KC Gardens

Bagworm hatchlings could be feeding on your plants. Here’s how to control the pests

Bagworms on an arborvitea. For larger bags, handpicking them off the plant is the best method of removal.
Bagworms on an arborvitea. For larger bags, handpicking them off the plant is the best method of removal. Johnson County K-State Research & Extension

It is one of the most easily identified insects found in our area — the bagworm.

Bagworms are now munching their way through many landscape plants, and their favorites tend to be evergreens such as junipers, spruce and arborvitae.

Because of the wide range of host material, 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. Under severe feeding, the plant will die.

Understanding the bagworms’ life cycle will help you control their damaging effect.

Bagworms form a silken bag, mixed with plant parts, up to 3 inches long. 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 over-winter 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, about the size of a sharpened pencil tip.

They develop quickly, spinning a larger bag until mid to late summer. The bag is thick and about 2 to 3 inches in length. At that point the bagworms mate, eggs are laid, and the whole process starts over for next year.

Bagworm populations build up to damaging levels very quickly as each bag of eggs can produce more than 1,000 hungry little worms.

Control bagworms after they hatch in the early summer. Just about any insecticide will kill the worms while they are small and the silken bag 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 is recommended. This is a slow task that most people would prefer not to do.

There are many insecticides that 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.

Now is an excellent time to give your evergreen plants a close inspection for bagworms. I receive a number of calls each year from people attempting to identify this pest. They say something to the effect of, “they just appeared overnight.”

But there are clues to their arrival. They can do a lot of damage in a short time, so identifying bagworms early is essential to their control.

Dennis Patton is a horticulture agent with Kansas State University Research and Extension. Got a question for him or other university extension experts? Email them to garden.help@jocogov.org.

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