The Homeowners Column

The Homeowners Column

Controlling Bagworms

Photo of Sandra Mason

Sandra Mason
Extension Educator, Horticulture
slmason@illinois.edu

When I was a kid, I quickly learned the perils of lamenting about my boredom. Whining yielded an assignment to the bagworm picking squad on the backyard junipers. I was seldom that bored.

Bagworms hang like Christmas ornaments from evergreens such as arborvitae, red cedar, but also deciduous trees such as maples and crabapples. Severe damage may occur on evergreens since leaf loss can cause branch death.

The adult bagworms are interesting looking moths. The female won't be the first moth asked to dance at the next porch light dance. She is eyeless without wings, legs or antennae or functional mouthparts. She has a soft yellowish white, almost hairless body and never leaves the bag. (Do you blame her?) The male moths are black and almost clear winged. The male moth emerges from his bag, flies to the female, mates and dies in a few days. I guess he doesn't have a great life either, but at least he gets to leave the house.

The female produces 300-1,000 eggs in the bag, which can mean large populations on a single plant. They spend the winter as eggs in the bag.
The bag is made of silk and bits of twigs and leaves of the host plant. Active bags will have green leaves on the top. The bag enlarges as the caterpillar grows and everywhere the caterpillar goes the bag is sure to follow.

In central Illinois bagworm egg hatch should occur in mid June, even this year. Control should begin in early July to allow full caterpillar emergence.
The newly hatched tiny caterpillars move around by "ballooning." The young caterpillars climb high into trees. They produce a 2-3 foot long silk streamer that acts as a balloon to keep them drifting on the wind. Eventually they hit the side of a building or your favorite juniper. Feeding usually starts at the top of the plant.

The caterpillars and bags are quite small at first and may go unnoticed except for brown leaves. Once bags reach 3/4 of an inch, they are difficult to control with insecticides.

The insecticide Bacillus thuringiensis kurstaki sold as Dipel, Thuricide or Caterpillar Attack are effective against the young larvae. Bt products are nontoxic to humans, wildlife, beneficial insects and other organisms not closely related to the pest. Bt has to be eaten to be effective. Once caterpillars are large and stop feeding, insecticides are useless. Handpicking of the bags is the only control from fall through midspring so find a really bored child.

U of I Extension Master Gardeners Garden Walk Sunday June 17 from 10-5. Tickets are $8 in advance and $10 on the day of the walk at the Idea Garden. Available in Champaign at the University of Illinois Extension office at 801 North Country Fair Drive (217) 333-7672, Abbott's Florist, Greenview Nurseries, Jack's Greenery, Rick Orr Florist and Prairie Gardens. In Urbana purchase tickets at Country Arbors Nursery, FS Farmtown, and English Hedgerow and each Saturday at the Urbana Farmers' Market. Tickets are also available at Mourning Dove Farms in Mahomet, Pages for All Ages Bookstore in Savoy, Kleiss Nursery in Tolono, Pine Acres Herbs in Sidney and in St. Joseph Hidden Acres and Calico Heart.

All Garden Walk proceeds go toward Master Gardener projects in Champaign County such as our stupendous Idea Garden.

Other area garden walks:

  • Monticello Garden tour Saturday, June 16 from 10-4. PH: 800-952-3396.
  • Mahomet Garden Walk on Sunday, June 24 from 11 am to 5pm. Tickets and maps are available at Mourning Dove Farms.
  • U of I Extension Vermilion County Master Gardeners Garden Walk Sunday, June 24 from 12-5 in Danville. Contact U of I Extension Vermilion County (217) 442-8615.

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