Bag Worms

Description:
Bag worms spin their homes out of silk and bark and leaves. The final casing resembles a pine cone and is often mistaken for such because they primarily feed on cone bearing plants. The caterpillar (Thyridopteryx ephemeraeformis) hides inside the bag and pokes its head out the top to eat.

Damage:
It is amazing the damage these little guys can do! They can defoliate entire plants in no time, often killing evergreens. Bag worms are most often found on evergreen, needle-leaved plants like juniper, spruce, and arborvitae. They will occasionally attack deciduous trees such as honey locust and bald cypress. Deciduous plants are more likely to recover from defoliation than evergreens.

Prevention:
The best way to prevent infestation is to hand pick and destroy all bags as soon as they appear.

Management:
Mild Infestations: The most effective way to control bag worms is to physically remove and destroy the bags. This can be done as long as there are not many bags present. Young bag worms (in bags less than 1/2") are susceptible to applications of BT (Bacillus thuringiensis kurstaki). Always follow label directions.

Sever Infestations: One bag can overwinter 500 to 1000 eggs! So do not allow bags to overwinter. In May or June the many, many larvae emerge from the bags and spiral down silk strands. This is a very good time to spray with BT. If the larvae make it to adults a stronger pesticide will be required, such as malathion, diazinon, carbaryl (Sevin), or acephate (Orthene.) Always follow label directions.