Landscape Pests

Winter 2008                                                                Print this page (PDF)

BAGWORMS ON LANDSCAPE PLANTS
Tree and Shrub Infestations

Control Tips

Manual control

Bagworm infestations on smaller trees and shrubs can be controlled by removing bags before the eggs begin to hatch. Destroy the bags by crushing them between gloved fingers or by immersing in soapy water or by burning in a controlled way - say a small coffee can or other container. If the bags containing larvae are simply discarded on the ground, the larvae may return to your tree or any nearby plant

Chemical controls are effective if applied during the early stages of development. For most effective insecticidal control and prevention of damage to trees and shrubs, apply sprays from early to mid-June. Because of the 3 or 4 week hatching period, two spray applications, two weeks apart, may be warranted for maximum control of heavy infestations

Over 128 plant species have been reported as host plants for bagworm, though arborvitae, red cedar and other juniper species are most commonly attacked.

Chemical control becomes less effective as the season progresses because of the increased size of the larva and its bag. Insecticides that can be used against the bagworm include BT (Bacillus thuringiensis), Sevin, permethrin and other pyrethroids, Orthene, or malathion. Apply according to label directions.

Bagworms are caterpillars that build distinctive spindle-shaped bags on a variety of trees and shrubs throughout  the Midwest. They attack both deciduous trees and evergreens, but are especially damaging to juniper, arborvitae, spruce, pine and cedar. Large populations of bagworms can strip plants of their foliage and eventually cause them to die. Infestations often go unnoticed because people mistake the protective bags for pine cones or other plant structures.

Bagworms pass the winter as eggs inside the bag that contained the previous year’s female. In mid to late May the eggs hatch, and the tiny larvae crawl out from the end of the bag in search of food.

Close up view of pest

Control can be achieved on small shrubs and trees by handpicking or cutting the bags from infected plants in late fall, winter, or early spring, disposing of the bags to prevent re-infestation.

Bagworm larvae

A mature bagworm emerges to feed
 

Using silk and bits of plant material, the newly hatched larvae soon construct a small bag around their hind part that looks like a tiny, upright ice cream cone. As the larvae continue to feed and grow, they enlarge the bag enabling them to withdraw into it when disturbed. Older larvae strip evergreens of their needles and consume whole leaves of susceptible deciduous species, leaving only the larger veins.

The bag is ornamented with bits of whatever type of vegetation they are feeding upon. This technique makes them hard to detect until they have not only gotten larger, but have already managed to damage their host by eating large amount of foliage, even to the point of stripping off significant portions of foliage on a tree or shrub.

Bagworms may come into the landscape from infected nursery stock or  may be carried in by wind after hatching. They often become apparent only after significant feeding has occurred, so every effort should be made to remove visible infestations before further hatching occurs, in late winter or in early spring. 

Find bagworm infestations by making a quick visual inspection of any newly installed trees, evergreen shrubs or plants displaying signs of stress. Pick a sunny, late-winter day when the temperatures are above freezing, but not yet warming towards 50 degrees F and carefully inspect landscape material for this easy to control, but prolific pest.  Without leaves in the way, they are relatively easy to see, even from a distance.

Arborvitae are often hosts to bagworms

A mature male bagworm