bag worms - Ask Extension
My sister has bag worms all over the evergreen plants in her front yard. She has tried picking them off but they are so numerous that she is consider...
Knowledgebase
bag worms #797268
Asked June 22, 2022, 2:01 PM EDT
My sister has bag worms all over the evergreen plants in her front yard. She has tried picking them off but they are so numerous that she is considering spraying. Is there something else she can do? If she decides to use a spray, is there a least dangerous one you recommend?
Montgomery County Maryland
Expert Response
Hand removal is definitely the least impactful approach, but we realize this is tedious or impossible when caterpillars are too high to reach or too well-camouflaged. Two lower-risk pesticides are options: first, while caterpillars are still fairly young (as they are now), she can try a product with the active ingredient of Bt. (This stands for Bacillus thuringiensis, a naturally-occurring bacterium which is toxic to certain insects. Specific strains are used for targeting caterpillars, reducing the risk of negative impacts even further.)
Later, if older caterpillars (larger bags) are discovered that escaped earlier efforts at removal, Bt will be less effective, but the active ingredient spinosad will still suppress them. Spinosad is a bit less targeted in that other leaf-feeding insects (and potentially exposed bees, though in this case there's no flower draw) could be impacted, but it's still better than more broad-spectrum insecticide ingredients like pyrethroids.
Follow the directions on any product selected (several brands and formulations use either of these ingredients), and verify it is labeled for use on the types of plants and locations she needs to use it for. In this case, the label wording may say something like "evergreen shrubs," "trees," "landscapes," "gardens," etc. (This is more applicable to any pesticides purchased online, and is less of an issue with those stocked at local garden centers, but a pesticide label should always be read in its entirety regardless before purchase and use.)
Thorough coverage of all the foliage is essential for good efficacy, since the caterpillars need to ingest treated foliage to be affected. If the plants are too tall to spray herself, she should hire a professional pesticide applicator (usually employed by landscaping or tree-care companies), who will not only have the right equipment to coat the foliage with spray, but will also have personal protective equipment to safeguard against dripping spray or drifting mist from overhead application. The person can provide her with a copy of the pesticide label for reference. Several re-treatments may be needed, but this information will be included on the label and could vary depending on the exact formulation.
Feeding ceases relatively soon after the insects ingest treated foliage. Dead caterpillars might not necessarily fall off the plants right away though, especially since bags are tied with silk to branches when the caterpillars aren't actively toting them about. Therefore, a good indicator that a treatment is working is simply that no new damage is seen over time; eventually, the bags will disintegrate or fall off.
A few more details about this pest can be found on our Bagworms on Trees and Shrubs page.
Miri
Later, if older caterpillars (larger bags) are discovered that escaped earlier efforts at removal, Bt will be less effective, but the active ingredient spinosad will still suppress them. Spinosad is a bit less targeted in that other leaf-feeding insects (and potentially exposed bees, though in this case there's no flower draw) could be impacted, but it's still better than more broad-spectrum insecticide ingredients like pyrethroids.
Follow the directions on any product selected (several brands and formulations use either of these ingredients), and verify it is labeled for use on the types of plants and locations she needs to use it for. In this case, the label wording may say something like "evergreen shrubs," "trees," "landscapes," "gardens," etc. (This is more applicable to any pesticides purchased online, and is less of an issue with those stocked at local garden centers, but a pesticide label should always be read in its entirety regardless before purchase and use.)
Thorough coverage of all the foliage is essential for good efficacy, since the caterpillars need to ingest treated foliage to be affected. If the plants are too tall to spray herself, she should hire a professional pesticide applicator (usually employed by landscaping or tree-care companies), who will not only have the right equipment to coat the foliage with spray, but will also have personal protective equipment to safeguard against dripping spray or drifting mist from overhead application. The person can provide her with a copy of the pesticide label for reference. Several re-treatments may be needed, but this information will be included on the label and could vary depending on the exact formulation.
Feeding ceases relatively soon after the insects ingest treated foliage. Dead caterpillars might not necessarily fall off the plants right away though, especially since bags are tied with silk to branches when the caterpillars aren't actively toting them about. Therefore, a good indicator that a treatment is working is simply that no new damage is seen over time; eventually, the bags will disintegrate or fall off.
A few more details about this pest can be found on our Bagworms on Trees and Shrubs page.
Miri
Thank you so much. This is super helpful. I have shared with my sister and we are both equipped for any future problems.
Very grateful for this service!
Kate
You're welcome!
