They’re small but mighty, so attack bagworms now before they damage evergreens
They’re quietly munching away and at first can be hard to spot.
But once the bagworm population is too large to control, they are among the most easily identified insects. Bagworms have made their annual appearance and their feeding is taking a toll on evergreens.
Bagworms feed on many different plant materials, but their favorite are junipers, spruce and arborvitae. Because of the wide range of host material, be sure to give all landscape plants a quick glance to assess for damage.
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 will help you control their damaging effect.
Bagworms form a silken bag mixed with plant parts, eventually growing up to three 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, 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 can produce more than 1,000 hungry little worms. They are best controlled after they hatch in the early summer. Just about any insecticide will kill the worms while they are small and the silken bag is not highly formed.
The larger the bag becomes, the less effective the control. By late summer, chemical applications are worthless. At this stage, handpicking and destruction of the bags are recommended. This is a slow, nasty task and one I would prefer to skip.
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 also 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.”
Even though they seem to appear almost overnight, there are clues to their arrival. 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.
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 garden.help@jocogov.org.