Dying lower branches on large evergreens
Is it aphids, disease or old age that makes lower branches, except For tops, loose needles.
Montgomery County Maryland
You did not mention what type of tree you are referring to. In general insects and diseases are host specific. Factors that can cause decline include drought, soil compaction, planting too deeply, etc. When trees are subject to the above, they can be susceptible to insect and disease problems.
You can send us digital photos of the tree, around the base, and branches going from good to bad for more information.