Thursday, June 25, 2015

How to Deal with Bagworms

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.

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). 

Adult bagworms in a tree (Photo courtesy of Jim Kalisch, UNL Entomology)