It's hard to diagnose the issue without images of the symptoms, but often these native shrubs contract a very common fungal leaf spot. Older foliage (both those w/ spotting as well as those that are several years old) is naturally shed in spring as new growth prepares to emerge, which is normal. The leaf spot is so common that we rarely see wild Mountain-laurel without it, and while it can be an eyesore in a garden setting, it doesn't seem to cause the plant much harm in terms of overall health.

There is no fungicide that can cure existing symptoms, and while its use might suppress new infections on growth that is still healthy, we don't recommend its use since fungicides may harm other organisms, including pollinators. Aside from that concern, fungicides also don't always work to fully prevent new infections, and usually require several applications per year (as long as the plant lives) to maintain protection, which is not practical or cost-effective for most gardeners.

If the shrub has dying branches and browned, wilting leaves, that would indicate a different problem, likely tied to drought stress and a secondary infection that killed branches, or over-watering (or soil that stayed too wet at some point or which is too compacted to supply the roots with enough oxygen) that has weakened the root system. Mountain-laurel need moist but very well-drained soil that's acidic, and they struggle in soils that experience either moisture extreme (too dry or too wet).

Miri