Pest Alert: Bagworms are on the move

The common bagworm is found from all along the eastern half of the United States. They most commonly attack arborvitae, juniper, cedar, and Leyland cypress. They occasionally occur on broadleaf trees and shrubs.

You can easily recognize this insect by the tapering grey to tan silk bags it produces and attaches to its host plant. Bags are about 1 1/4 inches. Some of the needles or leaves of the plant are usually woven into the bag. If the bags contain caterpillars, they are not firmly attached to the plant and they move it some they can get to more food. When the insects pupate, they use strong silk to attach the bag to the plant.

Adult females are wingless and never leave the bag. Eggs, as many as 500, are deposited inside the bag. This is how this pest overwinters. In the spring, newly hatched larvae either remain on the original plant or spread to other plants by ballooning on a silken parachute.

The feeding caterpillars damage the host plant by defoliating it. When only a few caterpillars are present, defoliation is negligible, but heavy infestations can result incomplete, or severe defoliation of individual plants. In severe cases you end up with a defoliated plants covered with bags. These plants usually die.

Because of this insect’s limited mobility, infestations are often localized, and you can hand pick bags before eggs hatch in the spring. It is easier to remove bags of larvae than pupal cases or egg cases, which are attached to the plant with strong silk. These often have to be cut away with scissors or pruning shears.

You can control this pest with foliar insecticide sprays, but choose your treatment carefully. Chemical controls:

carbaryl - Sevin

permethrin - Hi Yield Garden, Pet, and Livestock spray or Bonide Eight

cyfluthrin – Bayer Advanced Garden Power Force Multi-Insect Killer

cyhalothrin -Triazide Soil and Turf Insect Killer

Spinosad - Fertilome Borer, Bagworm, Tent Caterpillar, and Leafminer spray

Bt (Bacillus thuringiensis ) – Thuricide, DiPel

Spinosad and Bt products are less likely to flare mites.

Treat small, recently planted trees with a hand sprayer or use a hose-end sprayer designed to treat trees and shrubs to treat trees up to 20 to 25 feet tall. Treat in mid-April through early June to control newly hatched caterpillars before they cause much damage. Adults are hard to control because they are protected by their bag.