Frigid winter dealt 'deadly blow' to hemlock woolly adelgid in Pennsylvania but has not changed long-term impact, says DCNR; study of branch samples from 75 sites shows winter die-off, but entomologists warn of rapid infestation by remaining insects

Wendy Lisney

HARRISBURG, Pennsylvania , March 21, 2014 (press release) – The past winter of seemingly unending snowstorms and frigid temperatures has proved to be a strong ally for state woodland managers battling the No. 1 enemy of Pennsylvania hemlocks, but the reprieve could be short-lived, Department of Conservation and Natural Resources officials said today.

“The hemlock woolly adelgid has been dealt a deadly blow, ongoing forest research is showing us, but enough of the invasive insects remain to present a future threat to our invaluable state tree -- the Eastern hemlock,” said DCNR Secretary Ellen Ferretti. ”Cold weather has been helpful, in some cases killing all of the invasive insects in selected study areas, but it hasn’t changed the long-term impact this insect will have on hemlock.”

Since mid-January, the Bureau of Forestry collected hemlock branch samples from more than 75 sites statewide. Areas selected included Cook Forest and Clear Creek state parks where very large signature hemlocks enrich their forests.

“Four sites were surveyed in Cook Forest in early February and 308 adelgid were counted under the microscope – only one was determined to be alive,” Ferretti said. “Our forest researchers say this is fantastic news, but it by no means indicates the end of HWA as a problem in that park.

“For a park like Cook Forest, the mortality rate presents the managers with a very valuable asset -- time,” Ferretti said. “If this past winter had been similar to the winter of 2012-2013 the HWA population may have swept through the park faster than we could have kept up with it. This valuable time may allow the managers the opportunity to treat more hemlock stands before they start to show signs of decline that almost always follow an adelgid infestation.”

Statewide, DCNR research shows winter die-off of the insect was not as high as Cook Forest State Park, but the numbers still are very good.

“Caution is the watchword here as our entomologists point out remaining insects can foster infestation in a short time, even to areas where there was 100 percent die-off this winter,” Ferretti said. “To be sure, the widespread insect mortality presents time for the health of hemlocks to improve through new growth. Time for land managers along the leading edge of the infestation to get their plans developed and implemented to combat the infestation.”

Meanwhile, the DCNR secretary noted, winter die-off is not likely to have a pronounced effect on treatments planned jointly by the bureaus of state parks and forestry. Treatments are effective for more than three years, during which HWA populations could again rebound.

DCNR has embarked on a two-pronged effort that relies on selective application of insecticides and the release of predatory beetles. The cooperative effort among our bureaus of forestry, state parks and others in recent years has seen more than 100 sites and thousands of tree treated in counties across the state.

The woolly adelgid is a fluid-feeding insect, easily detected by telltale egg sacs resembling cotton swabs that cling to undersides of hemlock branches. Introduced into the United States from Asia, it first was discovered in southeastern Pennsylvania in 1969 and steadily has been spreading westward.

Homeowners and other private property owners can learn more about the woolly adelgid, damage it causes, and efforts to combat it at www.dcnr.state.pa.us (click on “Forestry,” then “Insects and Disease” at upper left).

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