Managing Bagworms

Whenever pests of landscape plants in the eastern U.S. are rated, bagworms invariably land in the top ten. Bagworms are most commonly found on evergreens (Figure 1), but they will feed on deciduous hosts, too.

Bagworm feeding should be about over for the season. The insects will spend the winter as eggs in bags containing flightless female moths. A bag may contain up to 1,000 eggs. The eggs will hatch in late May or early June of the following year.

Management

Handpicking can be an effective control measure (greater than 90% reduction) for a small number of short trees. However, there is not much margin for error. As few as 9 surviving newly hatched larvae on a small evergreen can result in sufficient damage to cause a homeowner to take action. Insecticide sprays are needed for comparable control of the insects on larger or more heavily-infested trees and shrubs.

White-footed mice, European sparrows, and several species of parasitoid wasps provide effective natural control of bagworms. Parasitoids (Figure 2) are organisms that live in close association with their host and ultimately kill it. The presence of flowering forbs (herbaceous plants that are not grass or grass-like) around trees and shrubs can significantly increase attack by parasitoids; these plants provide nectar and pollen needed by biological control agents.

Figure 1. Attached bagworm bags; about 50% contain flightless female moths. (Photo: Katie Pratt, UK)

Figure 2. Itoplectis conquisitor an example of a parasitoid that attacks bagworms. (Photo: Thomas Wilson from BugGuide, Iowa State University, Department of Entomology)

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References

 

By Lee Townsend, Extension Entomologist

 

 

Posted in Landscape Trees & Shrubs