The gypsy moth (Lymantria dispar), an invasive species native to Europe, has been making a significant appearance this year, as recreational users on the Allegany National Forest (ANF) have reported seeing abundant populations of gypsy moth caterpillars, primarily across the northern half of the Bradford Ranger District.
“The DCNR (Pennsylvania Department of Conservation and Natural Resources), Bureau of Forestry has received similar reports about gypsy moth caterpillars defoliating trees on private lands in the region,” said Cornplanter District Forester Cecile Stelter in a recent press release.
Ken Kane, president and owner of Generations Forestry, has seen firsthand how the gypsy moth caterpillars have affected the private forestry industry. Kane said Generations Forestry actually predicted the defoliation last August, but unfortunately, the company was unable to find enough private landowners to participate in a private spray program.
“We attempted to put a private spray program together, however in order to do it economically, it would’ve taken about 4,000 acres,” he explained. “We couldn’t come up with enough land owners that would come into the program, primarily because people didn’t see it.”
Kane said this year they’ve noticed significant defoliation up on the ridge on the McKean/Warren County line and the north hill above Smethport, as well as in portions of Potter County, Cameron, Elk and especially Warren County.
Generations Forestry will be monitoring the gypsy moth situation and gathering data throughout the year, with hopes that the information will persuade private landowners to participate in a private spray program next spring.
“By presenting the data to landowners, it should be easier to build a spray program for next year,” noted Kane.
Additionally, he discussed the financial benefits of spraying versus not spraying.
“If you had a forest that was susceptible that had about 5,000 board feet of oak per acre, the growth on that oak would be about 3 percent,” he explained. “So 3 percent of 5,000 board feet would be somewhere around 150 board feet per acre. So if you were to invest $30 an acre to spray to make sure you didn’t lose growth for that year, it would be very cost effective for you to spray.”
Although a private spray did not occur, according to Tim Tomon, Forest Health Program Specialist for the PA Bureau of Forestry, the Forest Service and the DCNR Bureau of Forestry were able to complete several aerial suppression treatments across 203,569 acres of state forests, parks and game lands across Pennsylvania. Such spray treatments are performed in spring when the caterpillars are small and before extensive damage from defoliation occurs.
Gypsy moth caterpillars prefer oak trees, though they will also feed on various other trees and shrug species, such as alder, apple, aspen, basswood, birches (gray, white and river), boxelder, hawthorn, larch and witch hazel.
There are many different factors that play into the gypsy moth population, as they are known for occurring in boom and bust cycles.
Two diseases have caused prior outbreaks to collapse by affecting older gypsy moth populations. One such disease is nucleopolyhedrosis virus (NPV), which is naturally present in gypsy moth populations at high densities.
The other disease is a fungus called Entomophaga maimaiga, which is native to Japan and was introduced to the United States in the 1990s as a biological control for the gypsy moth. The weather can play a role in the effectiveness of the Entomophaga miamaga, as the spores need moisture and high humidity to germinate. Regular rain and warm temperatures in May and June can aid the germination during gypsy moth outbreaks.
The good news is there are steps the average person can take on their own property to mitigate the damage caused by gypsy moth caterpillars.
According to Penn State Extension, the signs to look for when assessing for gypsy moth caterpillars are:
— Defoliation of branches or entire tree (at first noticeable at the top of the tree)
— Tan egg masses on the trunk or underside of large branches
— Gypsy moth caterpillars up to 2½ inches (63–64 mm) long
— Reddish-brown pupal cases hanging from trunk
— Adult moths in midsummer
Michigan State University Integrated Pest Management offers advice on home-based efforts to mitigate the damage. The first is scraping egg masses into a container filled with soapy water or by burning or burying the egg masses. Do not leave eggs or bits of egg mass on the ground, as those can often hatch the following spring.
Some individuals use Bt (Bacillus Thuringiensis var. kurstaki) to protect landscape trees and shrubbery from defoliation. It’s applied by spraying leaves one to two weeks after the eggs have hatched. Bt is not harmful to humans, birds, fish or other animals. Additionally, it has little effect on beneficial insects such as parasitoids, pollinators and predators. Bt can be sprayed by oneself or a professional arborist tree care service. For large trees, it’s recommended to contact a professional who has the proper equipment to get the Bt deep into the canopy where the caterpillars feed.
In addition to Bt, there are several other conventional insecticide products that can be used to control the caterpillars on landscape trees. Spraying such insecticides can be effective, but will likely affect non-target species, such as pollinators, predators and parasitoids.
For trees that have already been heavily defoliated, there are steps that can be taken to help keep them healthy, such as watering them once a week during dry periods in the summer and fall. To do this, run a hose slowly near the base of the tree a few hours once a week or place a sprinkler between the trunk and the drip line of the canopy. Place an empty container near the sprinkler and let the sprinkler run until there’s an inch of water inside the container. Additionally, be cautious with lawn mowers, weed wackers, snow shovels and other equipment, as wounds can increase the risk that trees will be affected by disease.
