If you haven’t scouted for bagworms yet, trust me — they are out and about. They are a recurring pest in our area and can cause significant damage to landscape plants. Unfortunately, many homeowners do not become concerned about bagworms until they notice the large bags hanging from trees and shrubs. By that point, the damage has often already been done. Fortunately, the ideal window for control is approaching.
Bagworms overwinter as eggs inside the protective bags left by female moths. From mid-May through mid-June, larvae hatch and emerge through the bottom opening of the old bag. They immediately begin constructing their own miniature silk-lined bags, incorporating bits of foliage into the structure for camouflage. Once the bags are completed, the young larvae begin feeding. As the larvae grow, their bags expand.
By mid- to late August, feeding is complete. The mature larvae firmly attach their bags to twigs and branches, where they remain protected as they complete their life cycle.
BAGWORMS are most commonly found on eastern redcedar and juniper, but they also attack arborvitae, spruce, and pine. In addition, many broadleaf trees, shrubs, and ornamental plants can serve as hosts. After defoliating a plant, bagworms may migrate in search of additional food sources, attacking either the same species or entirely different plants.
The extent of damage can range from minor to severe. As larvae grow larger, their appetite increases dramatically. In some cases, what appears to be a healthy tree can become heavily defoliated in a very short period of time. Several consecutive years of severe feeding can weaken and eventually kill trees, especially conifers.
There are two primary methods of bagworm control: cultural and chemical.
For those who prefer not to use insecticides, handpicking bags from infested plants can be an effective management strategy. This is often easiest during the winter months when the bags are more visible against dormant foliage and branches. However, it is important to remember that a single overlooked bag may contain hundreds to more than a thousand eggs. Handpicking also becomes impractical when plants are heavily infested or too large to reach safely.
CHEMICAL control is most effective when larvae are young and actively feeding. In most years, bagworm larvae begin emerging from overwintering bags in mid- to late May. Because egg hatch occurs over 4 to 5 weeks, treatment timing is important. Insecticide applications made in late summer are often ineffective because the larvae are larger, more resistant, and may have already stopped feeding.
The third week of June is generally the ideal time to apply insecticides for bagworm control. Products containing spinosad, acephate, cyfluthrin, or permethrin are commonly used and are available under a variety of trade names. Always read and follow label directions, and check the active ingredients to ensure the product is labeled for bagworm control.
For more information on managing bagworms, get in touch with me at your local K-State Extension, Southwind District office in Iola, Erie, Fort Scott, and Yates Center.
Krista Harding is a K-State Research and Extension Horticulture agent assigned to the Southwind District. She may be reached at [email protected] or 620-244-3826.
