Spongy Moth (formerly Gypsy Moth)
Lymantria dispar
Range: Northeastern and Great Lakes United States and eastern Canada, spreading south and westSee it on the alert map
Symptoms & signs
- Heavy spring defoliation, sometimes stripping entire crowns bare
- hairy caterpillars with five pairs of blue and six pairs of red dots down the back
- buff-colored fuzzy egg masses on bark, branches, and structures
- frass (droppings) raining down
- repeated defoliation weakens and can kill trees, especially oaks
Treatment & management
- Scrape or oil egg masses in winter
- Apply Btk (Bacillus thuringiensis kurstaki) to young larvae, or other registered insecticides for larger larvae
- Burlap trunk bands trap caterpillars by day
- Area-wide programs use the Entomophaga maimaiga fungus and NPV virus
- Keep host trees vigorous with water and mulch
Host species
Northern Red OakQuercus rubraWhite OakQuercus albaPin OakQuercus palustrisBur OakQuercus macrocarpaAmerican BeechFagus grandifoliaQuaking AspenPopulus tremuloidesPaper BirchBetula papyriferaRiver BirchBetula nigraAmerican Linden (Basswood)Tilia americanaWillow OakQuercus phellosScarlet OakQuercus coccineaSwamp White OakQuercus bicolorChestnut OakQuercus montanaWater OakQuercus nigraBlack CherryPrunus serotinaShumard OakQuercus shumardiiPost OakQuercus stellataChinkapin OakQuercus muehlenbergiiNuttall OakQuercus texanaValley OakQuercus lobataOregon White OakQuercus garryanaMockernut HickoryCarya tomentosaPignut HickoryCarya glabraSouthern Red OakQuercus falcataBlack OakQuercus velutinaCalifornia Black OakQuercus kelloggiiEnglish OakQuercus roburSawtooth OakQuercus acutissimaOvercup OakQuercus lyrataBitternut HickoryCarya cordiformisShellbark HickoryCarya laciniosaBigtooth AspenPopulus grandidentata
Common questions
Will one year of defoliation kill my oak?
Usually not — healthy hardwoods can refoliate after a single defoliation. It is repeated defoliation over consecutive years, often combined with drought or root rot, that kills trees.
When should I treat for spongy moth?
Target the young caterpillars in mid- to late spring, when Btk and other treatments work best. Scraping egg masses over winter also reduces the next season's population.
Related pests
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