Conifers and evergreens are susceptible to a variety of causal factors that can cause lower branches to turn brown and die. Sometimes the cause is as simple as that they are being shaded by the upper growth and die for lack of sunlight. Other times the culprits are disease, insect or other climatic factors.
Cankers, lesions on the branches that restrict the movement of water and nutrients to the branch and foliage, are the most common reason lower branches die on conifers, especially spruces. Cytospora kunzei is the fungus responsible. The disease presents on the lowest branches first and then moves up the tree. This disease is most effectively controlled when first noticed. Remove all dead and dying branches in winter when the disease is dormant and use sterile cutting tools to further prevent its spread.
Galls are brown to purple growths on the ends of conifer branches that people sometimes mistake for cones. Their origin is actually a type of wasp. As the galls continue to develop, they suck more nutrients from the branches and in severe cases can kill them. Chemical control is not needed as the galls can just be pruned off. Like canker diseases, galls are more effective to treat when first noticed.
Needle problems of conifers can start anywhere on the tree. Sometimes they start on the north side such as in cases of brown spot. Other times they start at the top, and sometimes the bottom. Needle casts occur on the current year's growth once mature and causes needles to turn brown. Good cultural practices, such as making sure your conifers receive enough sunlight, have good drainage and receive appropriate fertiliser while they are getting established, can help to prevent many of these needle diseases.
Insect vectors and disease pathogens are not always the reason lower branches on conifers turn brown. Winter injury is often the cause if damage is present in late winter to early spring. Winter's drying winds cause whatever moisture is still stored in the needles to evaporate. The dormant roots in the frozen soil cannot replace the lost water. The resulting damage can cause browning of affected branches. If inner needles only are dying and falling in autumn months, this is a common part of a conifer's annual cycle and should cause no concern.