Ask a Master Gardener
I’ve seen some bagworms on one of my evergreens. How do I get rid of them? AP
Some years, it seems like bagworms are everywhere. This year so far doesn’t seem too bad, that is unless you have bagworms on your shrubs.
While bagworms prefer arborvitae, eastern red cedar, and other junipers, they will also attach themselves to true cedars, pine, spruce, bald cypress, maple, boxelder, sycamore, willow, black locust, and oak. Some years we have even seen bagworms on the side of residences. Hopefully this will not be one of those years.
Bagworm eggs overwinter in those bags we are familiar with and emerge in late April or early May to begin to feed and to build their own bag. While many of the bagworm bags look familiar, they can vary in appearance depending on which host plant they are living on.
These bags start out about 1/4 of an inch in length but increase in size as the larvae grow to about 1.5 to 2 inches in length. These developing larvae move and eat by sticking their head out of the bag. Once mature, they permanently attach themselves to a branch of their host plant.
Once pupation is complete, the adult males emerge in late summer to early fall. These males are small, black, hairy moths with an extended wingspan of about 1 inch. Once they have emerged, they begin the search for females.
Female bagworms have a bit of a different trajectory. First of all, they are wingless, without functional legs, eyes, or antennae and spend their adult life inside of the bag.
When a male bagworm finds a bag containing a female, they enter the bag to mate. Once fertilized, the female can lay between 500 and 1000 eggs inside of her tiny home. These eggs overwinter inside the bag to emerge the following spring.
Control of these insects can be challenging since the bags protect them from any type of insecticide you might want to use. The easiest way to deal with bagworms in your landscape is to remove the bags by hand and dispose of them. Granted, this can be challenging in larger shrubs that are playing host to bagworms, but if you can, this is a sure-fire way to get rid of them.
We do have an organic pesticide called bacillus thuringiensis that works well on bagworms, but timing is critical. You must spray the plant in early June when you first start to notice the tiny bags. When the young bagworms eat greenery sprayed with bacillus thuringiensis, it will make them sick, and they will stop eating.
Spinosad is another organic pesticide that can work but again, you will need to spray when the larvae are feeding.
While timing is critical for pesticide application, the bags can be picked off the plant any time of year. Good luck.
You can 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 Street, or by emailing us at firstname.lastname@example.org. Photo: Mary C Legg, Bugwood.org