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The bagworm is a caterpillar that builds a bag out of plant material. The female lives her entire life in the bag, producing up to 1,000 eggs and dying. The eggs overwinter in the bag and hatch in spring. Destruction begins as the larvae leave the bag, construct their own bags and begin feeding on the arborvitae's foliage. A heavy infestation of bagworms can completely defoliate an arborvitae and kill it.
Pick the bags off the arborvitae and burn them. You can also drop them into a bucket containing a gallon of water and 2 tbsp. of liquid soap.
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Apply an insecticide containing neem, pyrethrin, esfenvalerate or acephate, all of which are effective against this pest. A biological spray containing Bacillus thuringiensis (Bt.) will also work. Spray the arborvitae with a garden sprayer and insecticide from May to June at the interval suggested on the label.
Repeat the insecticide application at the end of June to kill any bagworms that hatched after the initial application.
Insecticides and garden sprayers are available at garden supply or home improvement centers.
- "Texas A&M AgriLife Extension"; Bagworms; B.M. Drees, et al.; 1999
- "Southside Sentinel"; Time to Battle Bagworms; David Moore, et al.; April 2009
- "Iowa State University Extension:; Bagworms--A Review and a Prediction; Donald Lewis; February 2009
- "University of Illinois Extension"; Plan Now to Control Bagworms; Sandra Mason; May 2006