Now Is Time to “Nail” Those Bagworms

It is now time to “do battle” (I love military metaphors) with that “infamous” of insect pests known as the bagworm (Thyridopteryx ephemeraeformis). Throughout most of Kansas, bagworm eggs have hatched and the young caterpillars are out-and-about feeding on both broadleaf and evergreen trees and shrubs. Bagworms were first considered a pest of primarily conifers but over the years they have expanded their host range to include a number of broadleaf plants including rose, honeylocust, and flowering plum. I have even seen them “eating chicken wire” at the Sunset Zoo (Manhattan, KS). At this time of year, what is the best way to deal with bagworm caterpillars and thus prevent them from causing damage? Handpicking any small caterpillars (along with their accompanying bag) and placing them into a container of soapy water will kill them directly. This is highly therapeutic and, if feasible, will quickly remove populations before they can cause substantial plant damage. You should consider having a weekend “bagworm handpicking party” with prizes awarded to those individuals that collect the most bags.

For those less interested in the pleasures of handpicking, there are a number of insecticides labeled for use against bagworms including those with the following active ingredients (trade name in parentheses): acephate (Orthene), Bacillus thuringiensis subsp. kurstaki (Dipel/Thuricide), cyfluthrin (Tempo), lambda-cyhalothrin (Scimitar), trichlorfon (Dylox), indoxacarb (Provaunt), chlorantraniliprole (Acelepryn), and spinosad (Conserve). Many of these active ingredients are commercially available and sold under different trade names or generic products. However, several insecticides may not be directly available to homeowners. The key to dealing with bagworms when using insecticides is to make applications early and frequently enough in order to kill the highly susceptible young caterpillars that are feeding aggressively on plant foliage. Older caterpillars that develop later in the season, in the bags, may be 3/4-inches long, and are typically more difficult to kill with insecticides. In addition, females tend to 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; however, the active ingredient must be consumed to be effective, so thorough coverage of all plant parts and frequent applications are required to avoid having to deal with later stages. This compound is sensitive to ultra-violet light degradation and rainfall, which reduces any residual activity. Spinosad is the active ingredient in a number of homeowner products (including Borer, Bagworm, Tent Caterpillar & Leafminer Spray; Captain Jack’s DeadBug Brew; and Monterey Garden Insect Spray) and works by contact and ingestion (stomach poison); however, it is most effective when ingested and it can be used against older or larger bagworm caterpillars. Cyfluthrin, lambda-cyhalothrin, trichlorfon, chlorantraniliprole, and indoxacarb may be used against both the young and the older caterpillars. However, thorough coverage of all plant parts, especially the tops of trees and shrubs, where bagworms commonly start feeding, and frequent applications are required. The reason why multiple applications will be needed when bagworms are first detected is because bagworms “blow in” (called ‘ballooning’) from neighboring plants. If left unchecked, bagworms can cause significant damage, thus ruining the aesthetic quality of plants. In addition, they may actually kill plants, especially evergreens since they don’t usually produce another flush of growth, and newly transplanted small plants. If you have any questions regarding the management of bagworms, contact Reno county horticultural agent, Pam Paulsen at 620- 662-2371 Contributors: Ray Cloyd, Entomologist/Ward Upham, Extension Associate