Bagworms...what to do
We have a large stand of arborvitae in Fallston Harford county. We planted them as a visual barrier between our property and the (messy) neighbor next door. Now these trees are covered in bag worms, and one had to be cut down as it was dead. We really don’t want to spray them since there are all kinds of toads, frogs, butterflies and bees around. Our property is 3 1/2 acres and includes a small creek at the back end of it. There are obviously too many bags of worms to pick off by hand plus these trees are too tall to get the ones up high and there are a lot of trees! Our question: is there something to spray that won’t kill the aforementioned critters What happens if we do nothing...should we just take our chances on nature taking care of the pests?
It is too late in the season now to use any type of pesticide that would be effective for controlling bagworms. You could hire someone to manually remove the bags that are high up in the trees -- this will remove the overwintering insects so they can't start a new generation the next year. The next option would be to monitor the trees for young bagworms (usually around early June) and treat the caterpillars with the biological product called Bacillus thuringiensis (Bt). It is a type of bacteria that only kills certain insects and does not affect humans or animals.
Here is our page on bagworms with all the specifics: https://extension.umd.edu/hgic/topics/bagworms-trees-and-shrubs
If you have a lot of all of the same type of tree, then you have a great food source for the bagworms. When planting screening trees, it is a good idea to diversify your plant choices. Using several species instead of many of one type provides resilience against pest and disease outbreaks. If there is a pest/disease problem, you will not lose the whole stand if you have a mixed planting. It is something to think about for the future if you decide to replace the Arborvitaes that have bagworm problems.