Bagworm is an insect that feeds on many coniferous and deciduous trees and shrubs. The most common of these are arborvitae, juniper, spruce and pine. This perennial pest forms a bag that hangs from the plant on which it is feeding. This bag is constructed with silk and pieces of leaves and twigs from the host. At maturity, this bag may be 30-50 mm in length. The larvae are splotched brown to black, but are seldom seen as they remain in the self-spun bag. Adult males have clear wings and bodies covered in fur. Adult females are worm-like, lacking eyes, wings, functional legs and mouthparts. She will never leave the protective bag she constructed while in the larval stage. This pest feeds on the needles and leaves of it's host. When searching for signs of bagworm in plant material, look for yellow spots on the foliage, usually in the upper portions of the tree, in late summer. Dead, open patches are common on coniferous hosts. 1-1/2 inch to 2 inch cone shaped bags can be seen hanging from tree branches by late summer. This pest can cause heavy defoliation by late summer. Most deciduous hosts can refoliate after defoliation. Damage from bagworm feeding tends to be much more destructive to evergreen plants. In many cases, these infestations aren't noticed until the damage is quite severe.
Bagworm can be challenging to control because they often go undetected until it is too late in the season to apply effective treatment. The larvae are much more sensitive to pesticide applications before they mature. It is important to time the treatments in early spring to mid-summer, depending on the size and species of host. Picking the bags off by hand before egg hatch can help to reduce populations, but is not always feasible. Look for bags during the winter to identify plants for treatment the following year. With proper timing and application, foliar spraying or soil injections of pesticides can provide good control of bagworm.
One of the most compelling features of the new home that we purchased in Buckingham in the summer of 2013 was it's lush, mature, and diverse landscaping. For the first several weeks after our move, however, we had little opportunity to enjoy it as we were inundated with moving boxes and the interior of our new home was in total disarray. I had noticed, nevertheless, that several of our large Colorado Blue Spruces were laden with many "pinecones”; imagine our surprise when, one day, my husband saw them in motion. Upon closer inspection, we recognized that these beautiful trees had an infestation of bagworms. Read more>>