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Rhonda Ferree's ILRiverHort

Rhonda Ferree's Horticulture Blog
Bagworm on spruce
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Control Bagworms Now!

Bagworms have hatched throughout Illinois! This is the best time to control them, so act now! If you have seen bagworms on any of your plants in the past, check them now for activity. Most people call me about bagworms in the fall when they are too large to easily control.

There are several different insects that people call bagworms, including the tent caterpillars and webworms. The bagworm I am referring to is smaller and builds individual diamond shaped bags that hang all over the plants.

Bagworms attack a wide range of evergreen and deciduous trees and shrubs (128 plant species). According to University of Illinois Extension Entomologist Dr. Phil Nixon, they are most common on spruce, eastern red cedar, other junipers, arborvitae, white pine, crabapple, and pin oak.

Most bagworms are actively feeding right now. Small grayish, black colored worms just emerged from last year's bags. They are so small that you will not notice them without careful inspection, but they have begun to feed upon whatever leaf material is present. Unfortunately, they are usually not noticed until significant damage is done. Because young larvae migrate to the tops of trees and shrubs, look in these areas for early infestations.

Do not wait to treat. You can manually pick the small bags off and kill them, but they are hard to find at this stage. Fortunately, the small caterpillars are very susceptible to insecticide treatment right now. In central Illinois, the larvae will have finished their ballooning by now so a single application of Bacillus thuringiensis kurstaki-BT (Dipel, Thuricide), spinosad (Conserve), cyfluthrin (Tempo), permethrin (Astro), and other pyrethroids are effective even on older larvae.

I recommend using the biological insecticide B.t. kurstaki (Dipel, Thuricide) as it affects only caterpillars of moths and caterpillars. Do not wait, as the insecticide is less effective once the bags are larger and the caterpillar has pupated. As always, be careful when using any pesticide and read label directions carefully.

In a few weeks the caterpillar will change from a larval (caterpillar) stage to a resting (pupa) stage. Later this year they will emerge from the pupa within the bag as either wingless, nearly legless females or furry, black, winged males. The females remain in the bag, but the males leave it behind in search of females to mate with. Females lay nearly 500 eggs per bag and then die. The bag serves as over wintering protection for the eggs that will hatch next June in central Illinois.

For more information on bagworms and other current pests (including Japanese beetle), go to my blog at I also post current information on my Facebook Page at

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