Now that summer is here in Oklahoma, it’s time get ready to deal with that “infamous” insect pest known as the bagworm. Bagworms will eventually be out-and-about feeding on trees and shrubs, both broadleaf and evergreen, especially on juniper and arborvitae shrubs. So, how can you beat the bagworms this year? You can initially start by “hand-picking” any bags formed last year, before the overwintering eggs hatch, and place them into a container of soapy water or just destroy them. This is very therapeutic and, if feasible, will quickly remove large populations before they cause significant plant damage. For those less interested in the pleasures of “hand-picking,” there are a number of insecticides labeled or registered for the control/suppression of bagworm populations including Orthene, Tempo, Dylox, and others.
The key to managing bagworms with 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. 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. The active ingrediant must be consumed to be effective, so thorough coverage of all plant parts and frequent applications will be 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, which 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) works by contact and ingestion (stomach poison); however, it is most effective when ingested and it may be used against older or larger bagworm caterpillars. Bagworms can blow in from other areas, so multiple treatments may be needed.
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. Our Early Summer Tree & Shrub Treatment from LawnAmerica has an insecticide included which does a great job of bagworm control. We try to time this treatment to be applied just before the anticipated onset of bagworms, and other early summer insect pests.