Spongy Moth (Gypsy Moth) Control

Spongy Moth (Gypsy Moth) Control in Rockford, IL & Southern Wisconsin

The spongy moth — formerly known as the gypsy moth — is one of the most destructive invasive insects in North America. Its caterpillars can completely defoliate susceptible trees in a single season, and repeated defoliation over two or more consecutive years can kill even large, established hardwoods. Tree Care Enterprises provides targeted monitoring, treatment, and follow-up to protect your valuable trees throughout Winnebago County, Walworth County, and the greater Stateline region.

The Threat to Regional Trees

Spongy moth caterpillars feed on over 300 tree species, but they strongly prefer oaks — among the most important and highest-value trees in northern Illinois and southern Wisconsin landscapes. Birch, willow, cherry, apple, and hawthorn are also highly susceptible. Defoliated oaks that are already under stress from drought, soil compaction, or nearby EAB pressure are particularly vulnerable to fatal decline following repeated outbreaks.

The pest is now established across parts of northern Illinois and southern Wisconsin. Populations fluctuate significantly year to year and can crash naturally from nucleopolyhedrovirus or from the naturally occurring fungus Entomophaga maimaiga, but high-value trees in outbreak areas should not be left unprotected when populations are building.

Identification and Monitoring

Early detection is critical. Spongy moth produces distinctive egg masses — buff-colored, 1–2 inch fuzzy patches typically found on tree bark, fences, and outdoor furniture from fall through early spring. Caterpillars hatch in April through May and feed heavily through late June. Each caterpillar passes through multiple instars (growth stages), and treatment is most effective when caterpillars are young (early instar, approximately ½–1 inch in length). Our ISA Certified Arborists — John Richards (IL-0027A), Doug Edwards (IL-0505A), Matt Richards (IL-9831A), Jeremy Montana (IL-4690A), and Pete Montana (IL-4689A) — conduct site evaluations and egg mass surveys to gauge infestation severity before recommending a treatment approach.

Treatment Options

• Btk (Bacillus thuringiensis var. kurstaki): A biological insecticide derived from a naturally occurring soil bacterium. Btk is highly targeted to caterpillar species and has minimal impact on beneficial insects, birds, or mammals. Applications must be timed to coincide with early caterpillar hatch. Highly effective when properly timed.
• Diflubenzuron (Dimilin): An insect growth regulator that prevents caterpillars from molting. Applied as a foliar or bark spray, it provides effective coverage over large canopy areas.
• Trunk Injection (Emamectin Benzoate / Tree-Äge): For high-value specimen trees where foliar spray isn't practical, trunk injection provides systemic protection and multi-year control — the same active ingredient used for EAB treatment.
• Egg Mass Removal: In smaller infestations, mechanical removal and destruction of egg masses before hatch (November through April) can meaningfully reduce the following season's population.

Post-Defoliation Tree Care

Oaks and other deciduous trees can typically releaf once in early summer after defoliation, but doing so depletes stored carbohydrate reserves. Trees that are defoliated and also dealing with drought, compaction, or other stressors may benefit from post-event deep-root fertilization, supplemental watering, and a plant health care assessment to strengthen them before the following season. Our arborists can coordinate spongy moth treatment with broader PHC programs when needed.

Tree Care Enterprises holds TCIA accreditation and has been treating spongy moth and other forest insect pests in the Rockford and Lake Geneva regions since 1978. If you've noticed egg masses, caterpillar activity, or unexplained defoliation on your oaks or birches, call 815-965-5757 to schedule an evaluation. Early treatment makes the difference.