How to Deal with Bagworms

bagworm moth by teejaybee

It is mid July in steamy Charleston, SC and I have just discovered I have bagworms on 2 of my 45′ Leland cypress trees. I am not getting call backs from people who could treat this. Maybe it is too late in the year and they know it is hopeless. I am too old to be out in the 104 heat index to hand pick the cone sacks and I can’t get up high enough anyway. The worms are spreading to roses and other shrubs. What should I do?

I am sure that you are correctly identifying bagworms. Because by the time you are seeing them, they are happily living in their bags and are quite obvious. And when they are dangling like ornaments on the trees, other than hand picking the cocoons, they are difficult to kill by using any insecticide that will effectively kill them.  Insecticides are most effective when applied during the early stages of bagworm development which is in the early spring.

Bagworms feed on most coniferous plants and on many deciduous trees and shrubs and can be a  problem to over 100 different plants. If the infestation is heavy, it can kill the plant.

Bag Worm Cocoon by Justin_D_Miller

Though there are not many things that one can do to try to prevent bagworms, there is some evidence that planting plants in the aster family in your yard might attract a beneficial wasp that will kill bagworms. (see here)

Since you live in South Carolina, your state agricultural extension office is Clemson University. They have a fact sheet that discusses the problems of bagworms on the Leyland Cypress and how to handle the problem.

Here is what The Clemson Extension Fact Sheet recommends:

“Prevention & Control: Several parasites and predators feed on bagworms, generally keeping their numbers under control so that damage is not noticed. Removal of the egg-containing bags during winter and early spring is a very effective method for preventing problems before the next growing season. Once removed, the bags should be destroyed or placed in a deep container (5-gallon bucket), which allows beneficial parasites that may also be present in the bags to escape while retaining the bagworm larvae.

If an infestation is severe or the bags are out of reach, spray with the bacterial insecticide, B.t. This insecticide contains spores of the bacterium, Bacillus thuringiensis, which when eaten, kill the caterpillar. Young larvae are much more susceptible to B.t. than are older larvae. As such, apply this pesticide in the spring as soon as bagworms are seen (usually in May) and repeat two weeks later. Control is most effective when spraying is done in late afternoon or early evening. This insecticide is very safe to use. Once the bags have reached ¾ inch long, the efficacy of B.t. sprays decreases rapidly.

Sprays applied later in the season (May and June), when bagworms are larger must be with a contact insecticide, such as permethrin, cyfluthrin, lambda cyhalothrin, carbaryl, malathion or acephate. Note that these insecticides will also reduce populations of beneficial insects (predators and parasitoids) that help control spruce spider mites, which can result in an outbreak of this occasional Leyland cypress pest. Soil application of neonicotinoid insecticides, such as imidacloprid or dinotefuran only give minimal (less than 10%) control from bagworm damage, and should not be substituted for spray control. See Table 1 for specific products. As with any pesticide, read and follow all label directions and precautions before using. Again, once a tree is tall, adequate coverage by a homeowner is often not feasible.”

If you call your local Master Gardener or extension office, they cannot recommend one service to get rid of the bag worms; but they might be allowed to give you a list of services that you can call to come to your house. Or go to the yellow pages and call around to find a reliable, certified arborist, landscaper or exterminating service in your area to see if they will come out to spray at this late date. Talk to them first and ask if it would be best to wait till next year in the early spring. Speak to a few different services to locate one that you feel comfortable with.  I suspect this bagworm problem is a major problem affecting many of the Leyland cypresses in your area.