News

Bag Worms

07.19.10

If you have noticed brown bags like these on your shrubs, you have bagworms. Treat now to prevent serious damage to evergreen shrubs! Both natural and synthetic pesticides are available to control these pests. 

Treat now - Bagworms are out!
Do you have shrubs that have been covered with brown, spindle shaped sacks all year? If so, you have bagworms and you need to treat now to prevent serious damage to your ornamental plants. Bagworms are a type of caterpillar that feed on many evergreen shrubs, especially conifers, including Leyland cypress. Treating now will stop bagworms from feeding this year and will help prevent another outbreak next year.

Bagworm Biology
Bagworms are a type of caterpillar that builds a protective sack around their bodies out of the plant they are feeding upon. Unfortunately these caterpillars eat a lot and tend to occur in large numbers, enabling them to quickly eat all the green leaves off their plant host. This is particularly bad for conifers, including cedars, Leyland cypress, arborvitae, and junipers, which are their favorite foods. Most conifers cannot recover from having all their foliage removed, whether by caterpillars or pruning shears, so heavy feeding by bagworms can kill these plants.

The bagworms that are currently feeding are very small. They hatched from eggs that were inside the bags created last year. If not treated, they will continue to feed and grow larger. As they grow their sacks get larger, up to around two inches long, and become more visible. Unfortunately by the time they become large enough to be readily noticeable, they are more difficult to control, especially with natural products. Later in the summer these caterpillars will stop feeding and will mature into their adult form, which is a moth. The moths will mate and lay eggs inside their bags, where the eggs will overwinter and hatch next spring.

Treating for Bagworms
Homeowners have both natural and synthetic pesticide options for dealing with bagworms. All of these products are applied to plants as liquid sprays. When bagworms are small they can be effectively treated with B.t. (Bacillus thuringiensis), a natural bacteria that kills only caterpillars and is sold under various brand names including DiPel, Green Light BT Worm Killer, and Safer Caterpillar Killer. Another natural, organic approved insecticide homeowners can use for bagworm control is spinosad, which is sold under brand names like Captain Jack’s Dead Bug Brew and Green Light Lawn & Garden Spray Spinosad Concentrate . Neem oil is additional natural insecticide that will control bagworms as well as a wide range of insect pests. These products are most effective when applied before bagworms reach ¾” in length.

Synthetic insecticides effective for bagworm control include those containing the active ingredient bifenthrin, permethrin, or cyfluthrin. To determine the active ingredient in any pesticide product check the label.  When treating make sure to get complete coverage of the infested plant and read and follow all label directions.

Once August arrives, treating bagworms is of no use because the caterpillars will have started to pupate and are completely unaffected by pesticides. If you notice bagworms on a plant after August, your only option is to pick them off by hand or wait to treat next year in early summer. Handpicking bagworms from plants in winter is an effective way to prevent future bagworm outbreaks, since the bags are full of overwintering eggs. Disclaimer: Recommendations for the use of 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 chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Read and follow all label directions when using any pesticide.

Learn More!
If you have questions about bagworms, or other pests in your landscape, contact your local Cooperative Extension office. In Pender County call 259-1235, visit our office at 801 S. Walker Street in Burgaw (office hours: Mon – Fri, 8am – 5pm), or post your questions online using our ‘Ask an Expert’ widget available at http://pender.ces.ncsu.edu.

Find out more about bagworms from this NC Extension fact sheet:http://www.ces.ncsu.edu/depts/ent/notes/O&T/trees/ort081e/ort081e.htm.

Charlotte D. Glen

Agriculture Agent - Horticulture 

NC Cooperative Extension, Pender County Center

801 S. Walker St.

Burgaw, N.C.  28425

Email : This email address is being protected from spambots. You need JavaScript enabled to view it.

Phone : (910) 259-1235

Fax: (910) 259-1291

http://pender.ces.ncsu.edu

http://pendergardener.blogspot.com/