Harrisburg, PA – After two years of aggressive and successful suppression efforts, the Department of Conservation and Natural Resources (DCNR) today announced that the beginning of targeted aerial treatment of state woodlands to combat spongy moth (Lymantria dispar dispar, formerly known as the gypsy moth) and fall cankerworm (FCW) populations poised for spring outbreaks in many sections of Pennsylvania.
After defoliating 55,286 acres in 2025, spongy moth impacts are declining. This year’s treatment will cover just over 3,100 acres — down from more than 75,000 acres last year and 227,000 the year before — reflecting the success of suppression efforts statewide.
“Pennsylvania’s forests are critical to providing clean air and water, recreation opportunities, and a sustainable timber resource,” State Forester Seth Cassell said. “Spongy moths have posed a significant threat to our native oak forests for several years and DCNR’s work to target and suppress outbreaks has worked to limit widespread tree loss. Our Bureau of Forestry’s suppression efforts are making a difference, and we remain committed to protecting these vital forested landscapes for present and future generations’ use.”
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 treatment of seven treatment blocks totaling 3,160 acres. Included will be portions of Delaware State Forest, in Monroe and Pike counties. The Pennsylvania Game Commission will not be conducting an aerial treatment program in 2026.
“Spongy moth populations in Pennsylvania continue to decline because of ongoing suppression efforts and the natural end of the insect’s outbreak cycle,” said DCNR Forest Health Manager Rosa Yoo. “We will continue to address hotspots and lingering populations that remain. The northeast is a concern based on egg mass surveys conducted last fall and winter and we are continuing to make progress in the region and are hopeful for population crashes as we have seen statewide.”
DCNR will also conduct aerial treatment across six treatment blocks totaling 5,345 acres in Forbes State Forest, in parts of Somerset and Fayette counties, to protect stressed forests from 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. More than 9,800 acres of state forestlands were treated for FCW in 2025.
The suppression programs are conducted with the goal of minimizing defoliation so that trees do not become stressed and succumb to disease, other insect pests, or drought. Aerial treatment will be conducted by two helicopters. Progress of the spongy treatment program can be followed using the interactive map on the DCNR web page, which shows the location of all the treatment 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 Bacillus thuringiensis subsp. Kurstaki (BtK), 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.
Visit DCNR’s website for more information on spongy moth impacts in Pennsylvania.
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