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Beating Back Bagworms

By Paul James

Bagworms can be a bummer. Left undetected and uncontrolled, they can quickly defoliate and destroy their host plant, particularly conifers — junipers, pines, spruces, bald cypresses, and the like — and to a lesser degree maples, sycamores, willows, oaks, even roses. And now’s the time to be on the lookout for them.

So what exactly are you looking for? Last year’s “bags” or cocoons, for starters. Bagworms overwinter in their carefully constructed homes, so now’s a good time to inspect plants and remove any leftover bags, because the eggs within them (which can number in the thousands) will soon be hatching and developing into larvae (tiny caterpillars). The larvae then release a thin silk thread and float down out of the bag or are carried by the wind to other plants to begin feeding and creating new bags made of leaves and twigs, all bound together with silk.

The larvae themselves are tiny and hard to see, so look instead for the tiny bags as they begin to form and begin treatment right away.

Two of the best controls — other than handpicking — also happen to be all natural and approved for use by organic gardeners — Bt (Bacillus thuringiensis) and Spinosad. Bt is available as a dust or liquid and should be applied in the early evening or on a cloudy day because it breaks down quickly when exposed to sunlight. Spinosad (such as Captain Jack’s Dead Bug Brew) is also available as a dust or spray.

It may take two or three repeated treatments spaced a week apart to achieve complete control, and both Bt and Spinosad should be reapplied after heavy rains.

So what happens if you don’t get rid of bagworms in spring? Well, their life cycle begins anew in September. Male bagworms — fuzzy black moths with transparent wings that live only one or two days as adults — emerge from their bags in search of a mate, and with no time to spare. Female bagworms — who have no functional eyes, legs, mouthparts, or antennae — spend their entire lives in their bags and ultimately decay into a mass of eggs. Come spring, the eggs hatch into larvae in search of your plants.

Happy gardening, ya’ll.

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9 responses to “Beating Back Bagworms”

  1. Greg says:

    Hi Paul, i am glad you brought this topic up, because I am in the thick of this now. I have a juniper with not only a massive bagworm “infestation,” but its sitting next to a couple of beautiful old apple trees…So, I have a double whammy…1. The worms, and 2. cedar apple rust. The rust has impacted the apples the last couple of years. I am thinking I have to call it quits and take down the juniper to salvage any apples this year. Am I too late? I’m in NJ, and I think I’m zone 6b?

    • Paul James says:

      It’s too late to do much about the fungus now, but you can spray a copper-based fungicide as a preventive next year. You can certainly remove the juniper, but if there are any in your neighborhood within a quarter mile or so your apples will still get infected. Good to hear from someone in the Garden State. My oldest son went to Princeton so we’ve spent a lot of time there. Thanks for writing, Greg. Be safe.

  2. dEDE says:

    THANKS Paul – had a serious case of bagworms on my Buckthorns last year, spent hours pulling of HUNDREDS of them but eventually got ahead of them and saved my plants…. they do spread to other plants in the area – really have to keep an eye out for them as they will really eat all the vegetation off a plant in a very short time! Have my Captain Jack’s ready if they come back this year! Love to read all of your helpful posts!

    • Paul James says:

      Sorry about your Buckthorns. That’s a plant I really love. Thanks for reading.

      • Dede says:

        YOU are the reason I bought the Buckthorns – you showed them in one of your classes! They are doing great now – no bagworms!!! I enjoy your classes as I have learned about new plants to try! Distylium, Fine Line Spirea are two more of my favorites! THANKS for all the information you share!

  3. Brandon says:

    Thanks, Paul. I have found these bagworms actually make great bait for fishing! In Tennessee, large mouth bass love them. Miss your show! I keep watching the reruns on HGTV. I keep hoping to one day see you return. You taught me everything I know about gardening. Don’t forget you still have a very loyal following out there.

    God Bless,

    • Paul James says:

      Thanks, Brandon. I never thought of using bagworms as bait, but I’ll give them a try. I appreciate the kind words. Keep on gardening!

  4. Jean Genske says:

    We have an oak tree whose leaves are small and already turning brown and falling off. It is becoming very bare. Jean The bark is splitting and peeling away from the tree. We just noticed some bag worms hanging from the tree and didn’t know what they were till I saw your blog. At this point, is the tree beyond saving?