Bagworms are some of the best architects in the insect
world. These caterpillars take materials from the plants they live in and
construct a tough bag to dwell in as they grow. The bag grows in size as they
do and protects them from the elements and predators. Bagworm caterpillars have
voracious appetites and can drastically damage evergreens like pine, spruce,
juniper, arborvitae, and cedar and will occasionally feed on deciduous trees.
Luckily we have several tools at our disposal to eliminate these hungry, hungry
caterpillars.
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| Young bagworms just getting started in a tree (Photo courtesy of Jim Kalisch, UNL Entomology) |
For the best control you need to understand this pest’s unique
life cycle.
- In the early summer (May-June) bagworm eggs will hatch and the
small caterpillar will build their home. You may notice small triangular shaped
objects moving in your bush or shrub. Some will stick around the plant they
hatched in but other will perform a behavior called “ballooning”. This is where
the caterpillar releases a line of silk and the wind carries them, sometimes
for miles, to a new plant to infest.
- The caterpillars will feed for approximately six weeks in order to
finish development. They will pupate inside of their bag and then the males
emerge as dark, fuzzy moths. The females don’t grow wings or ever leave the
bag; they become sort of a super caterpillar and produce a pheromone to attract
males to their bag.
- After mating the female will lay her eggs inside of her bag so
they can hide over the winter. She will perish but there will be 200-300 of her
eggs safe to hatch the next spring.
You have a few organic options to control bagworms. You can practice mechanical control, where you would go out in the
late fall or early spring and cut bags from trees. This will remove any eggs
that may hatch in your tree but won’t protect you from new caterpillars blowing in. You
can also keep a close eye on your evergreens and when you start to see the
small bags pop up spray a product containing Bt (Bacillus thuringiensis) to control the young
caterpillars. Other options at this time would be products with spinosad or
azadirectin.
If you miss your chance to do these early stage controls you can
control larger bagworms with synthetic products like Sevin (carbaryl), Ortho Tree &
Shrub (or other bifenthrin containing products), or Bayer Tree and Shrub (or
other products containing cyfluthrin).
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| Adult bagworms in a tree (Photo courtesy of Jim Kalisch, UNL Entomology) |
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