Tree defoliation by gypsy moath sets Md. record

September 30, 1990|By Luther Young

It was a year of records for the gypsy moth caterpillar in Maryland, as the leaf-eating pest continued its decadelong advance through the state into Southern Maryland and the Eastern Shore.

The caterpillars defoliated 133,062 acres of trees -- a new high -- despite a $2.5 million aerial spraying program that treated a record 187,723 acres in 21 counties and Baltimore City.

"It's not the best year we've ever had against the gypsy moth," said Robert H. Tichenor, chief of forest pest management for the state Agriculture Department. "What's encouraging is that spraying was extremely effective in the central part of the state."

Officials are cautiously optimistic that pest populations have peaked in Baltimore and in Carroll, Frederick, Harford, Howard, Montgomery, Prince George's and Baltimore counties, which accounted for 40 percent of statewide defoliation last year and more than 50 percent in 1988.

This year, those areas suffered only 13 percent of the total defoliation, less than 18,000 acres, through a combination of extensive spraying and a natural drop in gypsy moth numbers FTC typical of population cycles exhibited during its 120-year spread down the East Coast.

But the aerial insecticide treatments didn't prevent severe defoliation in Western Maryland, in part because of adverse weather conditions during spraying this spring.

Garrett County had 36,705 acres of damage, compared with last year's 13,877, although nearly 97,000 acres were sprayed.

"Just two counties, Garrett and Allegany, had more defoliation than the entire state in '86 or '88," Mr. Tichenor said.

Allegany, with more than 12,000 acres sprayed, reported 24,179 acres damaged, four times more than last year.

The damage in Western Maryland in combination with the Upper Eastern Shore -- defoliation was particularly severe in Queen Anne's, Kent and Caroline counties -- pushed the state's total over 100,000 acres for the first time.

"The gypsy moth is knocking on the door in Charles, St. Mary's and Calvert counties, and there's no reason to think it won't keep building up on the Shore next year," Mr. Tichenor said.

The first Maryland defoliation occurred in Cecil County in 1981, he said.

A European import released accidentally in Medford, Mass., in 1869, the moth -- which feasts on the leaves of hardwood trees such as oaks during its caterpillar stage -- has relentlessly marched south and west, defoliating a record 12.9 million acres in 12 states in 1981.

Fifteen states and the District of Columbia reported an estimated 7.5 million acres of defoliation this year, the highest since 8.1 million acres in 1982, according to entomologist Daniel Twardus, with the U.S. Forest Service in Morgantown, W.Va.

The pest surged again in New England after years of relative quiet following the 1982 spurt, and it advanced further into Michigan, Ohio, Virginia, West Virginia and North Carolina, Mr. Twardus said.

Virginia reported 594,000 acres damaged, and West Virginia 338,000 acres this year.

But the major victim this year was Pennsylvania, whose extensive hardwood forests suffered defoliation unprecedented in the U.S. history of the gypsy moth: 4.4 million acres, an increase of nearly 300 percent over 1989.

And that devastation occurred despite an aerial spraying program that treated nearly 400,000 acres at a cost of between $4 million and $5 million.

"There's really no way to control the gypsy moth. All we can do is try to preserve the most valuable trees and forest," said Mr. Tichenor, who noted that this year's record spraying in Maryland treated less than 10 percent of the state's susceptible forested land.

Costs for the "cooperative suppression program" are split three ways, with the Forest Service paying half and the state and participating counties each paying one-quarter. Maryland also sprayed 5,600 acres of federal land at U.S. expense, and the federal agencies themselves arranged for treatment of another 28,700 acres at government facilities.

Four counties -- Garrett, Anne Arundel, Caroline and Montgomery -- contracted with private spraying companies for additional coverage, for a total of 80,664 acres.

Some communities did the same, for a variety of reasons: They were not included in the state program, they wanted more protection than the state offered or they wanted the biological pesticide Bt sprayed instead of diflubenzuron, or Dimilin.

Two years ago, a controversy erupted in the Baltimore metropolitan area over human health and environmental concerns about Dimilin, a chemical insecticide that can harm crustaceans.

The Agriculture Department reserves Bt for spraying near water and considers Dimilin safe and preferable for all other areas.

Of the trees sprayed by the state this year, 108,983 acres were treated with Bt and 84,404 acres with Dimilin.

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