The Department of Conservation and Natural Resources has started its targeted aerial treatment of state woodlands to combat spongy moth and fall cankerworm populations in many sections of Pennsylvania.
These treatments aim to prevent spring outbreaks of the insects.
DCNR officials say the 2026 treatment plan marks a significant reduction in affected acreage compared to previous years, reflecting successful suppression efforts.
After defoliating 55,286 acres in 2025, spongy moth impacts are declining. This year’s treatment will cover just more than 3,100 acres, down from more than 75,000 acres last year and 227,000 the year before.
State Forester Seth Cassell says that spongy moths have significantly threatened native oak forests for several years, but the treatments have helped protect them.
“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,” he said.
The DCNR will oversee spongy moth treatment across seven blocks, including portions of Delaware State Forests.
Spongy moths feed in their larval stage, typically hatching from mid- to late April in southern Pennsylvania and early to mid-May in the northern part of the state.
Trees most affected by the spongy moth include oak, apple, sweet gum, basswood, birch, aspen and willow. DCNR’s Bureau of Forestry experts indicate that the state’s oak tree stands are particularly vulnerable to these infestations.
The DCNR will also conduct aerial treatment for fall cankerworms, covering 5,345 acres across six treatment blocks in Forbes State Forest, located in parts of Somerset and Fayette counties.
This treatment, happening around the same time as the spongy moth program, aims to protect stressed forests from defoliation. These areas have faced repeated damage from pests and drought in recent years, making them more vulnerable. While the fall cankerworm is a native insect, another year of defoliation could prevent forest recovery.
The suppression programs aim to minimize defoliation, preventing trees from becoming stressed and succumbing to disease, other insect pests or drought.
Aerial treatment will be conducted using two helicopters. Targeted sites are selected based on surveys of egg masses and other indicators across the state, identifying areas where populations are increasing and have the potential for major defoliation.
The applied insecticide, Bacillus thuringiensis subsp. Kurstaki (BtK), must be ingested by young caterpillars feeding on emerging foliage. This product is specific to young caterpillars, requires ingestion to be effective and has no known impacts on other insect groups, including bees.
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