Spongy Moth (Lymantria Dispar)

Spongy Moth (Lymantria Dispar)

Spongy Moth (Lymantria Dispar)
In 2021, the City  experienced an increase in spongy moth (formerly known as gypsy moth) populations in concentrated areas of the city. Spongy moth is an invasive pest that is capable of feeding on over 300 different species of trees and plants, however, their preferred species are oaks. While healthy trees can withstand and recover from mild defoliation, stressed trees are more likely to succumb to high levels of defoliation during these outbreak years.

Based on the severity of the outbreak in 2021, the City conducted an aerial spray of the core impacted area located in the Dee-Devon Forest Preserve area, commonly referred to as Southwest Woods in spring of 2022. While control of the pest was successful in the treatment area, the pest had naturally spread into adjacent residential properties resulting in defoliation of mature oak trees and nuisance caterpillars impacting the quality of life of our residents.  This triggered a winter egg mass survey which indicated a very high population of spongy moth present resulting in additional aerial treatments in spring of 2023.

2023 Spongy Moth Aerial Treatment Map
Frequently Asked Questions (Spongy Moth & Btk)

February 2024 Update
Visual surveys were conducted in summer 2023 to determine effectiveness of the treatment and feeding pressure on trees in both treated and non-treated areas. These surveys indicated extremely effective caterpillar control and minimal leaf feeding pressure. Additional winter surveys indicated that spongy moth pressure was expected to remain low in 2024.  Effective treatments and the build up of natural disease is likely contributing to the declining spongy moth population which usually occurs within 1-3 years of an infestation's peak. 

While there still may be isolated concentrations of spongy moth present in the city, overall, there has been minimal feeding pressure on the city's trees and a noticeable decline in the abundance of caterpillars. Therefore, the City will not be conducting aerial treatments for spongy moth in 2024.  

What should I do about trees on my property?

Check out the Illinois Department of Agriculture's webpage for additional spongy moth information and homeowner recommendations. 

Keeping a tree healthy is the best defense against spongy moth caterpillars. Properly mulching and feeding trees along with making sure they receive enough water (1 inch per week when dry) will help keep your trees healthy and viable.

If you have experienced moderate to severe defoliation, treatment might be a good option. Many local tree care companies deliver safe and effective treatments for trees on private property. Tree-äge® is one product used by tree care professionals to control spongy moth and it is the same product we use to treat ash trees for emerald ash borer. The product is simply injected into the tree’s vascular system in the most effective and environmentally responsible way possible. As a preventative treatment, it can protect the entire canopy for up to two years so in many cases one treatment is all that is needed since spongy moth populations naturally decline within 1-3 years. 

Note: Injections are performed as a preventative treatment and should take place in early spring before caterpillar emergence. Once caterpillar feeding begins, treatments will not be effective.

For more information, please visit the follow resources:
Illinois Department of Agriculture (IDA) - Lymantria Dispar/Spongy Moth
Michigan State University Extension - Spongy Moth IPM
University of Wisconsin-Madison - Spongy Moth in Wisconsin
United States Department of Agriculture (USDA) - Gypsy Moth
United States Department of Agriculture (USDA) - Leaflet 162 - Spongy Moth
National Slow the Spread Program

Btk Information
Btk: One Management Option for Spongy Moth - Michigan State University 
Foray 48B - Valent BioSciences - Product Label
Foray 48B - Valent Biosciences - Safety Data Sheet

If you have any questions, or would like more detailed information, please contact the Park Ridge Forestry Division at 847-318-5231.