This is the time of year bagworms are munching away on landscape plants, and evidence of their destruction will soon appear. Bagworms can cause irreversible damage unless treated at the appropriate time. Consider this your yearly warning.
Bagworm feeding takes a toll on evergreens. Their favorites are junipers, spruce, and arborvitae. Because of the wide range of host materials, be sure to give all landscape plants a quick glance.
At first, they are hard to spot, but once too large to control, they are among the most easily identified insects. The young worm-like insects eat the foliage, resulting in an initial browning of the area, followed by the death of the plant under severe feeding. Understanding the bagworm’s life cycle helps you control its damaging effect.
Bagworms form a silken bag mixed with plant parts, eventually growing up to 3 inches in length. Bagworms spend most of their lives attached to a branch or stem, eating and never leaving the comfort of the bag. Only the males leave the bags to mate with the female, and then they die, and the female lays eggs for next year’s hatch.
Bagworms overwinter in the egg stage in bags attached to the plant. The eggs hatch in late May through mid-June. The hatchlings are tiny at first, starting about the size of a sharpened pencil tip.
They develop quickly, spinning a larger bag until mid- to late summer. At that point, the bagworms mate, eggs are laid, and the whole process is ready to start over for next year.
Populations build to damaging levels quickly as each bag of eggs produces more than 1,000 hungry tiny worms. They are best controlled while hatching in mid-June. Just about any insecticide will control bagworms while small, and the silken bag is not highly formed.
The larger the bag becomes, the less effective is the control. By late summer, chemical applications are useless. At this stage, handpicking and destroying the bags is recommended. This is a slow task most people would prefer not to do.
Small, developing bagworms treated now are easy to kill. Most insecticides are effective on bagworms at this time of year. Products to apply include Spinosad, Acephate, Cyfluthrin or Permethrin. An organic product called Bacillus thuringiensis is effective. Thorough coverage of the plant is vital for full control. Be sure to soak the developing bags with the spray.
Now is an excellent time to give your evergreen plants a close inspection for bagworms. Extension receives many calls each year from people attempting to identify this pest. They say something to the effect of “they just appeared overnight.” Although that is what it seems, they are indeed already present in your landscape.
Keep in mind they can do a lot of damage in a short time, so identifying bagworms early is essential to their control before it is too late, and you are left with an ugly plant.
Dennis Patton is a horticulture agent with Kansas State University Research and Extension. Have a question for him or other university extension experts? Email them to [email protected]