What is an emerald ash borer?
An invasive beetle from Asia that feeds under the bark of ash trees, disrupting nutrient flow and killing trees within a few years of infestation.
The emerald ash borer (Agrilus planipennis) is a metallic green beetle native to Asia that has devastated ash tree populations across Westchester County and the Hudson Valley since arriving in North America in the early 2000s. The pest arrived in infected wooden packing material and has spread steadily throughout the region, now present in virtually every Westchester town. Ash trees have no natural resistance to this insect.
Larval borers tunnel beneath the bark, creating S-shaped galleries that sever the vascular tissue carrying water and nutrients through the tree. Infested trees typically decline within two to four years of initial attack. Signs of infestation include D-shaped exit holes (about 1/8 inch wide) in the bark, bark splitting and peeling, crown dieback starting at the top, and loss of branches. Woodpeckers may strip bark searching for larvae, leaving the trunk looking shredded.
The beetle kills all species of ash trees found locally, including white ash, green ash, and black ash. Since ash is common in Westchester yards and forests, the borer has driven significant removal demand. Once a tree is infested, removal becomes the primary option. Property owners often hire arborists and tree service professionals to remove dying or dead ash trees safely and prevent branch failure that threatens structures or people nearby.