baltimore County, Western Maryland and elsewhere. It's a $4 million project that state officials hope will beat back an egg-laying spree last year by the leaf-munching menaces.

"There are a lot of gypsy moths out there, and we are trying to suppress them so people don't have to deal with them in their parks or homes," said Steve Tilley, an entomologist at the Maryland Department of Agriculture.

By contrast, last year the state sprayed 50,000 acres. Contractors target residential areas with lots of trees that were stripped by the moths last year, spraying commonly used pesticides called Bacillus thuringiensis and Dimilin.

A drought last spring created an explosion in moth larvae, which are hairy brown caterpillars. The larvae devoured the leaves of 68,460 acres of trees last year - the most in more than a decade.

One of those whose property was swarming with the caterpillars last year was Mike Richardson, 40, a bartender from Baltimore County. His Freeland home had fuzzy invaders crawling all over it. They hit the oaks, white pines and sugar maples in his yard.

"I totally agree with the spraying because they do so much damage," he said. "If the larvae were to defoliate the area again this year, a lot of trees would die."

Gypsy moths, native to Asia and Europe, were brought to the U.S. in 1868 by a Massachusetts scientist who was trying to cross-breed them with silk worms.

The larvae escaped from Leopold Trouvelot's lab and started eating his trees. Because their hairy bodies are unappetizing to local birds, they have no natural predators. By the 1970s, gypsy moths were denuding trees from upstate New York to Maryland.

For more than three decades, Maryland has been spraying pesticides on the larvae as they emerge just when leaves first unfold on trees.

The high point of spraying came in 1990, when the state treated 187,000 acres. But over the past decade, federal and state funding for the fight against gypsy moths was slashed - until the state's boost this year.

Weather plays an important role in moth multiplication. Lots of rain encourages the growth of a fungus called Entomophaga maimaiga that kills the moth larvae. Last spring was dry, so little fungus grew - giving a green light to the moths.

This spring has been wetter, and that could also help with limiting the larvae.

Garrett County administrator Monty Pagenhardt, whose section of Western Maryland was ravaged by the moths last year, said he hopes this year's rain and the added pesticides will provide a one-two punch.

"It was very bad last year, and this year was projected to be even worse," said Pagenhardt, whose county is chipping in $49,000 for spraying this year. "Right now we're having a wet spring, and that fungus thrives on damp moldy springs, and that will help, too."

Aerial surveys in the spring help officials judge which sections of the state should be targeted for spraying. Property owners whose homes will be sprayed receive warning letters recommending that people stay inside during the application.

The spraying started April 30 in Anne Arundel, Talbot and Worcester counties; continued this week in Baltimore County; and over the next month will move west across the state, from Carroll to Garrett counties, finishing in early June, according to state officials.

For a listing of the exact locations and dates of spraying, go to the Maryland Department of Agriculture's Web site at

One of the compounds being used is Bacillus thuringiensis (known as Bt), a pesticide made from a naturally occurring soil bacteria that is toxic to insects.

Another is Dimilin, an insect growth regulator that can also be poisonous to aquatic invertebrates living in streams.

"Harmful if absorbed through skin or inhaled. Avoid contact with eyes, skin or clothing," warns the label on Dimilin. "Avoid breathing spray mist."

Tilley, the entomologist at the state Agriculture Department, said he has been spraying the chemicals for more than two decades and hasn't heard any complaints about human health problems.

But he added that people should stay inside, just to be careful. "People see the airplanes or helicopters flying by and they go out and look at it - and that's not a good idea," said Tilley. "The pesticides we are using are safe, but the best idea is to reduce your exposure."

Ruth Berlin, executive director of the Maryland Pesticide Network, a health advocacy organization, disagreed that the chemicals are safe.

"The truth is that no pesticide is safe," she said. "There is a growing body of research that pesticides affect the public health and the watershed, and people are becoming increasingly concerned."

The U.S. Environmental Protection Agency, however, says that Bt "presents little risk" to mammals. Dimilin "has been shown to be slightly toxic," but the danger is low enough that most spraying presents an "insignificant" risk to people, EPA says.

Baltimore County Councilman T. Bryan McIntire said it would be "disastrous" if the state stopped spraying: "I am very grateful that they are doing more spraying this year. But it's still not enough, because there are areas that still have a strong presence of the gypsy moths."

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