Gypsie Moths

Asked July 10, 2018, 7:36 AM EDT

I live in Washington, MI on a very wooded 1 acre lot which is also surrounded by several other wooded lots and across the street from the north end of Stony Creek Metro Park. This past season, we have had an abundance of gypsie moth caterpillars. We have several mature oak trees, many that are over 100 years old. We have observed that some of these trees have lost significant amounts of leafs due to these caterpillars. I am concerned that they will affect the health of our trees. What do you suggest is a proactive course of action to ensure this doesn't happen.

Macomb County Michigan

1 Response

Hello, I refer you to the attached article that was written by MSU Extension educator, Robert Bricault with respect to gypsy moths. I also suggest that you refer to the msu extension article about gypsy moths which discusses possible controls for next year.

We are near the end of the time gypsy moth caterpillars will be feeding this year. Soon they will enter a stage where they change to a moth to lay eggs. Their populations go up and down in nature due mainly to a pathogen, Entomophaga maimaiga, which is a fungus that kills them during their caterpillar stage. The trouble is it was too dry in 2016 and 2017 in late spring and the fungus was not as active allowing populations to climb. This year is different with weekly rain periods allowing the fungus to grow. Though many callers are already reporting caterpillars dying (hanging straight down on trees) from the fungus this year, the feeding was serious in some areas. Trees like oaks and maples can rebound from being stipped of their leaves, while pines and spruce often do not. *Trees that were defoliated will work to put out a new set of leaves and as they do this make sure they are not also stressed by any droughts that may occur. At this stage do not let them feed on spruce and pine and watch for the dying caterpillars. If rain was timely we can have a very large die-off of caterpillars preventing them from reaching their adult stage and laying more eggs. This has happened in Washtenaw County numerous times since the late 1990's. Nature is too unpredictable but in most years we do not need to worry about them. If droughts do occur at the right time the insects population can quickly develop over the next year. See the following article which includes links for how to protect trees:

-Robert Bricault, Michigan State University Extension Horticulture Educator