Spongy moths, also known as gypsy moths, feed on the leaves of many trees such as oak, maple, apple, crabapple, hickory, basswood, aspen, willow, birch, pine, spruce, hemlock, and more. Oak is their tree of choice. Spongy moths are one of the area’s most significant and devasting forest pests. Their damage to trees can be significant and often irreversible.
What are spongy moths?
The spongy moth (Lymantria dispar dispar) is an invasive nonnative insect with larvae that feed voraciously on the foliage of many North American plants. Spongy moth caterpillars prefer oaks and aspens but do not eat conifer needles unless they are starving. Preferred hosts are concentrated in the Northeast, Midwest, and southern Appalachians and Ozarks. The spongy moth was introduced about 130 years ago near Boston and has chomped its way through New England and Mid-Atlantic regions; the current “invasion front” stretches from North Carolina across to Minnesota. (USDA Forest Service)
How do spongy moths cause damage?
When outbreaks occur, and populations are high (every 10-15 years in NY), thousands of acres of trees can be damaged. Although spongy moths do not pose a major threat to New York’s forests, they are not native, and their populations can reach high destructive (outbreak) levels.
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 2-3 successive years of defoliation (removal of leaves) without being killed. However, defoliation does reduce the vigor and resistance of the tree, and it becomes more susceptible to pests and diseases.
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. (DEC)
Local spongy moth damage, including the Capital District and Saratoga County
The Daily Gazette writes, Locally, the DEC said it’s expecting significant defoliation in Saratoga County. However, places like Clinton, Essex, Warren, and some Mohawk Valley counties will also see heavy defoliation.
“The Finger Lakes region and Allegany State Park also experienced heavy defoliation throughout,” said Severino. She said the moths are not native but have naturalized and are always in the forest. “They tend to spike in numbers roughly every 10-15 years, but outbreaks are usually ended by natural causes such as predators and disease,” she said.
The DEC mapped just under 680,000 acres of defoliation from the moth as part of its annual forest aerial survey, according to the DEC. In 2021 the moths were seen a lot in both Central and Western New York, Severino said.
While removing the moth’s egg masses in the winter won’t eradicate them entirely, it can help reduce the number of insects. If people see egg masses, they can scrape them off the tree or building into a container of detergent, which will prevent the eggs from hatching, Severino said.
What can I do to stop spongy moths from damaging my trees?
The Department of Environmental Conservation (DEC) listed options for “how to control spongy moths”:
Please note that all these options may protect individual trees or small areas, but they will not erase a local spongy moth population now or in future years. In large forested areas, manual removal is often not practical during an outbreak. DEC and its partners typically do not manage spongy moths, and treatments are usually limited to ecologically or culturally significant forests. At this time, DEC does not provide funding for controlling spongy moths on private property. Caterpillars are always being naturally controlled by birds, rodents, parasites, and diseases. Extremes in temperature can also reduce population numbers.
Squishing and Scraping
When populations are low or when you have just a few trees you want to protect, spongy moth caterpillars and adults can be killed by squishing them. Egg masses can be destroyed by scraping them off trees or other structures and dropping them in a container of detergent. We have had customers tell us they used a shop vac to eradicate large amounts on their cars, wheels, decks, and porches.
Bands, Barriers, and Traps
In late April, sticky/barrier bands may be placed around the tree’s trunk to catch caterpillars when they hatch and crawl. These bands can be bought or made at home using common household materials. View detailed instructions on making and using your own trap on the University of Wisconsin website (leaves DEC website). “Make barrier bands using duct tape and a waterproof, sticky material such as the Tanglefoot or petroleum jelly. When the bark is dry, wrap duct tape around the tree, shiny side out, pressing the tape firmly into the bark cracks to prevent caterpillars from slipping under the bands. The tape should be wrapped a few inches wide and placed around the tree trunk at chest height – about four feet above the ground.”
If you choose to use a barrier band, please check it often in case unintended wildlife pass through and replace it as necessary after rain events.
The University of Wisconsin-Madison writes, Recently, similar sticky-band trapping methods (for the invasive spotted lanternfly) have caused concerns for birds in Pennsylvania and other mid-Atlantic states. To help reduce risks to birds, consider placing chicken wire or mesh screening over the sticky bands to prevent birds from contacting the sticky surface. See this page for additional info about preventing bird contact.
In mid-June, when caterpillars are larger, replace sticky/barrier bands with a burlap trap. View detailed instructions on how to do this on the University of Wisconsin website (leaves DEC website).
How can I treat a spongy moth infestation?
Treatment can be achieved using a variety of insecticides. We have listed within this post-non-insecticide treatments you can try as well. The DEC lists the following:
- Microbial insecticides are biopesticides made from naturally occurring bacteria, viruses, fungi, or protozoans that can be targeted to a specific pest. The most common of these is Bacillus thuringiensis (Bt), which occurs naturally in soil and on plants. The Bt subspecies kurstaki (Btk) is the most appropriate for LDD control.
- Btk works best on young caterpillars, which become more resistant to treatment as they mature. When Btk is eaten, the caterpillar becomes paralyzed, stops feeding, and dies of starvation. Btk is harmless to people, animals, and plants, but does affect other young moth and butterfly larvae. A proper application will help limit exposure to non-LDD larvae.
- Chemical insecticides are contact poisons. These chemicals can have an impact on a variety of beneficial, native insects (such as bees), as well as nesting birds and other wildlife so they should be used wisely. Spraying is not effective against spongy moth pupae or egg masses, and it is less effective once caterpillars reach 1 inch long.
- Horticultural oil insecticides (aka dormant oils) are solutions refined from petroleum or plants and, when applied, smother insects or disrupt the protective coating around eggs. As with chemical insecticides, horticultural oils are non-selective but have the advantage of being relatively safe for humans and animals. The oils should be applied to egg masses in late March to early April before caterpillars emerge, and again in October to early November after adults have ceased activity.
Professional use of insecticides is recommended.
Whenever a residential or commercial property experiences an infestation, it is always wise to consult with a professional, licensed pest control company. Treatment for insects and pests such as the spongy moth requires understanding an invasive species. While these moths are not harmful to people, proper use of insecticides is critical to ensure that insecticides create no harm to people or pets.