The Worm Is Out of the Bag!
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Written by: Charlotte Glen, Horticulture Agent
Do you have shrubs that have been covered with brown, spindle shaped sacks all year? If so, your shrubs have bagworms and you need to treat now to prevent serious damage. Bagworms are a type of caterpillar that feed on many evergreen shrubs, especially conifers like Leyland cypress. They spend the winter as eggs inside their bags, but now they have hatched. They are out of the bag and are very hungry. Treating now will stop bagworms from feeding this year and will help prevent another outbreak next year. Both organic and synthetic insecticides are available to control this pest.
Bagworms are a type of caterpillar that builds a protective sack around their bodies out of leaves and needles from the plant they feed upon. Many gardeners initially mistake the bagworm’s sack for seed pods or cones. 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 of 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 have recently 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 two inches long, and they become more visible. Unfortunately by the time they become large enough to be readily noticeable, they are more difficult to control, especially with organic 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 start the cycle all over again next spring.
Treating for Bagworms
As with all caterpillar pests, gardeners have both organic and synthetic pesticide options for dealing with bagworms. All of these products are applied to plants as liquid sprays. Most can be bought as either concentrated products that are mixed in water, or as ready to use sprays that can be applied directly to plants. To find out how to mix and use the product you have, always read and follow label directions. Since bagworms tend to hatch all at one time, one treatment may be enough to control this pest. If some worms continue to feed after treating, spray again one to two weeks after the first application.
Organic Options – 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 an additional organic insecticide that will control bagworms as well as a wide range of insect pests. Organic 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, cyfluthrin, carbaryl (Sevin), or malathion. These are readily available at most garden centers. 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. If bees are actively working flowering plants in the area wait until late evening to spray, after bees have returned to the hive.
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.
If you have gardening questions, contact your local Cooperative Extension Office.
- If you live in Pender County, call 259-1235.
- In New Hanover County, call 798-7660
- In Brunswick County call 253-2610
- Or visit https://www.ces.ncsu.edu/