Bagworms Usually Will Not Pose Major Problems-Until Ignored

By Jessica Strickland

Q: What causes the brown, diamond-shaped bags on my Leyland cypress?

 A: Often people describe bagworms as a diamond-shaped bag made up of a cluster of brown branches.  These bags are found attached to branches of many confers in the landscape.  There a couple of different insects that people refer to as bagworms.  The bagworms we are discussing here are not the ones that make webs in trees.

Bagworms are a common pest that occurs throughout North Carolina and have a wide host range but are usually found on conifer trees like arborvitae, junipers, cedars, and cypresses.  A few bagworms do little harm to a shrub or tree.  However, several bagworms on a shrub or tree can cause excessive defoliation.  Conifers do not fill in the defoliated areas with new growth and a severe infestation of bagworms could damage the plant over time.

Inside the bags is where the eggs overwinter.  The bags are made of silky material and the bagworms make the outside brown and incorporate plant material from the tree so that they are camouflaged.  The bags can be found attached to the twigs of trees during this time of year.

In May and June the eggs hatch and the larvae (worm) spin down on silken threads.  These small worms are blown by the wind to a new location.  Sometimes the worms can be seen dangling from the trees on a silk thread just waiting for a breeze to carry them to a new location.  Most of the larvae land on the original host plant but some small worms may be moved for some distance on the silk thread.  When the larvae lands at a new location they will begin forming a new bag.  As the bagworms grow, it enlarges the bag and adds fresh plant material to the outside.  The bag is firmly attached by a sturdy silk band which the bagworms usually wrap around a twig.

During this time of year, the best control practice is to hand-pick the bags off of plants before eggs hatch in late spring.  After picking off bags, they should be destroyed or removed from the area.  Often times people squash the bags or drop them in a bucket of soapy water to insure they are gone.  Chemical controls in the winter will not be effective because the bag provides protection to the insect inside.

Chemical controls are only effective in June and early July while the worms are small and relatively sensitive.  Several pesticides are available for homeowners including: Orthene (acephate), Sevin (carbaryl), and DiPel (Bt).  When using an insecticide, remember to carefully read and follow the label directions.

Bagworms usually are not a major pest problem but could become one if ignored and the population is allowed to increase over time.  The best defense is to carry a pair of pruners as you stroll through your landscape, and clip them off of branches as you see them.

For additional lawn and garden information contact the Wayne County Extension Master Gardener Volunteer Plant Clinic on Mondays and Wednesdays from 10am to 1pm. One can reach the Wayne County Extension Master Gardener Volunteer Plant Clinic by phone at 919-731-1433, e-mail at Master.Gardener@waynegov.com, or stopping by Room 100 of the Wayne County Extension Office (208 West Chestnut Street, Goldsboro).

Recommendations for the use of agricultural chemicals are included in this article as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this article does not imply endorsement by North Carolina Cooperative Extension nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical.

Source:ncsu.edu