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The Commons
Life and Work

Forest tent caterpillar damage expected again in 2018

Originally published in The Commons issue #461 (Wednesday, May 30, 2018).


Forest tent caterpillars have hatched, according to forest health specialists from the Vermont Department of Forests, Parks and Recreation. These insects are expected to cause defoliation again this summer in maple forests in northern and southern Vermont.

Forest tent caterpillars will continue feeding through June. They prefer sugar maple and ash but can feed on other tree species as well. In 2017, forest tent caterpillars defoliated 60,000 acres of forestland, affecting every county in the state.

Defoliation reduces tree growth and can have an impact on maple tapping for syrup production. However, most trees will survive despite such setbacks, even if they are defoliated several years in a row.

Forest tent caterpillars are native to much of North America, including Vermont. Natural enemies of the caterpillar have brought previous outbreaks to an end before significant tree mortality occurred.

Forest tent caterpillars are mostly blue, with white keyhole-shaped spots. In spite of their name, they do not create “tents” of webbing like their close relatives, the eastern tent caterpillars.

Instead, they can be spotted feeding directly on leaves, resting in masses on the bark, and in mid-summer their cocoons can be seen rolled up inside leaves.

Over the past winter, the Department of Forests, Parks and Recreation conducted surveys of forest tent caterpillar egg masses in 70 sugarbushes to predict the risk of defoliation in 2018.

Thirty of the survey locations are at risk of defoliation this spring. Based on these surveys, landowners will be having 13 of these sugarbushes, about 4,000 acres total, treated with a certified-organic biological insecticide, Btk, (Bacillus thuringiensis var. kurstaki), to protect them from defoliation.

These aerial treatments will be dependent on weather and growth stage. To learn more, visit fpr.vermont.gov.

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