Bagworms are a very well-known pest in Kansas and June is the time to begin inspecting for and planning to control any infestations. They are commonly found feeding on junipers and other evergreen trees and shrubs, but aren’t limited to evergreens. Many deciduous trees and shrubs also serve as suitable hosts to bagworms.
Bagworms can cause extensive damage to evergreen plants. Junipers though tough, can be weakened or even killed by a severe attack. Evergreen plants do not have auxiliary buds from which they can regrow quickly after bagworm feeding. Once the foliage is lost, it may be too late.
Deciduous trees and shrubs on the other hand are rarely affected long term by bagworm feeding since they can readily sprout new growth from dormant auxiliary buds.
Timing is critical
Treatment of bagworms depends on good timing. Bagworms begin hatching in late May through early June. Their feeding is easy to miss early in the summer since they are quite small and do relatively little damage early on. In many cases by the time heavy damage is noticed the bags are quite large and control becomes much more difficult if not impossible. Bagworms quit feeding in mid to late August and tie off their bags. Treatment after the bags are tied off has no effect since they are protected by the thick bag.
The best time to scout and treat for bagworms is from mid-June to early July. This is the time period where bagworms are very actively feeding, but still small and easier to control.
Take time to closely inspect trees and shrubs for bagworm presence now. Lush growth can make it difficult to find the small but growing bags. Once a small bagworm is discovered others will quickly be recognized if they are present, and will be seen moving and feeding.
Treat if necessary
There are many active ingredients that will be quite effective at killing bagworms. Look for an insecticide that has bagworms listed on the label and follow the directions on the label closely-including wearing the proper protective clothing/gear when making an application.
The two most important factors for bagworm control are proper spray timing and thorough coverage of the trees or shrubs with the chosen insecticide.
For trees that haven’t been heavily damaged by bagworms in the past, one thorough insecticide spray in late June or early July should be all that is needed to avoid damage. For trees that have been damaged heavily in the past by bagworms two sprays are often recommended. The first in early to mid-June to control the initial hatch and the second 3-4 weeks later to eliminate the latter hatching bagworms.
Remember that just spraying the outside branches of a tree or shrub will not solve the problem. Many bagworms live in the interior and can easily move to the exterior to feed if not killed by the spray. Be sure to thoroughly treat infested trees inside and out.