Bag worms

Typically, bagworms cause minimal damage to host plants. Bill Sevier/for the Tulsa World

I have bagworms all over my arborvitae. What can I do to get rid of them? JG

Bagworms seem to be everywhere this year. Getting rid of them can be a challenge, but it’s possible if you are up to the task. First, let’s talk about the bagworm life cycle because understanding their life cycle is key to controlling them.

To begin, lets go back a couple of months. Bagworm larvae overwinter in the bag and begin to emerge in late April or early May. Once emerged, these larvae begin to feed and construct the bags with which we are familiar. Initially, these bags may be only ¼ of an inch in length. But, as the larvae feed and begin to grow, they increase the size of the bag. This feeding is what can cause damage to the host plant. You mentioned arborvitae, but they also like eastern red cedars and junipers. However, in peak seasons, they can make their homes on pines, spruce, bald cypress and others.

For the female bagworms, the bag is their forever home. They do not develop wings, legs, eyes or antennae and are almost maggot-like in appearance. Adult females can grow to about 1 inch in length. Males on the other hand grow to become small black moths that have a wingspan of about 1 inch.

Pupation occurs within the bag, and in the late summer or early fall, the males emerge from their bags in search of females. Adult males and females have a short lifespan — the female, a couple of weeks; the male, only a couple of days so the search is on. Neither the adult female nor male feeds. After mating, the adult female lays several hundred eggs within her bag and then dies. The eggs overwinter within the bag only to start the cycle all over again the following year.

So back to your question of what to do about them. With bagworms, timing is everything. When they are in their bags, about the only thing you can do is to remove them by hand, and you can do this any time of year. If your shrub is of an appropriate size, this is a good strategy, one the kids might enjoy helping with as well. Once the bags are collected, they need to be destroyed or placed in a sealed bag in the trash.

About the only other time you have a shot at control is in April and May when the larvae are feeding. During this time, you can spray with an organic pesticide called Bacillus Thuringiensis or Bt for short. This organic pesticide only affects feeding caterpillars. You spray the pesticide on the infested plant, they ingest the pesticide while eating and die. Spraying this time of year while the bagworms are in their bags will not be an effective strategy as the bag does a great job of protecting them from harm.

Typically, damage is minimal from bagworms. However, infestations that build up over time can be detrimental to the health of your plant. So taking appropriate action at the appropriate time is key to bagworm control.

Get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th St., or by emailing mg@tulsamastergardeners.org.


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