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Eastern tent caterpillars are perhaps best known for the web tents that occur in the crotches and forks of branches in spring and early summer. Even if they cause c omp l e t e defoliation, healthy trees readily recover. Eastern tent caterpillars are a native species that are attacked by a plethora of natural enemies, including birds and various insect predators, so outbreaks are periodic and short-lived and damage is generally considered aesthetic rather than a health threat to most trees.
The primary concerns for tent caterpillars are productive fruit trees and breeding horses. Eastern tent caterpillars preferentially feed on fruit trees and wild cherry but occasionally feed on other deciduous shrubs and trees. When caterpillars are abundant, they can completely defoliate an infested tree. Accidental consumption of wandering caterpillars has been linked to mare reproductive loss syndrome in horses, so horse owners with breeding mares should be cognizant of the host trees around horse pastures (like the common wild cherry tree often present in fencerows) and outbreak status of caterpillars.
Eastern tent caterpillars have one generation per year. Caterpillars hatch out in early spring. When caterpillars mature in early summer, they migrate away from the tent to find a protected place to spin a cocoon and pupate. This can be cause for concern for homeowners when they encounter large numbers of wandering caterpillars. However, mature caterpillars in this stage do not feed and are no longer a threat to plants.
Healthy deciduous trees can withstand total defoliation multiple years in a row without long-term detrimental effects, so it is not recommended to attempt to control caterpillars in natural forest settings. For ornamental trees, one option is to keep trees healthy and do nothing. If control is warranted, caterpillar density can be reduced by pruning out egg masses during the winter before they hatch and manually removing silk tents using a stick or other implement and disposing of them. Caterpillar tents should never be burned with fire. Besides potential danger to nearby structures, the fire will cause more damage to the tree than the caterpillars could.
If manual removal is not possible, young caterpillars can be controlled using Bt (bacillus thuringiensis) or horticultural oil. Older caterpillars can be controlled using broad spectrum insecticides – there are many products labeled for caterpillar control on ornamental trees – but this should only be done in rare circumstances and as a last resort given the considerations mentioned above.
The content of this week’s column is from an Extension publication from Penn State University. A complete printed copy of the article with excellent photos is available from the Rockbridge County Extension Office for by email to stanleyt@ vt.edu.
