There has been word that bagworms, Thyridopteryx ephemeraeformis, are emerging from eggs, and the young caterpillars are already out and about feeding on plants. Eventually bagworms will be present throughout our region feeding on both broadleaf and evergreen trees and shrubs. So, now is the time to take action against this insect pest.
Bagworms are primarily a pest of conifers but have expanded their host range to include a number of broadleaf plants, such as rose, honeylocust, and flowering plum, to name a few. Hand-picking small caterpillars (along with their accompanying bag) and placing them into a container of soapy water will kill them directly. This practice, if feasible, will quickly remove populations before they can cause substantial plant damage.
Not into hand-picking bag-worms? There are a number of insecticides that can be used to control bagworms, including those with the following active ingredients (trade name in parentheses): acephate (Orthene), Bacillus thuringiensis subsp. kurstaki (Dipel), cyfluthrin (Tempo), lambda-cyhalothrin (Scimitar), trichlorfon (Dylox), indoxacarb (Provaunt), chlorantraniliprole (Acelepryn), and spinosad (Conserve). Most of these active ingredients are commercially available and sold under various trade names or as generic products. Several insecticides, however, may not be directly available to homeowners.
The key to managing bagworms with insecticides is to apply early and frequently enough to kill the highly susceptible young caterpillars that are feeding aggressively on plant foliage. Older caterpillars that develop later in the season are usually more difficult to kill with insecticides. Furthermore, females feed less as they prepare for reproduction, which reduces their susceptibility to spray applications and any residues.
The bacterium Bacillus thuringiensis subsp. kurstaki is active on young caterpillars but the active ingredient must be ingested to be effective. Therefore, thorough coverage of all plant parts and frequent applications are required. Spinosad is the active ingredient in a number of homeowner products, including: Captain Jack’s DeadBug Brew, and Monterey Garden Insect Spray. The insecticide works by contact and ingestion (stomach poison); however, activity is greatest when ingested. Products containing spinosad can be used against older or larger bagworm caterpillars later on in the season. Acephate (Bonide Systemic Insect Control), cyfluthrin (Bayer Vegetable & Garden Insect Spray), gamma-cyhalothrin (Spectracide Triazicide), trichlorfon, chlorantraniliprole, and indoxacarb can be used against both the young and the older caterpillars.
Thorough spray coverage of all plant parts, including tree tops and surrounding shrubs, in multiple applications, is essential in keeping bagworm populations at bay. The reason multiple applications are recommended is that bagworm eggs do not hatch simultaneously but hatch over a period of time depending on temperature. Also, young bagworms can “blow in” (called “ballooning”) from neighboring plants on silken threads.
If left unchecked, bagworms can cause a lot of damage, ruining the aesthetic quality of plants. Moreover, bagworms can actually kill plants, especially small evergreens that may be newly transplanted, because evergreens do not usually produce more than one flush of growth per growing season.

Rip Winkel is the horticulture agent in the Cottonwood District for K-State Research and Extension. Contact him by email at rwinkel@ksu.edu or call either 785-682-9430, or 620-793-1910.