This press release was first published by the Delaware Forest Service.
The Delaware Forest Service encourages landowners and other Delaware residents to scout for any spongy moth (formerly known as gypsy moth) egg masses this coming spring.
“Homeowners and woodland owners, especially in last year’s outbreak areas around the Cypress Swamp and Nanticoke State Wildlife areas, should be aware of what spongy moth (formerly “gypsy” moth) egg masses look like, and roughly how many are in their neighborhood,” said Delaware Forest Health Specialist Bill Seybold. “They are most likely to be found on the trunks and undersides of main branches of both hardwood and pine trees, though they feed on the leaves of oaks and some other hardwood trees a bit later in May and June. The female moths laid egg masses in July and August. The insect has survived the winter in this egg mass stage. Small, dark caterpillars about 0.25” will emerge from these egg masses, most likely in mid-April when temperatures have warmed enough. They are challenging to spot casually at this early stage; however, wary landowners can probably find them if they know and monitor nearby egg masses’ conditions as the weather warms up.”
If spongy moth caterpillars or defoliation have been spotted during the growing season (previous June through August), residents should consider going out on a dry day between now and late April to look for egg masses on trunks. Any egg masses found should be scraped into soapy water. Fresh egg masses are yellow-brown, intact, and firm to the touch. More information on how to predict how much defoliation to expect next May and June, can be found at the Delaware Forest Service – Forest Health page.
According to Seybold, once caterpillars have emerged from the egg masses, besides contacting a licensed pesticide applicator, some do-it-yourself strategies can be used to lessen the leaf defoliation that individual trees suffer. The primary strategies are sticky barrier bands around trees for the earlier, smaller stages of caterpillars, and burlap or cloth collection bands around tree trunks in later May to early June when the caterpillars are much larger. These methods are NOT practical for anything more than a few trees and require a lot of maintenance. Contact the Delaware Forest Service for details on how to apply these methods.
In the spring and early summer, spongy moth caterpillars feed on the leaves of many different tree species, especially oaks. Healthy trees often do not die from one year of defoliation; however, severe defoliation for two continuous years or more is more of a concern for the tree’s health. Evergreen trees are rarely defoliated.
The most common option for deciduous forests of about 20 acres or larger is to aerially spray the young larvae, usually in May, when the leaves of the oak trees have elongated at least an inch, and the larvae are in the first and second stages of growth.
If you have a block of forest that is under threat from heavy spongy moth defoliation, you may choose to do an aerial application from a licensed applicator. Healthy caterpillars from unsprayed adjacent woodlands will drift into smaller areas and cause almost the same amount of damage as if not sprayed. Typically, the decision to aerially spray must be made by January, due to the need to contract a spray job with the small number of licensed applicators in Delaware. Forest landowners who suspect they may have enough egg masses per acre to warrant a privately contracted spray may call the Forest Health Specialist at (302) 698-4553 for technical assistance and a list of aerial applicators. Currently, the Delaware Department of Agriculture does not have an organized spray program with financial assistance.
Control methods can be found by an internet search of “Control of Spongy Moth;” however, not all websites have the same level of professional review before they are published. The Delaware Forest Service strongly recommends using a website created by a University Extension system, or a federal or state government entity.
The first image (credit: Wisconsin Department of Agriculture) pictures high-density spongy moth egg masses. The second image (credit: USDA Forest Service) pictures newly hatched first-instar caterpillars. Visit USDA’s Animal and Plant Health Inspection Service’s Pest Identification page to learn how to identify the spongy moth in its egg mass, larval, pupal, and adult moth stages.