Agriculture agencies investigate spongy moth

The Virginia Department of Forestry (DOF) and the Virginia Department of Agriculture and Consumer Services (VDACS) are joining forest health professionals across the Commonwealth to monitor the invasive spongy moth (formerly known as the Gypsy Moth). Long established in Virginia, the caterpillar with a voracious appetite favors oak trees but will also feed on many types of hardwoods. In areas with large infestations, the caterpillars can strip entire mountainsides of foliage.

In 2024, the most severe damage has been observed in the Shenandoah Valley and the mountains west of Harrisonburg and Staunton. During an aerial survey in June, DOF Forest Health staff observed damage to more than 60,000 acres. While spongy moth caterpillar feeding can remove all leaves from a tree, recovery is possible. Most trees typically survive one or two years of defoliation. Unfortunately, if a tree is weak or damaged to begin with, spongy moth feeding will lead to tree decline.

In early May, federal and state agencies treated select public areas with aerial biopesticide applications to suppress spongy moth populations. DOF surveys have recently observed a decline in spongy moth populations following the biocontrol measures, a hopeful sign for our forests. Spongy moth caterpillars are also often susceptible to both an Entomophaga fungus and nucleopolyhedrosis virus, which can cause mass population crashes.

“While spongy moth infestation is severe this year, it’s encouraging to see biocontrols killing caterpillars in impacted areas,” said Forest Health Program Manager Lori Chamberlin. “These countermeasures can greatly reduce populations, resulting in less damage to our forests next year.”