If is the older, inside needles of your evergreen trees and shrubs that are browning and dropping it is neither a disease nor and insect; it is normal fall needle drop.
It can be a startling sight, but many narrow-leaved evergreens shed their oldest needles each year, before winter. The inner most needles will yellow while the new, outer needles stay bright green. The yellow needles eventually drop and carpet the ground around the tree. It may look alarming, but it is normal and healthy.
Evergreen needles do not live forever. You may not notice the regular shedding of needles, because new needles are produced every year. Older needles may turn yellow, red or brown and go unnoticed before dropping. Different types of evergreens drop their needles at different rates. For instance, most pines will shed every 2--5 years, while spruce trees hang on to them for 5--7.
Yellow needles early in the season and yellowing of newer growth are different stories. If that should happen, look for other causes, such as drought, insects, like spider mites or other symptoms on the needles, bark and roots that could be causing desiccation.