DCNR Begins Aerial Treatment to Mitigate Spongy Moth Impact on Forest Ecosystems, Reports Significant Improvement in Defoliation Caused by Pests
HARRISBURG – Monday, the Department of Conservation and Natural Resources (DCNR) announced that the beginning of aerial spraying of state woodlands to combat spongy moth (Lymantria dispar dispar, formerly known as the gypsy moth) populations poised for spring outbreaks in many sections of Pennsylvania.
In 2024, spongy moth defoliated 595,324 forest acres in Pennsylvania. This year’s treatment program covers just under 75,000 forest acres—a significant decrease from over 227,000 forest acres last year and 290,000 the year before.
“Pennsylvania’s forests are one of the Commonwealth’s most valuable natural assets, providing clean air and water, recreation opportunities, and a sustainable timber resource,” State Forester Seth Cassell said. “Each year, spongy moths pose a significant threat to our native oak forests, and DCNR works to target and suppress outbreaks to prevent widespread tree loss. This reduction is a strong indication that our suppression efforts are making a difference, and we remain committed to protecting these vital forested landscapes.”
Feeding while in the larval or caterpillar stage, the insect usually hatches and begins feeding from mid- to late April in southern Pennsylvania, and in early to mid-May in the northern part of the state. Oak, apple, sweet gum, basswood, birch, aspen, and willow trees are most affected by the spongy moth. DCNR’s Bureau of Forestry experts note the state’s oak tree stands are especially vulnerable to infestations.
DCNR will oversee spraying of 65 sites totaling 74,779 acres. Included will be portions of 5 state forests and 7 state parks, in 13 counties located in southcentral, central, northcentral, and northeast Pennsylvania.
In addition to DCNR’s spray program, the Pennsylvania Game Commission will also be conducting an aerial spray program in 2025 on approximately 38,000 acres of State Game Lands.
State Forests and Parks to be sprayed include:
- Boyd Big Preserve Tree Conservation Area, Dauphin County
- Delaware State Forest, Pike and Monroe County
- Ibberson Conservation Area, Dauphin County
- Kings Gap State Park, Cumberland County
- Loyalsock State Forest, Lycoming and Bradford County
- Promised Land State Park, Pike County
- Shikellamy State Park, Union County
- Swatara State Park, Lebanon County
- Tiadaghton State Forest, Clinton and Lycoming County
- Tuscarora State Forest, Perry and Juniata County
- Weiser State Forest, Dauphin, Schuylkill, Northumberland County
“Spongy moth populations in Pennsylvania appear to be declining, particularly in the central part of the state, thanks to ongoing suppression efforts and the natural end of the insect’s outbreak cycle,” said DCNR Forest Health Manager Rosa Yoo. “That said, we’re still seeing hotspots and lingering populations that will be addressed in this year’s suppression program. In the northeast, populations remain a concern based on egg mass surveys conducted last fall and winter, so treatments will continue there as well. The encouraging news is that, overall, we’re seeing signs of a statewide decline, and we’re hopeful for population crashes in some areas.”
The suppression program is conducted with the goal of minimizing defoliation so that trees do not become stressed and succumb to disease, other insect pests, or drought. Aerial spraying will be conducted by two helicopters and two fixed-wing aircraft. Progress of the spray program can be followed using the interactive map on the DCNR web page(opens in a new tab), which shows the location of all the spray blocks.
Targeted sites are determined by surveys of egg masses and other indicators across the state indicating populations are increasing and have the potential to cause major defoliation.
A tree begins to significantly suffer when 30 percent or more of its leaf surface is lost, and when left untreated, heavy infestations over 2-3 consecutive years can result in tree mortality. Oak mortality leads to a loss of timber resources, a decrease in the carbon sequestered by our forests, and negatively impacts the habitat quality for many of our native species. Not only are oaks an important mast species for wildlife, but oaks host a significant number of native insects and invertebrates as well.
The applied insecticides, tebufenozide or Bacillus thuringiensis subsp. kurstaki, must be ingested by young caterpillars as they feed on emerging foliage. These products are specific to young caterpillars and must be ingested to be effective. There are no known impacts to other insect groups, including bees. These products are also subject to State and federal environmental review and are deemed safe for use and are commonly used in agriculture.
The Pennsylvania DCNR will also conduct aerial spraying in parts of Somerset, Fayette, and Westmoreland counties to protect stressed forests from Fall Cankerworm (FCW) defoliation around the same time as the spongy moth suppression program. These areas have faced repeated damage from pests and drought in recent years, making them more vulnerable. While FCW is a native insect, another year of defoliation could hinder forest recovery. Treatment zones can be viewed on the DCNR’s spongy moth interactive map(opens in a new tab).
Visit DCNR’s website(opens in a new tab) for more information on spongy moth impacts in Pennsylvania.
