Bagworms: How and When to Treat

Jun 21, 2024

Well, the weather is getting consistently warmer, the first of our warm weather crops are going in, and all is right in the gardening world. Except you look at your juniper and notice the slightest movement. Upon investigation, you see a tiny worm in a teardrop shaped bag nestled in the branches. That’s right, the bagworms have come again…

When to Start Looking

Bagworms can hatch in Missouri as early as the end of April, to the beginning of May. Although very tiny at this point, they can start wreaking havoc on many evergreens quickly, and can be of a noticeable size by the 3rd week of May. I recommend checking plants that have had them in the past years in the 2nd week of May and continuing to check every few days until you spot them.

What to Look For

Most people have seen bagworms before, even if they’re not sure what they’re looking at. Most plants that tend to get bagworms are evergreens like juniper, arborvitae, spruce, and cedars. I’ve seen them on occasion on burning bush, crabapple, and honey locust. Look for small, teardrop shaped bags between ½’’ (Juvenile) to 2’’ (Adult). They can be hard to spot, as they make their “bag” out of the trees foliage that they are feeding on. Looking for light movement on the tree, typically in early morning

What to Do

When you do spot this pesky critter, I recommend spraying the tree with an insecticide. While there are many treatment options, I tend to use the following:

  • BT- Bacillus thuringiensis is a biological option that is very effective against all non-beneficial worms. It can be used for army worms, tent caterpillars, cabbage loopers, and of course, bagworms.
  • Captain Jack’s Dead Bug Brew- with an active ingredient of Spinosad, another biological option that is effective against many types of non-beneficial worms, as well as some other garden insects like thrips, mosquitos, spider mites and some types of beetles.
  • Bonide 8 Garden and Home- this broad-spectrum insecticide is useful for controlling many types of insects on ornamental and edible plants alike, including Japanese beetles and bagworms.

When applying the insecticide, total coverage of the plant is needed. Spray the interior of the plant, the undersides of the plant and the exterior until the plant is dripping. I recommend using the Rule of 7, which is spraying before 7am or after 7pm. This limits the number of beneficial insects that are active, as well as the product being able to be effective in treating the insect.


Written By "Trav the Tree Guy" Morcha, Nurseryman