Spongy Moth (Lymantria Dispar)
Since 2021, the City has experienced an increase in spongy moth (formerly known as gypsy moth) populations. 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 implemented an aerial spray of the core impacted area in the Forest Preserve located in the Dee-Devon Woods area, commonly referred to as Southwest Woods in spring of 2022. While control of the pest was successful in the treatment area, the pest has naturally spread into adjacent residential properties resulting in defoliation of mature oak trees and nuisance caterpillars impacting the quality of life of our residents.

In 2023, aerial treatments were performed over Southwest Woods in areas adjacent to the Forest Preserve. Treatment areas were determined by the number of egg masses identified during the winter survey as well as the location of defoliated trees the year prior.

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

July 2023 Update
Spongy moth aerial treatments were completed in early June. Post-treatment surveys indicated effective moth population control, minimal leaf feeding, and no substantial signs of spongy moth present.

Forestry staff will monitor spongy moth populations in subsequent years to see if applications will be warranted in the future. One thing to consider is that we are in our third year of this spongy moth wave. In most cases, spongy moth populations naturally decline in 1-3 years of an infestation’s peak due to naturally occurring build up of disease (virus and fungus) and predators. This pest is unfortunately here to stay and generally infested areas will experience outbreaks every 10-15 years. Aerial treatments were also performed in the 1980’s and early 2000’s and were effective in reducing the pest.

What should I do about trees on my property?
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. Treatment should take place in early spring.

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.