There is no treatment in terms of a spray or applied product, but old azaleas often need refreshing by way of drastic pruning. Sometimes branch dieback can be a result of conditions like Botryosphaeria canker, an opportunistic fungal disease that takes advantage of shrubs stressed by environmental conditions like drought. Drought alone can also cause dieback or poor foliage development, and azaleas grown in lots of direct sun can also become "twiggy" and decline in appearance over time. (We can't tell from the photos how much summer sun the shrub is getting, but they do best with some afternoon shade from either taller trees or a building shadow.)

Has the azalea been watered periodically during these past two years of drought? (Our Watering Trees and Shrubs page has guidance.) If not, it might be in decline due to the stress.

The growths on the branches are lichen, which is harmless and can be common on bark that gets lots of light. Its abundance may suggest that the plants are getting more light than they would generally prefer, since woodland-grown azaleas tend not to have much lichen on their branches.

Any dead or weak branches should be pruned off, and if you want to try renewal-pruning the azalea, you would either cut some of the main branches down close to the base of the plant, or cut all of them down to within around a foot of the ground. Regrowth may take a few years to fill back in again to where the plant looks refreshed and dense (and flowers normally), but it can help to rejuvenate an older shrub that is starting to decline or become unevenly shaped once dead wood is pruned out. The Brighton Dam Azalea Garden near the Howard-Montgomery County line does this with their multitudes of azalea shrubs; they take portions of a mass planting of an azalea variety and cut the shrubs down quite far to let them regrow.

If you were to prune out some (but not all) of the oldest stems, a process called "thinning," you could still enjoy flowers for the next year or so while the new growth begins to fill in, but the overall renewal process may take longer. In comparison, pruning all of the growth down at once will eliminate flowering for a year or more, but the regrowth will be more even in terms of symmetry. You don't have to do any renewal pruning, but just be aware that areas of bare growth (either due to shading from the shrub's upper branches or due to branch dieback over the years) will probably not fill back in on its own. That isn't a health issue for the shrub, just an aesthetic consideration.

Miri