Insects on blue spruce

Asked July 8, 2020, 9:30 AM EDT

What are these insects on a blue spruce and is there anything we can do to eradicate them?

Frederick County Maryland

3 Responses

These are young bagworms. If you can reach them all remove them and throw them into a bucket of soapy water to kill them. They can be a serious pest of evergreens. If you need to spray use Bacillus thuringiensis, often called Bt, it is a type of bacteria that only kills certain insects and does not affect humans or animals. Or you can use spinosad.
Please refer to the following information from our website,
https://extension.umd.edu/hgic/topics/bagworms-trees-and-shrubs

Deb

We have sprayed with Bt for the last couple of weeks but are noticing many large bags now. We have been picking them off daily but seem to find new ones each time we look. The tree has dense needles and we feel that we are surely missing the infestation. Since Bt only works on the the young bagworms, do we need to continue the spray regimen? I noticed that the Extension publication indicated chemical control might be warranted. Is there something else we can do?

You can switch to spinosad now if the B.t. is no longer working and the caterpillars are getting too large for it to be effective. After the bagworms ingest the spray residue they should cease feeding in a few hours, though death may take a few days. As with B.t., the spray should thoroughly coat the foliage and it too will likely need re-application; check the bottle label for the details as each product is different.

Miri