Pest Alert: Bagworms Now Active in Landscapes

— Written By

The heat is on and the weeds seem to be about the only things doing well this summer. Even the insects seem too lazy to make much of an effort to annoy you these days. As sayings go, “messing and gomming” (see piddlin’) was applied liberally by my grandmother around this time of year, when it was too hot to do much in the garden besides wait for plants to produce and occasionally pull the errant weed. So as you find yourself putzing around the yard feeling sorry for your plants, keep your eyes open for those hungry menaces known as bagworms that, if left unchecked, can cause major problems later in the season.

What are bagworms?

A pest of many ornamental trees and shrubs, the bagworm is most easily identified by the cone-shaped bag that is spun at the ends of tree or shrub branches. The adult males are small, brown hairy moths that have clear wings while female adults spend their entire lives in the bags as grub-like worms. Adult females produce anywhere from 500 to 1000 eggs, which are laid inside the bag in the fall just before they die. The cocoon will protect the unhatched eggs throughout the winter until the larvae hatch in the spring months.

Sometime around April or May, newly hatched larvae will spin down on silken threads and get blown around by early spring winds until they land on a suitable host plant. At that point, larvae will begin feeding on the plants and spinning a “cone-like” casing that hangs down from the ends of branches. Even though bagworms have a wide range of plants upon which they feed, including many deciduous trees and shrubs, they are typically found on conifer plants, including juniper, arborvitae, cedar, and Leyland cypress.

It is not uncommon to see multiple bagworms on one tree as newly hatched larvae will typically stay on the same plant on which they hatched. Since the adult females lay many eggs in one year, it is not uncommon for a single tree to become defoliated in just two or three seasons. If you have planted evergreen trees as privacy screens and have multiple trees of the same species in one space, whole areas can become completely defoliated in a relatively short amount of time if the problem goes unchecked.

Monitoring and Controlling Bagworms

Because of their relatively small size and cryptic coloration, the young bagworms are difficult to spot. It is usually not until they have defoliated a plant or spun their cocoons that you may realize you have a problem. Begin monitoring plants now for signs of defoliation or chewing damage at the tips of branches. Also look for the large bags that begin to show up in late July and persist through September.

Generally, hand removal is adequate and can be done any time of the year. The easiest way to control bagworms is to pinch the bags or simply cut or pull cocoons from the branches or to pinch them. Once removed, bags should be destroyed.

There also are several species of wasps and flies that provide natural control as well. It has been demonstrated that when trees like arborvitae are surrounded by plants in the aster family, including coneflowers and black-eyed susans, parasitism rates of larvae are high. In fact, this type of biological control is adequate to keep bagworm infestations from getting out of hand and completely destroying landscape plants. Remember that when you diversify your landscape with flowering plants, you will attract a greater number of beneficial animals to help with pest management.

Despite the weather, it is not time to take a break from the garden just yet. Whether you are a messer and/or a gommer, a piddler, or a putzer, any one of these techniques applied in conservative amounts or in generous helpings will help protect and maximize plant health the rest of the season. I personally find that a little of each and a cold watermelon helps to relieves a lot of garden struggles this time of year.

Learn More!

 To learn more about bagworms and their control, or have other pest-related questions, visit http://ces.ncsu.edu, where you can post your questions via the ‘Ask an Expert’ link, or find your local Extension office.

Written By

Photo of Sam MarshallSam MarshallExtension Agent, Agriculture - Horticulture (910) 253-2610 (Office) wsmarsh2@ncsu.eduBrunswick County, North Carolina
Posted on Jul 13, 2015
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