The bagworms appear to be too old for the use of B.t., one of the lowest-toxicity options, but there are a few other choices, some of which may need to be applied by a professional (certified pesticide applicator) for practical or legal reasons. Insect-killing nematodes (microscopic roundworms that parasitize the caterpillars) may work, but would require very thorough coverage that a professional sprayer can help with, given the height of the plants, and we're not sure how well they'll fare in this heat wave since they need to be applied wet and cannot dry out until they infect their host. A systemic pesticide, which is applied either to foliage (like spinosad) or roots (chlorantraniliprole or dinotefuran) and is absorbed, might work but some ingredients in this category are legally required to be applied by a professional, as they run the risk of harm to pollinators if they contaminate flowering plants.

The individual arborvitae that has lots of brown dieback will not recover and would need to be removed if that area of dead growth (which will eventually become bare) will be an eyesore.

Miri