The spongy moth caterpillar (Lymantria dispar) is a non-native insect that defoliates temperate deciduous forests in the United States, and has created challenges for forest landowners and managers for a century. The degree of spongy moth’s effect on our hardwood forests varies based on several factors, including overall stand health, species composition, recent stress from other pests and drought, crowding, inter-stand competition, and developmental stage of the woodlot. Interestingly, this year we’ve seen a lull in spongy moth impact in our region.

spongy moth (Lymantria dispar dispar)

A bit of history: Over 100 years ago the caterpillars were brought to the United States for research in silk production. Now their sole purpose is to defoliate our trees. Persistent defoliation poses a risk to overall tree health. So why might we be getting a break from the infestation?

  • Natural controls: Ample rainfall, which has allowed the natural controls (fungus and virus) to more effectively reduce the spongy moth caterpillar numbers. In the recent past, dry weather conditions might have limited the activity of these natural controls, leading to the outbreak.

  • Natural cycles: Spongy moth caterpillar outbreaks are cyclical. This means that once the current outbreak comes to an end, it is expected that there won’t be another outbreak for a few years.

  • The combination of natural controls, some help from a wet spring, and the cyclical nature of the caterpillar outbreaks resulted in lower populations and impacts this year.

In the east, much of the land is privately-owned, making it difficult to coordinate landscape-scale aerial spraying programs to control spongy moth. A couple actions you can take are to walk your woods each Autumn and look for spongy moth egg masses on the underside of large limbs, particularly in the upper bole of the tree. If you have high egg mass counts on the lower portion or trunk of the tree, you likely will have significantly higher counts in the upper portions of the tree. Chances are, if you see dozens of egg masses per tree in the Autumn, your stand is at risk of some level of defoliation during the following Spring.  So, winter is a great time to contact your local, independent forestry consulting firm or local state forestry agent, and ask how you and your neighbors might coordinate and explore options for control during the coming months.

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