Bagworm Damage:

Bagworms mainly feed on needled evergreens such as Leyland cypress, juniper, and arborvitaes. They are most active in the late summer. They can cause broad spread defoliation to host plants. 

Most all needled evergreens have older brown needles inside the green newer growth. Bagworms feed on the new, green needles, exposing the brown material inside the plant. They also cause a good amount of the newer green needles to turn brown. Most evergreens are very slow to repair the damage caused by bagworms. In many cases it takes multiple seasons for a plant damaged by bagworms to repair the damage caused.