Bagworm Damage

by Matthias Rich, ISA Certified Arborist


Bagworm Damage

The problem
Do you see little cocoons on your tree or shrub?  Evergreen bagworms hatch in mid-May and are most active by the end of July.  There can be hundreds of eggs in each bag!  The females are the ones that make the cocoon that is attached to the trees or shrubs in your landscape. They feed and use the needles and material around them with their silk to make strong bags, and the bag keep getting larger throughout the season. 

The problem is if you have active bagworms they can destroy a whole branch in an evergreen tree or shrub in a very short period of time. If left untreated they will destroy the entire plant in a season or less.  They will attack any evergreen tree, but they are most commonly found on evergreen trees such as, arborvitae, pine, and spruce trees.

Bagworm Damage
How to eradicate
There are sprays that can be used to eradicate bagworms, but it needs to be used when the females are feeding.  Most bagworms will be feeding in early May through August. The spray will not penetrate the bags so it is imperative that is done when they are actively feeding.  Typically, intervals of applications are necessary every 10 days for complete coverage or the pest control will be ineffective.  If you have a small population of bagworms, you can hand pick them off, or cut off the branches they are located on.  This method is less effective, but doesn’t require chemicals or specific timing. 

How to prevent it
Most people don’t notice a bagworm problem until late summer when the bagworms have grown to a larger size and their population is damaging their plant.  The best way to prevent large area damage is to check your evergreen plants frequently for any cocoons or areas with sparse growth.  If you can eliminate a couple of cocoons, it is a lot easier than taking care of hundreds of cocoons.


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