Bagworms tend to be a problem on trees that are isolated or in urban settings. When bags are found in the tree, simply pick the bagworms off and drown them in a bucket of soapy water. This method is most effective before eggs hatch out of the bags in June.
Bagworms can be controlled by spraying the foliage with insecticides after eggs have hatched and small bags are seen on the trees. Caterpillars must consume the foliage for the insecticide to kill them. For best results, use a biorational pesticide listed in Table 1. The biorational materials will only kill caterpillars without killing the natural enemies of spider mites and scale insects that can cause additional damage to the plant. (See E-42-W Spider Mites on Ornamentals
and E-29-W Scale Insects on Shade Trees and Shrubs
). Caterpillars may have to feed on treated leaves for 1-2 days to get a lethal dose of these materials. In contrast, rescue materials can kill caterpillars feeding on the foliage within hours after application. All pesticides are most effective when directed against worms in bags that are still small. Dipel is only effective on bags < 1" long. Two weeks after any pesticide application, look for live bagworms to determine if additiona treatment is needed.
Alternatively, a soil application of dinotefuran may be applied to the base of the tree. Applications should be made in early May to allow enough time for this material to get into the foliage before eggs hatch. Our research has shown this product to be most effective on young bagworms. A homeowner product will be available for use in 2010.