This Summer, the East Coast again battled the spongy moth*, but the damage is spreading. The destructive pest also did damage in the upper Midwest, where a drought worsened the problem. Officials in Minnesota laid more than 20,000 traps after a record outbreak last Summer. The invasive pest, which can damage more than 300 tree species, has spread to nearly half of U.S. states.
The insects do the most damage in their caterpillar stage in early Summer, when they can defoliate and kill key U.S. trees like oak, willow, apple, birch, pine, and dozens of others. In August, the now-adult moths laying masses of 100 to 600 eggs each. The eggs are protected by a light-colored, almost hairy covering. They are often on tree trunks, but moths also deposit them on the side of buildings, signs, trailers, or other outdoor surfaces.
So far, inspectors have found moths in counties in Connecticut, Delaware, the District of Columbia, Illinois, Indiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, Vermont, Virginia, West Virginia, and Wisconsin.
The Animal & Plant Health Inspection Service maintains an updated list of US counties that are under quarantine against spongy moth. Green Industry professionals should be aware of some rules associated with the quarantine. It’s forbidden for anyone to move certain articles between quarantined and unquarantined counties without an inspection and a permit. These include: trees without roots (like Christmas trees); trees with roots; shrubs with roots and persistent woody stems (unless they are greenhouse grown throughout the year); logs, pulpwood, and bark and bark products.
An APHIS spokesperson explained that although there are no specific rules that apply to landscapers, everybody must follow the quarantine requirements for the pest in quarantine areas.
What To Do
The most effective active interventions for L. dispar involve aerial spray applications of chemical and biological insecticides. Pros most commonly use Bacillus thuringiensis subspecies kurstaki (Btk), a bacterium that kills caterpillars upon ingestion, and tebufenozide. However, both of these are most effective when used early, such as in May.
Penn State Extension suggests monitoring all trees for damage and defoliation. Trees often recover the next year if another infestation can be avoided. Manually removing egg masses or trapping the insects can help, but it’s impractical for large or multiple properties. The most effective plan this year? Maintaining overall tree health, since healthy, unstressed specimens are better able to fight off pests and recover from damage.
*Formerly known as the gypsy moth.
Opening photo credit: Adobe Stock by ondreicka
For more on the spongy moth: