Spongy Moths Return to New England


Spongy moth is the new common name for Lymantria dispar, formally known as the gypsy moth. Read more at: Spongy Moth is the New Name for an Old Pest


In New England, in the early 1980’s Spongy Moths had a dramatic surge in their population and their devastation. While most scientists expected a predictable, cyclical peak and crash, Spongy Moths damaged or killed countless urban and forest trees, and defoliated normal hosts, before turning their voracious appetites on anything growing. They began diminishing in extent of coverage here by the mid 1980’s.

In the last 30 years, New England has seen scant sign, and few hot-spot outbreaks of this devastating pest, even while it has expanded its destructive range west to Minnesota and south to Virginia.

The primary reasons believed to have limited their cyclical re-infestation have been a multitude of seldom discussed predators. Many animals, birds, bacteria, insects, fungi, and viruses contribute to the decline in Spongy Moth populations. A virus known as NPV is responsible for killing many larvae, its presence is noticeable by the caterpillars hanging partially off the trunk of trees in an inverted V.

A significant fungus, Entomophaga maimaiga has been a key pathogen holding Spongy Moth populations in check since the last serious outbreak in the 1980’s, and there have been no serious efforts to breed predators to control Spongy Moth populations. Even with the many predatory species on Spongy Moth, egg masses can contain over 500 eggs, leading to rapid explosions of damage when they occur.

Sudden Expansion

In the last few years, the population in New England has expanded rapidly, and one of the clearest correlations has been our weather. New England has experienced significant droughts for two years running, and this has inhibited the spread of the common Spongy Moth diseases, most notably the fungi, which require moisture to disperse their spores. While populations are still being impacted by animals and insects, the most serious Spongy Moth predators have been inhibited by the drought.

Risk to Trees

Single year defoliation, or partial defoliation is often of minimal long term risk to tree hosts. When defoliations occur two or more years in a row, and with the concurrent drought inhibiting the tree’s ability to refoliate due to limited energy reserves; the impact may be devastating, resulting in tree death. Trees weakened but not fully defoliated may be at risk to other diseases and insect pressures, such as Two Lined Chestnut Borer, which can kill the tree.


Regardless of whether New England experiences another sustained in-season drought in 2017, Spongy Moth larval counts are already very high in many areas. Those areas which experienced partial defoliation in 2016 can expect more severe defoliation in 2017. Those areas with complete defoliation in 2016 may experience another critical defoliation this year which could kill many already weak trees. If we experience continued spring and summer drought in 2017, we can expect populations to build, and to spread, encompassing more acres, and cites.

Treatment Options

Trunk injection with TREE-äge® or TREE-äge G4 affords applicators an effective, efficient and environmentally sound means of protecting these host species. Injection places the full dose directly into the tree’s vascular system, assuring the full dose reaches the pest, and eliminates unnecessary exposure to applicator and homeowner alike. TREE-äge and G4 also provide up to two years of protection against Spongy Moth.

There are two effective treatment times, since trunk injection can rapidly move the pest control product to the areas of feeding. Typical Spongy Moth hatch begins anywhere from late April to Mid-May dependent on factors such as temperate and precipitation, as well as soil temperatures. Treatment by injection may begin as soon as uptake conditions are favorable. It should be completed as the caterpillars increase in size, to minimize feeding damage. Ideally, they should be completed no later than May, but can be applied to a new customer to stop further damage, at even later dates.

Looking for more information? We’d love to hear from you! Or you can request a consultation from your local Regional Technical Manager.