Bagworms Are An Unsightly Pest

Bagworm (Thyridopteryx ephemeraeformis (Haworth), is a serious insect pest of many ornamental shrubs and trees in the eastern half of the United States. If left unchecked, they can defoliate a plant quickly and if nothing else, their cocoons are unsightly in any garden.

Host plants for Bagworms include Conifers, especially arborvitae, cedar, juniper, and pine are the most frequently damaged host plants. Deciduous trees such as sycamore, maple, locust, boxelder, and linden are also attacked but they are not seriously damaged. They have also been seen on Cherrylaurels.

The Bagworm itself is actually the larval or caterpillar stages of moths. After hatching in early June, they immediately spin a cocoon-like bag to which are attached pieces of leaves from the plants they feed upon. Bagworms complete their growth in August or early September. At this time, the 1-2 inch long bags are permanently attached to plant twigs by means of tough silken threads. In late summer they pupate inside the bags and then transform into moths, mate, lay eggs and die. The new eggs hatch in the next spring and the cycle starts over again.

How To Treat For Bagworms

Mechanical Control

The simplest way to control Bagworms is to pick off the cocoons and discard them. This must be done before the eggs hatch in June. When too many plants are involved, to make hand picking practical, sprays are in order.

Biological Control

Bacillus thuringiensis, often called Bt, is a type of bacteria that only kills certain insects and does not affect humans or animals. Bt must be applied between mid-June and mid-July because it works well only on young bagworms. This biological control material is commercially available under a number of product names and is sold in local hardware stores and garden centers.

Chemical Control

If chemical control is absolutely necessary, a registered insecticide should provide control if applied thoroughly to all infested plant foliage after July 15. Check the label on the pesticide to be sure bagworm and the type of plant you wish to spray are listed.

CAUTION! Always follow label instructions when using pesticides. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.

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