Tree-munching caterpillar alert

There have been years in the Hudson Valley when there are so many of them in the forest canopy that you can hear them munching leaves, years when the oaks of the Shawangunks have been so defoliated that the middle of summer looks like early spring. When you see tiny leaf bits drifting down on the street, you are walking under a vast horde of the creatures, eating, eating, eating.

Most of us are used to calling them gypsy moths and, in larval stage, tent caterpillars, but biologists have adopted the term “spongy moth.” Rob Cole, a forester for the DEC, held a mini press conference this spring to talk about them and the DEC's efforts to keep them under control. “Their preferred host are broadleaf trees such as oak trees, which have the ability to put out a new set of leaves after they’re defoliated," he said. "Spongy moth defoliation doesn’t kill the trees usually in one season; it will take a couple of years."

A post on the NYS DEC website explains, “Spongy moth caterpillars eat young, tender leaves in the spring. Deciduous trees (trees that lose their leaves each fall) can regrow a new set of leaves by July and can usually withstand two to three successive years of defoliation without being killed. However, defoliation does reduce the vigor and resistance of the tree … death can occur when other stresses such as disease or other insect outbreaks attack trees in the same year. When populations of spongy moths are very high, or when oak and other preferred trees are limited, they will even eat evergreen species including pine, spruce and hemlock. Evergreens do not regrow leaves as easily as deciduous trees and can die as a result of complete defoliation.” (June 25, 2021)

Sounds grim, but spongy moth populations wax and wane. “Typically spongy moth outbreaks will last two to three years and we can go 10 to 15 years in between,” said Cole. Forests will survive, though individual trees may die. Animals that eat lots of acorns – squirrels, chipmunks, black bears – will suffer, at least in the short term.

“ Last year, we had a couple of areas hit pretty hard,” said Cole. “The eastern Adirondacks along the Northway from Saratoga County all the way up to Clinton County, the Mohawk Valley, and then the Finger Lakes were defoliated pretty bad for a second year in a row … We’re expecting this year to be another big year of defoliation.”

Because of these repeated outbreaks, the DEC made the decision to spray a pesticide on some state forest land and state parks in May. “Those areas were chosen because they contain high value ecosystems where rare, threatened or endangered animals and plants live and need that ecosystem to survive,” said Cole. “The product that DEC is using for its treatments this year is called Gypcheck, which was developed by the U.S. Forest Service. It’s a virus that’s specific to the spongy moth. In areas where it’s applied it is considered very effective.” (Gypcheck is designed to target spongy moths alone, and doesn’t affect any other insects or animals.) “Spongy moth has a number of natural predators [but] this year, we decided, because last year was such a heavy defoliation year, that we couldn’t risk being defoliated again. However, outbreaks usually only last two to three years, so we don’t treat regularly because the outbreak will end on its own.” Thankfully, shrews, white-footed mice and some birds will eat the moths and even their larvae, which are not easy to digest.

This year, so far the worst infestations are again happening to our north, in the Adirondacks, Capitol District, and in western NYS. That said, local resident (and BSP cartoonist) Bruce Sconzo reported recently, “I have been out killing them daily on my apple trees.” If your trees are being eaten by caterpillars, there are ways to help them. Forester Cole again: “A homeowner, if they have spongy moth on their property, there are a few things they can do, such as using sticky bands or burlap bags wrapped around the trunks of their trees to catch the spongy moths as they crawl up and down the tree. If you’re a larger landowner, aerial applications [of a targeted pesticide] are available through a certified applicator.”

For more information about spongy moths and how to control their numbers, go to dec.ny.gov, or search online for "NYS-DEC spongy moth" to get directly to the DEC info page.